Android绘制源码分析上介绍了这个屏幕的架构，以及相关的系统类Android绘制源码分析中介绍了整个绘制的启动，绘制过程 ，绘制 完毕的一个流程，这篇的终点就是介绍我们平常自定的三步骤
image.png
View的生命周期
image.png
1.创建Activity时View的状态
image.png
2.退出Activity时View的状态
image.png
3.按住Home键时View的状态
image.png
生命周期介绍
- onFinishInflate() 当View中所有的子控件均被映射成xml后触发
- onMeasure( int , int ) 确定所有子元素的大小
- onLayout( boolean , int , int , int , int ) 当View分配所有的子元素的大小和位置时触发
- onSizeChanged( int , int , int , int ) 当view的大小发生变化时触发
- onDraw(Canvas) view渲染内容的细节
- onKeyDown( int , KeyEvent) 有按键按下后触发
- onKeyUp( int , KeyEvent) 有按键按下后弹起时触发
- onTrackballEvent(MotionEvent) 轨迹球事件
- onTouchEvent(MotionEvent) 触屏事件
- onFocusChanged( boolean , int , Rect) 当View获取或失去焦点时触发
- onWindowFocusChanged( boolean ) 当窗口包含的view获取或失去焦点时触发
- onAttachedToWindow() 当view被附着到一个窗口时触发
- onDetachedFromWindow() 当view离开附着的窗口时触发，Android123提示该方法和 onAttachedToWindow() 是相反的。
- onWindowVisibilityChanged( int ) 当窗口中包含的可见的view发生变化时触发
1.View确定大小
如何确定大小？肯定就需要测量，从根 View 递归调用每一级子 View 的 measure() 方法，对它们进行测量。
所以测量是指父View对子View测量，父View收到子View宽高参数，然后结合自身的宽高，一起商量测量出给宽高传递给子View
- 测量情况一
ViewRootImpl
int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
private static int getRootMeasureSpec(int windowSize, int rootDimension) {
int measureSpec;
switch (rootDimension) {
case ViewGroup.LayoutParams.MATCH_PARENT:
// Window can't resize. Force root view to be windowSize.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
break;
case ViewGroup.LayoutParams.WRAP_CONTENT:
// Window can resize. Set max size for root view.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
break;
default:
// Window wants to be an exact size. Force root view to be that size.
measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
break;
}
return measureSpec;
}
- 测量情况二
ViewRootImpl
if (lp.horizontalWeight > 0.0f) {
width += (int) ((mWidth - width) * lp.horizontalWeight);
childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(width,
MeasureSpec.EXACTLY);
measureAgain = true;
}
if (lp.verticalWeight > 0.0f) {
height += (int) ((mHeight - height) * lp.verticalWeight);
childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height,
MeasureSpec.EXACTLY);
measureAgain = true;
}
public static int makeMeasureSpec(@IntRange(from = 0, to = (1 << MeasureSpec.MODE_SHIFT) - 1) int size,
@MeasureSpecMode int mode) {
if (sUseBrokenMakeMeasureSpec) {
return size + mode;
} else {
return (size & ~MODE_MASK) | (mode & MODE_MASK);
}
}
- 传递给子View mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
boolean optical = isLayoutModeOptical(this);
if (optical != isLayoutModeOptical(mParent)) {
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);
}
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) {
// measure ourselves, this should set the measured dimension flag back
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
setMeasuredDimensionRaw((int) (value >> 32), (int) value);
mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
}
}
mOldWidthMeasureSpec = widthMeasureSpec;
mOldHeightMeasureSpec = heightMeasureSpec;
}
- 通过onMeasure父view告诉子View的宽高和测量的模式
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
- 子类拿到父类给的高度后，可能需要重新要求高度，但是高度是由父类共同决定，所以需要校验自己设定的高度合不合理
public static
int resolveSizeAndState(int size, int measureSpec, int childMeasuredState) {
final int specMode = MeasureSpec.getMode(measureSpec);
final int specSize = MeasureSpec.getSize(measureSpec);
final int result;
switch (specMode) {
case MeasureSpec.AT_MOST:
if (specSize < size) {
result = specSize | MEASURED_STATE_TOO_SMALL;
} else {
result = size;
}
break;
case MeasureSpec.EXACTLY:
result = specSize;
break;
case MeasureSpec.UNSPECIFIED:
default:
result = size;
}
return result | (childMeasuredState & MEASURED_STATE_MASK);
}
2.确定子View位置onLayout()
performLayout(lp, mWidth, mHeight);
private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
int desiredWindowHeight) {
final View host = mView;
try {
host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
........................................................
}
}
host 就是DecorView，host.layout确定自身的位置
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) {
onLayout(changed, l, t, r, b);
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);
}
}
}
}
setFrame(l, t, r, b)这个方法用于确认View四个点的位置，及初始化left,top，right，bottom的位置，这是ViewGroup布局完成
protected boolean setFrame(int left, int top, int right, int bottom) {
boolean changed = false;
if (DBG) {
Log.d(VIEW_LOG_TAG, this + " View.setFrame(" + left + "," + top + ","
+ right + "," + bottom + ")");
}
if (mLeft != left || mRight != right || mTop != top || mBottom != bottom) {
changed = true;
// Remember our drawn bit
int drawn = mPrivateFlags & PFLAG_DRAWN;
int oldWidth = mRight - mLeft;
int oldHeight = mBottom - mTop;
int newWidth = right - left;
int newHeight = bottom - top;
boolean sizeChanged = (newWidth != oldWidth) || (newHeight != oldHeight);
// Invalidate our old position
invalidate(sizeChanged);
mLeