Android知识总结
一、测量
ViewRootImpl.java
private void performTraversals() {
//这里的mView在setView中被赋值为DecorView
final View host = mView;
//mAdded指DecorView是否被成功加入到window中，在setView()中被赋值为true
if (host == null || !mAdded)
return;
mIsInTraversal = true;
mWillDrawSoon = true;
boolean windowSizeMayChange = false;
WindowManager.LayoutParams lp = mWindowAttributes;
//期望的宽高
int desiredWindowWidth;
int desiredWindowHeight;
final int viewVisibility = getHostVisibility();
final boolean viewVisibilityChanged = !mFirst
&& (mViewVisibility != viewVisibility || mNewSurfaceNeeded
// Also check for possible double visibility update, which will make current
// viewVisibility value equal to mViewVisibility and we may miss it.
|| mAppVisibilityChanged);
mAppVisibilityChanged = false;
final boolean viewUserVisibilityChanged = !mFirst &&
((mViewVisibility == View.VISIBLE) != (viewVisibility == View.VISIBLE));
WindowManager.LayoutParams params = null;
CompatibilityInfo compatibilityInfo =
mDisplay.getDisplayAdjustments().getCompatibilityInfo();
if (compatibilityInfo.supportsScreen() == mLastInCompatMode) {
params = lp;
mFullRedrawNeeded = true;
mLayoutRequested = true;
if (mLastInCompatMode) {
params.privateFlags &= ~WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
mLastInCompatMode = false;
} else {
params.privateFlags |= WindowManager.LayoutParams.PRIVATE_FLAG_COMPATIBLE_WINDOW;
mLastInCompatMode = true;
}
}
//用来保存窗口宽度和高度，来自于全局变量mWinFrame，这个mWinFrame保存了窗口最新尺寸
Rect frame = mWinFrame;
//mFirst在构造器中被初始化为true，表示第一次performTraversals()
if (mFirst) {
//设置需要全部重新draw
mFullRedrawNeeded = true;
//需要重新layout
mLayoutRequested = true;
final Configuration config = mContext.getResources().getConfiguration();
// 判断要绘制的窗口是否包含状态栏，然后确定要绘制的Decorview的高度和宽度
// 有的话就去掉
if (shouldUseDisplaySize(lp)) {
// NOTE -- system code, won't try to do compat mode.
Point size = new Point();
mDisplay.getRealSize(size);
desiredWindowWidth = size.x;
desiredWindowHeight = size.y;
} else if (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT
|| lp.height == ViewGroup.LayoutParams.WRAP_CONTENT) {
//宽度和高度为整个屏幕的值，当此时才最大进行3次测量
desiredWindowWidth = dipToPx(config.screenWidthDp);
desiredWindowHeight = dipToPx(config.screenHeightDp);
} else {
desiredWindowWidth = frame.width();
desiredWindowHeight = frame.height();
}
mAttachInfo.mUse32BitDrawingCache = true;
mAttachInfo.mWindowVisibility = viewVisibility;
mAttachInfo.mRecomputeGlobalAttributes = false;
mLastConfigurationFromResources.setTo(config);
mLastSystemUiVisibility = mAttachInfo.mSystemUiVisibility;
// Set the layout direction if it has not been set before (inherit is the default)
if (mViewLayoutDirectionInitial == View.LAYOUT_DIRECTION_INHERIT) {
host.setLayoutDirection(config.getLayoutDirection());
}
host.dispatchAttachedToWindow(mAttachInfo, 0);
mAttachInfo.mTreeObserver.dispatchOnWindowAttachedChange(true);
dispatchApplyInsets(host);
} else {
//如果不是第一次performTraversals()
//它的当前宽度和高度就从之前的保存在ViewRootImpl类的成员变量mWinFrame/frame获取
desiredWindowWidth = frame.width();
desiredWindowHeight = frame.height();
// mWidth和mHeight是由WindowManagerService服务计算出的窗口大小，
// 如果这次测量的窗口大小与这两个值不同，说明WMS单方面改变了窗口的尺寸
if (desiredWindowWidth != mWidth || desiredWindowHeight != mHeight) {
if (DEBUG_ORIENTATION) Log.v(mTag, "View " + host + " resized to: " + frame);
// 需要进行全部重绘以适应新的窗口尺寸
mFullRedrawNeeded = true;
//需要重新布局
mLayoutRequested = true;
// window窗口大小改变
windowSizeMayChange = true;
}
}
if (viewVisibilityChanged) {
mAttachInfo.mWindowVisibility = viewVisibility;
host.dispatchWindowVisibilityChanged(viewVisibility);
if (viewUserVisibilityChanged) {
host.dispatchVisibilityAggregated(viewVisibility == View.VISIBLE);
}
if (viewVisibility != View.VISIBLE || mNewSurfaceNeeded) {
endDragResizing();
destroyHardwareResources();
}
}
// Non-visible windows can't hold accessibility focus.
if (mAttachInfo.mWindowVisibility != View.VISIBLE) {
host.clearAccessibilityFocus();
}
// Execute enqueued actions on every traversal in case a detached view enqueued an action
getRunQueue().executeActions(mAttachInfo.mHandler);
boolean cutoutChanged = false;
boolean layoutRequested = mLayoutRequested && (!mStopped || mReportNextDraw);
// 要求重新测量
// 进行预测量
if (layoutRequested) {
final Resources res = mView.getContext().getResources();
// 如果是第一次
if (mFirst) {
// make sure touch mode code executes by setting cached value
// to opposite of the added touch mode.
//视图窗口当前是否处于触摸模式
mAttachInfo.mInTouchMode = !mAddedTouchMode;
//确保window的触摸模式已经打开
//内部 mAttachInfo.mInTouchMode = inTouchMode
ensureTouchModeLocally(mAddedTouchMode);
} else {
if (!mPendingDisplayCutout.equals(mAttachInfo.mDisplayCutout)) {
cutoutChanged = true;
}
//如果将窗口的宽或高设置为wrap_content了，最终还是会变为屏幕大小
if (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT
|| lp.height == ViewGroup.LayoutParams.WRAP_CONTENT) {
//窗口大小可能改变
windowSizeMayChange = true;
if (shouldUseDisplaySize(lp)) {
// NOTE -- system code, won't try to do compat mode.
Point size = new Point();
mDisplay.getRealSize(size);
desiredWindowWidth = size.x;
desiredWindowHeight = size.y;
} else {
Configuration config = res.getConfiguration();
desiredWindowWidth = dipToPx(config.screenWidthDp);
desiredWindowHeight = dipToPx(config.screenHeightDp);
}
}
}
// 进行预测量窗口大小，以达到更好的显示大小
// 比如dialog可能就是显示几个字而被铺满屏幕是奇怪的，通过measureHierarchy()去优化，
//尝试更小的宽度是否合适，这个方法会调用performMeasure()确定window大小，返回窗口大小是否会改变
// host: Decor lp: window attr rs: decor res
// desiredWindowWidth/Height: 上面初始的窗口期望宽高
windowSizeMayChange |= measureHierarchy(host, lp, res,
desiredWindowWidth, desiredWindowHeight);
}
if (collectViewAttributes()) {
params = lp;
}
if (mAttachInfo.mForceReportNewAttributes) {
mAttachInfo.mForceReportNewAttributes = false;
params = lp;
}
if (mFirst || mAttachInfo.mViewVisibilityChanged) {
mAttachInfo.mViewVisibilityChanged = false;
int resizeMode = mSoftInputMode & SOFT_INPUT_MASK_ADJUST;
// If we are in auto resize mode, then we need to determine
// what mode to use now.
if (resizeMode == WindowManager.LayoutParams.SOFT_INPUT_ADJUST_UNSPECIFIED) {
final int N = mAttachInfo.mScrollContainers.size();
for (int i=0; i由上面预测量中测量（performMeasure）次数最大为 3 次。
二、View 解析
2.1、measure
首先 ViewRootImpl 的 performMeasure 方法进入View 的测量
private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
if (mView == null) {
return;
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
try {
//执行 View 的 measure
mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
调用 View 的 measure 方法
public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
boolean optical = isLayoutModeOptical(this);
if (optical != isLayoutModeOptical(mParent)) {
//重新测量
Insets insets = getOpticalInsets();
int oWidth = insets.left + insets.right;
int oHeight = insets.top + insets.bottom;
widthMeasureSpec = MeasureSpec.adjust(widthMeasureSpec, optical ? -oWidth : oWidth);
heightMeasureSpec = MeasureSpec.adjust(heightMeasureSpec, optical ? -oHeight : oHeight);
}
// Suppress sign extension for the low bytes
long key = (long) widthMeasureSpec << 32 | (long) heightMeasureSpec & 0xffffffffL;
if (mMeasureCache == null) mMeasureCache = new LongSparseLongArray(2);
final boolean forceLayout = (mPrivateFlags & PFLAG_FORCE_LAYOUT) == PFLAG_FORCE_LAYOUT;
final boolean specChanged = widthMeasureSpec != mOldWidthMeasureSpec
|| heightMeasureSpec != mOldHeightMeasureSpec;
final boolean isSpecExactly = MeasureSpec.getMode(widthMeasureSpec) == MeasureSpec.EXACTLY
&& MeasureSpec.getMode(heightMeasureSpec) == MeasureSpec.EXACTLY;
final boolean matchesSpecSize = getMeasuredWidth() == MeasureSpec.getSize(widthMeasureSpec)
&& getMeasuredHeight() == MeasureSpec.getSize(heightMeasureSpec);
final boolean needsLayout = specChanged
&& (sAlwaysRemeasureExactly || !isSpecExactly || !matchesSpecSize);
if (forceLayout || needsLayout) {
// first clears the measured dimension flag
mPrivateFlags &= ~PFLAG_MEASURED_DIMENSION_SET;
resolveRtlPropertiesIfNeeded();
int cacheIndex = forceLayout ? -1 : mMeasureCache.indexOfKey(key);
if (cacheIndex < 0 || sIgnoreMeasureCache) {
//没有缓存，进行测量
//这里就是我们绘制 View 用的 onMeasure 方法了
onMeasure(widthMeasureSpec, heightMeasureSpec);
mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
} else {
long value = mMeasureCache.valueAt(cacheIndex);
// Casting a long to int drops the high 32 bits, no mask needed
// 有缓存，利用缓存的值
setMeasuredDimensionRaw((int) (value >> 32), (int) value);
mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
}
// flag not set, setMeasuredDimension() was not invoked, we raise
// an exception to warn the developer
//setMeasuredDimension 没有调用抛出异常
if ((mPrivateFlags & PFLAG_MEASURED_DIMENSION_SET) != PFLAG_MEASURED_DIMENSION_SET) {
throw new IllegalStateException("View with id " + getId() + ": "
+ getClass().getName() + "#onMeasure() did not set the"
+ " measured dimension by calling"
+ " setMeasuredDimension()");
}
//重置标志位
mPrivateFlags |= PFLAG_LAYOUT_REQUIRED;
}
mOldWidthMeasureSpec = widthMeasureSpec;
mOldHeightMeasureSpec = heightMeasureSpec;
mMeasureCache.put(key, ((long) mMeasuredWidth) << 32 |
(long) mMeasuredHeight & 0xffffffffL); // suppress sign extension
}
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
boolean optical = isLayoutModeOptical(this);
if (optical != isLayoutModeOptical(mParent)) {
//计算测量
Insets insets = getOpticalInsets();
int opticalWidth = insets.left + insets.right;
int opticalHeight = insets.top + insets.bottom;
measuredWidth += optical ? opticalWidth : -opticalWidth;
measuredHeight += optical ? opticalHeight : -opticalHeight;
}
setMeasuredDimensionRaw(measuredWidth, measuredHeight);
}
最终都会调用 setMeasuredDimensionRaw方法，更改 mPrivateFlags标志
private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
mMeasuredWidth = measuredWidth;
mMeasuredHeight = measuredHeight;
//标志位标志已经测量了 ， mPrivateFlags = true
mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
}
- 最后我们看下
MeasureSpec。
public static class MeasureSpec {
//低30位，存放的值
private static final int MODE_SHIFT = 30;
//高2位，存放的模式
private static final int MODE_MASK = 0x3 << MODE_SHIFT;
@IntDef({UNSPECIFIED, EXACTLY, AT_MOST})
@Retention(RetentionPolicy.SOURCE)
public @interface MeasureSpecMode {}
/**
* UNSPECIFIED 模式：
* 父View不对子View有任何限制，子View需要多大就多大
*/
public static final int UNSPECIFIED = 0 << MODE_SHIFT;
/**
* EXACTYLY 模式：
* 父View已经测量出子Viwe所需要的精确大小，这时候View的最终大小
* 就是SpecSize所指定的值。对应于match_parent和精确数值这两种模式
*/
public static final int EXACTLY = 1 << MODE_SHIFT;
/**
* AT_MOST 模式：
* 子View的最终大小是父View指定的SpecSize值，并且子View的大小不能大于这个值，
* 即对应wrap_content这种模式
*/
public static final int AT_MOST = 2 << MODE_SHIFT;
//将size和mode打包成一个32位的int型数值
//高2位表示SpecMode，测量模式，低30位表示SpecSize，某种测量模式下的规格大小
public static int makeMeasureSpec(int size, int mode) {
if (sUseBrokenMakeMeasureSpec) {
return size + mode;
} else {
return (size & ~MODE_MASK) | (mode & MODE_MASK);
}
}
//将32位的MeasureSpec解包，返回SpecMode,测量模式
public static int getMode(int measureSpec) {
return (measureSpec & MODE_MASK);
}
//将32位的MeasureSpec解包，返回SpecSize，某种测量模式下的规格大小
public static int getSize(int measureSpec) {
return (measureSpec & ~MODE_MASK);
}
...
}
2.2、layout
首先 ViewRootImpl 的 performLayout 方法进入View 的布局
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
int desiredWindowHeight) {
mScrollMayChange = true;
mInLayout = true;
final View host = mView;
if (host == null) {
return;
}
if (DEBUG_ORIENTATION || DEBUG_LAYOUT) {
Log.v(mTag, "Laying out " + host + " to (" +
host.getMeasuredWidth() + ", " + host.getMeasuredHeight() + ")");
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout");
try {
//调用View的Layout方法进行布局
host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
mInLayout = false;
//在ViewRootImpl进行布局的期间，Window内的View自己进行requestLayout
int numViewsRequestingLayout = mLayoutRequesters.size();
if (numViewsRequestingLayout > 0) {
ArrayList validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters,
false);
if (validLayoutRequesters != null) {
mHandlingLayoutInLayoutRequest = true;
// Process fresh layout requests, then measure and layout
int numValidRequests = validLayoutRequesters.size();
for (int i = 0; i < numValidRequests; ++i) {
final View view = validLayoutRequesters.get(i);
Log.w("View", "requestLayout() improperly called by " + view +
" during layout: running second layout pass");
//请求对该View布局，最终回调到ViewRootImpl的requestLayout进行重新测量、布局、绘制
view.requestLayout();
}
measureHierarchy(host, lp, mView.getContext().getResources(),
desiredWindowWidth, desiredWindowHeight);
mInLayout = true;
host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
mHandlingLayoutInLayoutRequest = false;
validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, true);
if (validLayoutRequesters != null) {
final ArrayList finalRequesters = validLayoutRequesters;
// Post second-pass requests to the next frame
getRunQueue().post(new Runnable() {
@Override
public void run() {
int numValidRequests = finalRequesters.size();
for (int i = 0; i < numValidRequests; ++i) {
final View view = finalRequesters.get(i);
Log.w("View", "requestLayout() improperly called by " + view +
" during second layout pass: posting in next frame");
//请求对该View布局，最终回调到ViewRootImpl的requestLayout进行重新测量、布局、绘制
view.requestLayout();
}
}
});
}
}
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
mInLayout = false;
}
接下来看 View 的 layout 方法
public void layout(int l, int t, int r, int b) {
if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
}
int oldL = mLeft;
int oldT = mTop;
int oldB = mBottom;
int oldR = mRight;
boolean changed = isLayoutModeOptical(mParent) ?
setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);
if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
//布局发生变化，调用 onLayout 方法设置布局
onLayout(changed, l, t, r, b);
if (shouldDrawRoundScrollbar()) {
if(mRoundScrollbarRenderer == null) {
mRoundScrollbarRenderer = new RoundScrollbarRenderer(this);
}
} else {
mRoundScrollbarRenderer = null;
}
mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnLayoutChangeListeners != null) {
ArrayList listenersCopy =
(ArrayList)li.mOnLayoutChangeListeners.clone();
int numListeners = listenersCopy.size();
for (int i = 0; i < numListeners; ++i) {
listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
}
}
}
final boolean wasLayoutValid = isLayoutValid();
mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
if (!wasLayoutValid && isFocused()) {
mPrivateFlags &= ~PFLAG_WANTS_FOCUS;
if (canTakeFocus()) {
// We have a robust focus, so parents should no longer be wanting focus.
clearParentsWantFocus();
} else if (getViewRootImpl() == null || !getViewRootImpl().isInLayout()) {
clearFocusInternal(null, /* propagate */ true, /* refocus */ false);
clearParentsWantFocus();
} else if (!hasParentWantsFocus()) {
// original requestFocus was likely on this view directly, so just clear focus
clearFocusInternal(null, /* propagate */ true, /* refocus */ false);
}
// otherwise, we let parents handle re-assigning focus during their layout passes.
} else if ((mPrivateFlags & PFLAG_WANTS_FOCUS) != 0) {
mPrivateFlags &= ~PFLAG_WANTS_FOCUS;
View focused = findFocus();
if (focused != null) {
// Try to restore focus as close as possible to our starting focus.
if (!restoreDefaultFocus() && !hasParentWantsFocus()) {
// Give up and clear focus once we've reached the top-most parent which wants
// focus.
focused.clearFocusInternal(null, /* propagate */ true, /* refocus */ false);
}
}
}
if ((mPrivateFlags3 & PFLAG3_NOTIFY_AUTOFILL_ENTER_ON_LAYOUT) != 0) {
mPrivateFlags3 &= ~PFLAG3_NOTIFY_AUTOFILL_ENTER_ON_LAYOUT;
notifyEnterOrExitForAutoFillIfNeeded(true);
}
notifyAppearedOrDisappearedForContentCaptureIfNeeded(true);
}
我们自定义 View 可以重写下面方法
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
}
2.3、draw
首先 ViewRootImpl 的 performDraw 方法进入View 的绘制
private void performDraw() {
if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) {
return;
} else if (mView == null) {
return;
}
final boolean fullRedrawNeeded = mFullRedrawNeeded || mReportNextDraw;
mFullRedrawNeeded = false;
mIsDrawing = true;
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw");
boolean usingAsyncReport = false;
boolean reportNextDraw = mReportNextDraw; // Capture the original value
if (mAttachInfo.mThreadedRenderer != null && mAttachInfo.mThreadedRenderer.isEnabled()) {
ArrayList commitCallbacks = mAttachInfo.mTreeObserver
.captureFrameCommitCallbacks();
final boolean needFrameCompleteCallback = mNextDrawUseBLASTSyncTransaction ||
(commitCallbacks != null && commitCallbacks.size() > 0) ||
mReportNextDraw;
usingAsyncReport = mReportNextDraw;
if (needFrameCompleteCallback) {
final Handler handler = mAttachInfo.mHandler;
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback((long frameNr) -> {
finishBLASTSync(!mSendNextFrameToWm);
handler.postAtFrontOfQueue(() -> {
if (reportNextDraw) {
// TODO: Use the frame number
pendingDrawFinished();
}
if (commitCallbacks != null) {
for (int i = 0; i < commitCallbacks.size(); i++) {
commitCallbacks.get(i).run();
}
}
});});
}
}
try {
if (mNextDrawUseBLASTSyncTransaction) {
if (mAttachInfo.mThreadedRenderer != null) {
mAttachInfo.mThreadedRenderer.pause();
}
mNextReportConsumeBLAST = true;
mNextDrawUseBLASTSyncTransaction = false;
if (mBlastBufferQueue != null) {
mBlastBufferQueue.setNextTransaction(mRtBLASTSyncTransaction);
}
}
boolean canUseAsync = draw(fullRedrawNeeded);
if (usingAsyncReport && !canUseAsync) {
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback(null);
usingAsyncReport = false;
finishBLASTSync(true /* apply */);
}
} finally {
mIsDrawing = false;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
// For whatever reason we didn't create a HardwareRenderer, end any
// hardware animations that are now dangling
if (mAttachInfo.mPendingAnimatingRenderNodes != null) {
final int count = mAttachInfo.mPendingAnimatingRenderNodes.size();
for (int i = 0; i < count; i++) {
mAttachInfo.mPendingAnimatingRenderNodes.get(i).endAllAnimators();
}
mAttachInfo.mPendingAnimatingRenderNodes.clear();
}
if (mReportNextDraw) {
mReportNextDraw = false;
// if we're using multi-thread renderer, wait for the window frame draws
if (mWindowDrawCountDown != null) {
try {
mWindowDrawCountDown.await();
} catch (InterruptedException e) {
Log.e(mTag, "Window redraw count down interrupted!");
}
mWindowDrawCountDown = null;
}
if (mAttachInfo.mThreadedRenderer != null) {
mAttachInfo.mThreadedRenderer.setStopped(mStopped);
}
if (LOCAL_LOGV) {
Log.v(mTag, "FINISHED DRAWING: " + mWindowAttributes.getTitle());
}
if (mSurfaceHolder != null && mSurface.isValid()) {
SurfaceCallbackHelper sch = new SurfaceCallbackHelper(this::postDrawFinished);
SurfaceHolder.Callback callbacks[] = mSurfaceHolder.getCallbacks();
sch.dispatchSurfaceRedrawNeededAsync(mSurfaceHolder, callbacks);
} else if (!usingAsyncReport) {
if (mAttachInfo.mThreadedRenderer != null) {
mAttachInfo.mThreadedRenderer.fence();
}
pendingDrawFinished();
}
}
if (mPerformContentCapture) {
performContentCaptureInitialReport();
}
}
private boolean draw(boolean fullRedrawNeeded) {
Surface surface = mSurface;
if (!surface.isValid()) {
return false;
}
if (DEBUG_FPS) {
trackFPS();
}
if (!sFirstDrawComplete) {
synchronized (sFirstDrawHandlers) {
sFirstDrawComplete = true;
final int count = sFirstDrawHandlers.size();
for (int i = 0; i< count; i++) {
mHandler.post(sFirstDrawHandlers.get(i));
}
}
}
//输入 和 弹出输入框
scrollToRectOrFocus(null, false);
if (mAttachInfo.mViewScrollChanged) {
mAttachInfo.mViewScrollChanged = false;
mAttachInfo.mTreeObserver.dispatchOnScrollChanged();
}
boolean animating = mScroller != null && mScroller.computeScrollOffset();
final int curScrollY;
if (animating) {
curScrollY = mScroller.getCurrY();
} else {
curScrollY = mScrollY;
}
if (mCurScrollY != curScrollY) {
mCurScrollY = curScrollY;
fullRedrawNeeded = true;
if (mView instanceof RootViewSurfaceTaker) {
((RootViewSurfaceTaker) mView).onRootViewScrollYChanged(mCurScrollY);
}
}
final float appScale = mAttachInfo.mApplicationScale;
final boolean scalingRequired = mAttachInfo.mScalingRequired;
//生成绘制区域
final Rect dirty = mDirty;
if (mSurfaceHolder != null) {
// The app owns the surface, we won't draw.
dirty.setEmpty();
if (animating && mScroller != null) {
mScroller.abortAnimation();
}
return false;
}
//如果需要全屏绘制，则将dirty区域宽高设为全屏
if (fullRedrawNeeded) {
dirty.set(0, 0, (int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f));
}
if (DEBUG_ORIENTATION || DEBUG_DRAW) {
Log.v(mTag, "Draw " + mView + "/"
+ mWindowAttributes.getTitle()
+ ": dirty={" + dirty.left + "," + dirty.top
+ "," + dirty.right + "," + dirty.bottom + "} surface="
+ surface + " surface.isValid()=" + surface.isValid() + ", appScale:" +
appScale + ", width=" + mWidth + ", height=" + mHeight);
}
mAttachInfo.mTreeObserver.dispatchOnDraw();
int xOffset = -mCanvasOffsetX;
int yOffset = -mCanvasOffsetY + curScrollY;
final WindowManager.LayoutParams params = mWindowAttributes;
final Rect surfaceInsets = params != null ? params.surfaceInsets : null;
if (surfaceInsets != null) {
xOffset -= surfaceInsets.left;
yOffset -= surfaceInsets.top;
// Offset dirty rect for surface insets.
dirty.offset(surfaceInsets.left, surfaceInsets.right);
}
boolean accessibilityFocusDirty = false;
final Drawable drawable = mAttachInfo.mAccessibilityFocusDrawable;
if (drawable != null) {
final Rect bounds = mAttachInfo.mTmpInvalRect;
final boolean hasFocus = getAccessibilityFocusedRect(bounds);
if (!hasFocus) {
bounds.setEmpty();
}
if (!bounds.equals(drawable.getBounds())) {
accessibilityFocusDirty = true;
}
}
mAttachInfo.mDrawingTime =
mChoreographer.getFrameTimeNanos() / TimeUtils.NANOS_PER_MS;
boolean useAsyncReport = false;
if (!dirty.isEmpty() || mIsAnimating || accessibilityFocusDirty) {
if (mAttachInfo.mThreadedRenderer != null && mAttachInfo.mThreadedRenderer.isEnabled()) {
//硬件加速
// If accessibility focus moved, always invalidate the root.
boolean invalidateRoot = accessibilityFocusDirty || mInvalidateRootRequested;
mInvalidateRootRequested = false;
// Draw with hardware renderer.
mIsAnimating = false;
if (mHardwareYOffset != yOffset || mHardwareXOffset != xOffset) {
mHardwareYOffset = yOffset;
mHardwareXOffset = xOffset;
invalidateRoot = true;
}
if (invalidateRoot) {
mAttachInfo.mThreadedRenderer.invalidateRoot();
}
dirty.setEmpty();
final boolean updated = updateContentDrawBounds();
if (mReportNextDraw) {
// report next draw overrides setStopped()
// This value is re-sync'd to the value of mStopped
// in the handling of mReportNextDraw post-draw.
mAttachInfo.mThreadedRenderer.setStopped(false);
}
if (updated) {
requestDrawWindow();
}
useAsyncReport = true;
//硬件加速绘制
mAttachInfo.mThreadedRenderer.draw(mView, mAttachInfo, this);
} else {
// eglTerminate() for instance.
if (mAttachInfo.mThreadedRenderer != null &&
!mAttachInfo.mThreadedRenderer.isEnabled() &&
mAttachInfo.mThreadedRenderer.isRequested() &&
mSurface.isValid()) {
try {
mAttachInfo.mThreadedRenderer.initializeIfNeeded(
mWidth, mHeight, mAttachInfo, mSurface, surfaceInsets);
} catch (OutOfResourcesException e) {
handleOutOfResourcesException(e);
return false;
}
mFullRedrawNeeded = true;
scheduleTraversals();
return false;
}
//软件绘制
if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset,
scalingRequired, dirty, surfaceInsets)) {
return false;
}
}
}
if (animating) {
mFullRedrawNeeded = true;
scheduleTraversals();
}
return useAsyncReport;
}
软硬件绘制对比
调用 ViewRootImpl#drawSoftware 进行软件绘制
private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
boolean scalingRequired, Rect dirty, Rect surfaceInsets) {
// 通过dirty区域，获取并锁定canvas，后续传给decorView
final Canvas canvas;
int dirtyXOffset = xoff;
int dirtyYOffset = yoff;
if (surfaceInsets != null) {
dirtyXOffset += surfaceInsets.left;
dirtyYOffset += surfaceInsets.top;
}
try {
dirty.offset(-dirtyXOffset, -dirtyYOffset);
final int left = dirty.left;
final int top = dirty.top;
final int right = dirty.right;
final int bottom = dirty.bottom;
canvas = mSurface.lockCanvas(dirty);
// TODO: Do this in native
canvas.setDensity(mDensity);
}
try {
if (DEBUG_ORIENTATION || DEBUG_DRAW) {
Log.v(mTag, "Surface " + surface + " drawing to bitmap w="
+ canvas.getWidth() + ", h=" + canvas.getHeight());
//canvas.drawARGB(255, 255, 0, 0);
}
// left in the blank areas.
if (!canvas.isOpaque() || yoff != 0 || xoff != 0) {
canvas.drawColor(0, PorterDuff.Mode.CLEAR);
}
dirty.setEmpty();
mIsAnimating = false;
mView.mPrivateFlags |= View.PFLAG_DRAWN;
}
//画布平移
canvas.translate(-xoff, -yoff);
if (mTranslator != null) {
mTranslator.translateCanvas(canvas);
}
canvas.setScreenDensity(scalingRequired ? mNoncompatDensity : 0);
//调用 View 的 draw
mView.draw(canvas);
drawAccessibilityFocusedDrawableIfNeeded(canvas);
}
return true;
}
接下来我们看View的draw方法，的绘制过程
public void draw(Canvas canvas) {
final int privateFlags = mPrivateFlags;
//将flag22位21位设置为off，并且将PFLAG_DRAWN设置为on
mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;
/*
*
* 1. Draw the background
* 2. If necessary, save the canvas' layers to prepare for fading
* 3. Draw view's content
* 4. Draw children
* 5. If necessary, draw the fading edges and restore layers
* 6. Draw decorations (scrollbars for instance)
* 7. If necessary, draw the default focus highlight
*/
// Step 1, draw the background, if needed
//绘制背景
int saveCount;
drawBackground(canvas);
// skip step 2 & 5 if possible (common case)
// 大多数情况(不需要绘制边界阴影的情况)都不需要2和5这两部，跳过
final int viewFlags = mViewFlags;
// 是否需要绘制横向边界阴影
boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
// 是否需要绘制竖向向边界阴影
boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
// 不需要绘制横向和竖向阴影，执行3，4，6步
if (!verticalEdges && !horizontalEdges) {
// Step 3, draw the content
onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
drawAutofilledHighlight(canvas);
// Overlay is part of the content and draws beneath Foreground
if (mOverlay != null && !mOverlay.isEmpty()) {
mOverlay.getOverlayView().dispatchDraw(canvas);
}
// Step 6, draw decorations (foreground, scrollbars)
onDrawForeground(canvas);
// Step 7, draw the default focus highlight
drawDefaultFocusHighlight(canvas);
if (isShowingLayoutBounds()) {
debugDrawFocus(canvas);
}
// we're done...
return;
}
/*
* Here we do the full fledged routine...
* (this is an uncommon case where speed matters less,
* this is why we repeat some of the tests that have been
* done above)
*/
// 需要绘制阴影的话，则执行全部2-6的流程，不过这个流程并不常见，而且性能和速度上也不是很优秀。
boolean drawTop = false;
boolean drawBottom = false;
boolean drawLeft = false;
boolean drawRight = false;
float topFadeStrength = 0.0f;
float bottomFadeStrength = 0.0f;
float leftFadeStrength = 0.0f;
float rightFadeStrength = 0.0f;
// Step 2, save the canvas' layers
//保存fading相关的canvas图层信息
int paddingLeft = mPaddingLeft;
final boolean offsetRequired = isPaddingOffsetRequired();
if (offsetRequired) {
paddingLeft += getLeftPaddingOffset();
}
int left = mScrollX + paddingLeft;
int right = left + mRight - mLeft - mPaddingRight - paddingLeft;
int top = mScrollY + getFadeTop(offsetRequired);
int bottom = top + getFadeHeight(offsetRequired);
if (offsetRequired) {
right += getRightPaddingOffset();
bottom += getBottomPaddingOffset();
}
final ScrollabilityCache scrollabilityCache = mScrollCache;
final float fadeHeight = scrollabilityCache.fadingEdgeLength;
int length = (int) fadeHeight;
// clip the fade length if top and bottom fades overlap
// overlapping fades produce odd-looking artifacts
if (verticalEdges && (top + length > bottom - length)) {
length = (bottom - top) / 2;
}
// also clip horizontal fades if necessary
if (horizontalEdges && (left + length > right - length)) {
length = (right - left) / 2;
}
if (verticalEdges) {
topFadeStrength = Math.max(0.0f, Math.min(1.0f, getTopFadingEdgeStrength()));
drawTop = topFadeStrength * fadeHeight > 1.0f;
bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, getBottomFadingEdgeStrength()));
drawBottom = bottomFadeStrength * fadeHeight > 1.0f;
}
if (horizontalEdges) {
leftFadeStrength = Math.max(0.0f, Math.min(1.0f, getLeftFadingEdgeStrength()));
drawLeft = leftFadeStrength * fadeHeight > 1.0f;
rightFadeStrength = Math.max(0.0f, Math.min(1.0f, getRightFadingEdgeStrength()));
drawRight = rightFadeStrength * fadeHeight > 1.0f;
}
saveCount = canvas.getSaveCount();
int topSaveCount = -1;
int bottomSaveCount = -1;
int leftSaveCount = -1;
int rightSaveCount = -1;
int solidColor = getSolidColor();
if (solidColor == 0) {
if (drawTop) {
topSaveCount = canvas.saveUnclippedLayer(left, top, right, top + length);
}
if (drawBottom) {
bottomSaveCount = canvas.saveUnclippedLayer(left, bottom - length, right, bottom);
}
if (drawLeft) {
leftSaveCount = canvas.saveUnclippedLayer(left, top, left + length, bottom);
}
if (drawRight) {
rightSaveCount = canvas.saveUnclippedLayer(right - length, top, right, bottom);
}
} else {
scrollabilityCache.setFadeColor(solidColor);
}
// Step 3, draw the content 调用onDraw方法进行绘制
onDraw(canvas);
// Step 4, draw the children 调用dispatchDraw方法，绘制子View
dispatchDraw(canvas);
// Step 5, draw the fade effect and restore layers
//绘制阴影边缘
final Paint p = scrollabilityCache.paint;
final Matrix matrix = scrollabilityCache.matrix;
final Shader fade = scrollabilityCache.shader;
// must be restored in the reverse order that they were saved
if (drawRight) {
matrix.setScale(1, fadeHeight * rightFadeStrength);
matrix.postRotate(90);
matrix.postTranslate(right, top);
fade.setLocalMatrix(matrix);
p.setShader(fade);
if (solidColor == 0) {
canvas.restoreUnclippedLayer(rightSaveCount, p);
} else {
canvas.drawRect(right - length, top, right, bottom, p);
}
}
if (drawLeft) {
matrix.setScale(1, fadeHeight * leftFadeStrength);
matrix.postRotate(-90);
matrix.postTranslate(left, top);
fade.setLocalMatrix(matrix);
p.setShader(fade);
if (solidColor == 0) {
canvas.restoreUnclippedLayer(leftSaveCount, p);
} else {
canvas.drawRect(left, top, left + length, bottom, p);
}
}
if (drawBottom) {
matrix.setScale(1, fadeHeight * bottomFadeStrength);
matrix.postRotate(180);
matrix.postTranslate(left, bottom);
fade.setLocalMatrix(matrix);
p.setShader(fade);
if (solidColor == 0) {
canvas.restoreUnclippedLayer(bottomSaveCount, p);
} else {
canvas.drawRect(left, bottom - length, right, bottom, p);
}
}
if (drawTop) {
matrix.setScale(1, fadeHeight * topFadeStrength);
matrix.postTranslate(left, top);
fade.setLocalMatrix(matrix);
p.setShader(fade);
if (solidColor == 0) {
canvas.restoreUnclippedLayer(topSaveCount, p);
} else {
canvas.drawRect(left, top, right, top + length, p);
}
}
canvas.restoreToCount(saveCount);
drawAutofilledHighlight(canvas);
// Overlay is part of the content and draws beneath Foreground
// 绘制覆盖物，这个覆盖物在前景图的下面（API18引入）
if (mOverlay != null && !mOverlay.isEmpty()) {
mOverlay.getOverlayView().dispatchDraw(canvas);
}
// Step 6, draw decorations (foreground, scrollbars) 绘制前景图
onDrawForeground(canvas);
// Step 7, draw the default focus highlight 高亮
drawDefaultFocusHighlight(canvas);
if (isShowingLayoutBounds()) {
debugDrawFocus(canvas);
}
}
- drawBackground
private void drawBackground(Canvas canvas) {
final Drawable background = mBackground;
if (background == null) {
return;
}
//如果背景边界发生变化，则重新设置边界大小
setBackgroundBounds();
//如果设置了硬件加速，则使用 display list 绘制背景
if (canvas.isHardwareAccelerated() && mAttachInfo != null
&& mAttachInfo.mThreadedRenderer != null) {
mBackgroundRenderNode = getDrawableRenderNode(background, mBackgroundRenderNode);
final RenderNode renderNode = mBackgroundRenderNode;
if (renderNode != null && renderNode.hasDisplayList()) {
setBackgroundRenderNodeProperties(renderNode);
((RecordingCanvas) canvas).drawRenderNode(renderNode);
return;
}
}
//获取滑动偏移量，如果有偏移，则先把canvas移动，然后绘制背景，最后再移动回来
final int scrollX = mScrollX;
final int scrollY = mScrollY;
if ((scrollX | scrollY) == 0) {
background.draw(canvas);
} else {
canvas.translate(scrollX, scrollY);
background.draw(canvas);
canvas.translate(-scrollX, -scrollY);
}
}
- onDrawForeground
public void onDrawForeground(Canvas canvas) {
onDrawScrollIndicators(canvas);
onDrawScrollBars(canvas);
final Drawable foreground = mForegroundInfo != null ? mForegroundInfo.mDrawable : null;
if (foreground != null) {
if (mForegroundInfo.mBoundsChanged) {
mForegroundInfo.mBoundsChanged = false;
final Rect selfBounds = mForegroundInfo.mSelfBounds;
final Rect overlayBounds = mForegroundInfo.mOverlayBounds;
if (mForegroundInfo.mInsidePadding) {
selfBounds.set(0, 0, getWidth(), getHeight());
} else {
selfBounds.set(getPaddingLeft(), getPaddingTop(),
getWidth() - getPaddingRight(), getHeight() - getPaddingBottom());
}
final int ld = getLayoutDirection();
Gravity.apply(mForegroundInfo.mGravity, foreground.getIntrinsicWidth(),
foreground.getIntrinsicHeight(), selfBounds, overlayBounds, ld);
foreground.setBounds(overlayBounds);
}
foreground.draw(canvas);
}
}
三、UI 刷新
UI 刷新只能在主线程进行吗？
答案：不是，是可以在子线程中刷新的。那为什么我们在开发中在子线程中刷新UI报错？
造成这个原因主要是ViewRootImpl创建是在mainThread中创建的，在里面invalidateChildInParent()方法会做checkThread()校验，当不是在创建线程中刷新就抛出异常。校验代码
ViewRootImpl#checkThread
void checkThread() {
if (mThread != Thread.currentThread()) {
throw new CalledFromWrongThreadException(
"Only the original thread that created a view hierarchy can touch its views.");
}
}
3.1、刷新过程
首先我们调用VIew 的 invalidate()方法进行UI刷新
public void invalidate() {
invalidate(true);
}
public void invalidate(boolean invalidateCache) {
invalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true);
}
void invalidateInternal(int l, int t, int r, int b, boolean invalidateCache,
boolean fullInvalidate) {
if (mGhostView != null) {
mGhostView.invalidate(true);
return;
}
if (skipInvalidate()) {
return;
}
// Reset content capture caches
mPrivateFlags4 &= ~PFLAG4_CONTENT_CAPTURE_IMPORTANCE_MASK;
mContentCaptureSessionCached = false;
if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)
|| (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID)
|| (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED
|| (fullInvalidate && isOpaque() != mLastIsOpaque)) {
if (fullInvalidate) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~PFLAG_DRAWN;
}
mPrivateFlags |= PFLAG_DIRTY;
if (invalidateCache) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
// Propagate the damage rectangle to the parent view.
final AttachInfo ai = mAttachInfo;
//父视图
final ViewParent p = mParent;
if (p != null && ai != null && l < r && t < b) {
final Rect damage = ai.mTmpInvalRect;
damage.set(l, t, r, b);
//调用俯视图(就是外部试图)刷新
p.invalidateChild(this, damage);
}
// Damage the entire projection receiver, if necessary.
if (mBackground != null && mBackground.isProjected()) {
final View receiver = getProjectionReceiver();
if (receiver != null) {
receiver.damageInParent();
}
}
}
}
在执行p.invalidateChild(this, damage);方法，会执行ViewGroup 的invalidateChild方法。
public final void invalidateChild(View child, final Rect dirty) {
// attachInfo 保存当前窗口的一些信息
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null && attachInfo.mHardwareAccelerated) {
// HW accelerated fast path
onDescendantInvalidated(child, child);
return;
}
ViewParent parent = this;
if (attachInfo != null) {
//如果子视图正在做动画的话，我们想复制这个标记到我们自己以及父视图来确保这个无效请求的过程
//判断是否要正在或者下次绘制要做动画。子视图的mPrivateFlags会包含DRAW_ANIMATION标志位。
final boolean drawAnimation = (child.mPrivateFlags & PFLAG_DRAW_ANIMATION) != 0;
Matrix childMatrix = child.getMatrix();
if (child.mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
//获取子视图的布局坐标
final int[] location = attachInfo.mInvalidateChildLocation;
location[CHILD_LEFT_INDEX] = child.mLeft;
location[CHILD_TOP_INDEX] = child.mTop;
if (!childMatrix.isIdentity() ||
(mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
Matrix transformMatrix;
if ((mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) {
Transformation t = attachInfo.mTmpTransformation;
boolean transformed = getChildStaticTransformation(child, t);
if (transformed) {
transformMatrix = attachInfo.mTmpMatrix;
transformMatrix.set(t.getMatrix());
if (!childMatrix.isIdentity()) {
transformMatrix.preConcat(childMatrix);
}
} else {
transformMatrix = childMatrix;
}
} else {
transformMatrix = childMatrix;
}
transformMatrix.mapRect(boundingRect);
dirty.set((int) Math.floor(boundingRect.left),
(int) Math.floor(boundingRect.top),
(int) Math.ceil(boundingRect.right),
(int) Math.ceil(boundingRect.bottom));
}
do {
View view = null;
if (parent instanceof View) {
view = (View) parent;
}
if (drawAnimation) {
//如果父视图不为空
if (view != null) {
view.mPrivateFlags |= PFLAG_DRAW_ANIMATION;
} else if (parent instanceof ViewRootImpl) {
//如果父视图为ViewRoot，就设置ViewRoot的mIsAnimating变量为true。
((ViewRootImpl) parent).mIsAnimating = true;
}
}
// 如果父视图是包含 DIRTY_OPAQUE 或者 NOT_DIRTY 属性的，标记父视图为DIRTY_OPAQUE 属性。
// 该属性是来自于发起 invalidate()的那个子视图。
// 如果父视图不为空，并且父视图的逻辑变量的 DIRTY 属性位不是 DIRTY（只要父视图不完全绘制，子视图为不透明的）
if (view != null) {
//设置当前视图的父视图的逻辑变量为 opaqueFlag 变量保存的属性，该属性有两种可能。
//如果当前视图的子视图是不透明的，则当前视图的父视图的dirty标志位的属性为DIRTY_OPAQUE，当前视图的父视图可以不重绘，因为子视图是不透明的。
//如果当前视图的子视图是透明的，则当前视图的父视图的dirty标志位的属性为 DIRTY。
if ((view.mPrivateFlags & PFLAG_DIRTY_MASK) != PFLAG_DIRTY) {
view.mPrivateFlags = (view.mPrivateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DIRTY;
}
}
//更新parent变量，invalidateChildInParent()的返回值进行递归调用。
//location为当前ViewGroup的视图坐标，dirty为当前视图的子视图需要重绘的区域Rect。
parent = parent.invalidateChildInParent(location, dirty);
if (view != null) {
// Account for transform on current parent
Matrix m = view.getMatrix();
if (!m.isIdentity()) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
m.mapRect(boundingRect);
dirty.set((int) Math.floor(boundingRect.left),
(int) Math.floor(boundingRect.top),
(int) Math.ceil(boundingRect.right),
(int) Math.ceil(boundingRect.bottom));
}
}
//循环到View树的根视图即退出
} while (parent != null);
}
}
掉parent.invalidateChildInParent()最终会调到ViewRootImpl中的invalidateChildInParent方法，因为ViewRootImpl是实际操作者，操作自己的窗口的，也就是最终的根。
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
//确保主线程调用，否则直接抛出异常
checkThread();
if (DEBUG_DRAW) Log.v(mTag, "Invalidate child: " + dirty);
if (dirty == null) {
//绘制
invalidate();
return null;
} else if (dirty.isEmpty() && !mIsAnimating) {
return null;
}
//如果当前显示区域有Y轴偏移，或者有 mTranslator 转换器
if (mCurScrollY != 0 || mTranslator != null) {
mTempRect.set(dirty);
//将dirty的引用指向mTempRect，该区域为实际绘制的区域。
dirty = mTempRect;
//如果Y轴有偏移量，就设置dirty的偏移量进行调整。
if (mCurScrollY != 0) {
dirty.offset(0, -mCurScrollY);
}
//处理逻辑像素转换
if (mTranslator != null) {
mTranslator.translateRectInAppWindowToScreen(dirty);
}
//如果有缩放的需要的话，就将dirty区域进行1像素的内嵌。
if (mAttachInfo.mScalingRequired) {
dirty.inset(-1, -1);
}
}
invalidateRectOnScreen(dirty);
return null;
}
checkThread()校验当前线程是否是创建时的线程mThread,不是抛出异常。这就是在非UI线程刷新报错的原因。
void checkThread() {
if (mThread != Thread.currentThread()) {
throw new CalledFromWrongThreadException(
"Only the original thread that created a view hierarchy can touch its views.");
}
}
执行ViewRootImpl#invalidate()绘制
void invalidate() {
// mDirty 为脏区域，就是UI改变的区域
mDirty.set(0, 0, mWidth, mHeight);
// 查看是否刚刚发送过请求，也就是之前发送的请求未处理。
if (!mWillDrawSoon) {
//检测 mTraversalScheduled 变量。
scheduleTraversals();
}
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
//开启同步屏障
//利用了同步同步屏障，同步屏障内容见 Handler 篇
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
//发送异步消息
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
postCallback() 最终走到了 Choreographer#postCallbackDelayedInternal()：
@UnsupportedAppUsage
@TestApi
public void postCallback(int callbackType, Runnable action, Object token) {
postCallbackDelayed(callbackType, action, token, 0);
}
@UnsupportedAppUsage
@TestApi
public void postCallbackDelayed(int callbackType,
Runnable action, Object token, long delayMillis) {
if (action == null) {
throw new IllegalArgumentException("action must not be null");
}
if (callbackType < 0 || callbackType > CALLBACK_LAST) {
throw new IllegalArgumentException("callbackType is invalid");
}
postCallbackDelayedInternal(callbackType, action, token, delayMillis);
}
private void postCallbackDelayedInternal(int callbackType,
Object action, Object token, long delayMillis) {
if (DEBUG_FRAMES) {
Log.d(TAG, "PostCallback: type=" + callbackType
+ ", action=" + action + ", token=" + token
+ ", delayMillis=" + delayMillis);
}
synchronized (mLock) {
final long now = SystemClock.uptimeMillis();
final long dueTime = now + delayMillis;
mCallbackQueues[callbackType].addCallbackLocked(dueTime, action, token);
if (dueTime <= now) {
scheduleFrameLocked(now);
} else {
Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_CALLBACK, action);
msg.arg1 = callbackType;
msg.setAsynchronous(true); //异步消息
mHandler.sendMessageAtTime(msg, dueTime); //发送消息
}
}
}
这里就开启了同步屏障，并发送异步消息，由于 UI 更新相关的消息是优先级最高的，这样系统就会优先处理这些异步消息
最后，当要移除同步屏障的时候需要调用 ViewRootImpl#unscheduleTraversals()
void unscheduleTraversals() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
//移除同步屏障
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
mChoreographer.removeCallbacks(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
}
}
- 综上可得最终UI的刷新在主线程中完成，并需要 Handler 发送更新UI。可见 Handler 在的重要性。
3.2、在子线程刷新UI
- 要是想着子线程中刷新UI，我们可以在子线程中创建
ViewRootImpl就可以避免checkThread()时发生异常
public class MainActivity extends AppCompatActivity {
private static final String TAG = "leo";
private TextView mTextView;
private static final int OVERLAY_PERMISSION_CODE = 1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//也可以更新 UI ，因为此时ViewRootImpl还没有创建
new Thread(new Runnable() {
@Override
public void run() {
mTextView.setText("aaa");
}
}).start();
// 设置权限
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (!Settings.canDrawOverlays(this)) {
Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.parse("package:" + getPackageName()));
startActivityForResult(intent, OVERLAY_PERMISSION_CODE);
}
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == OVERLAY_PERMISSION_CODE) {
if (Settings.canDrawOverlays(this)) {
// 1-2.在子线程中创建ViewRootImpl
childThreadChangeUI();
} else {
}
}
}
public void childThreadChangeUI() {
new Thread() {
@RequiresApi(api = Build.VERSION_CODES.R)
@Override
public void run() {
Looper.prepare();
WindowManager wm = (WindowManager) getApplicationContext().getSystemService(WINDOW_SERVICE);
View view = View.inflate(MainActivity.this, R.layout.item, null);
TextView tv = view.findViewById(R.id.tv);
WindowManager.LayoutParams params = new WindowManager.LayoutParams();
params.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
// 设置不拦截焦点
params.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL;
params.width = (int) (60 * getResources().getDisplayMetrics().density);
params.height = (int) (60 * getResources().getDisplayMetrics().density);
params.gravity = Gravity.LEFT | Gravity.TOP;// 且设置坐标系 左上角
params.format = PixelFormat.TRANSPARENT;
int width = wm.getDefaultDisplay().getWidth();
int height = wm.getDefaultDisplay().getHeight();
params.y = height / 2 - params.height / 2;
wm.addView(view, params);
view.setOnTouchListener(new View.OnTouchListener() {
private int y;
private int x;
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
x = (int) event.getRawX();
y = (int) event.getRawY();
break;
case MotionEvent.ACTION_MOVE:
int minX = (int) (event.getRawX() - x);
int minY = (int) (event.getRawY() - y);
params.x = Math.min(width - params.width, Math.max(0, minX + params.x));
params.y = Math.min(height - params.height, Math.max(0, minY + params.y));
wm.updateViewLayout(view, params);
x = (int) event.getRawX();
y = (int) event.getRawY();
break;
case MotionEvent.ACTION_UP:
if (params.x > 0 && params.x < width - params.width) {
int x = params.x;
if (x > (width - params.width) / 2) {
params.x = width - params.width;
} else {
params.x = 0;
}
wm.updateViewLayout(view, params);
} else if (params.x == 0 || params.x == (width - params.width)) {
Toast.makeText(MainActivity.this, "被电击了", Toast.LENGTH_SHORT).show();
tv.setText("更改了item的TextView值");
}
break;
}
return true;
}
});
Looper.loop();
}
}.start();
}
}
- 在 AndroidManifest 导入权限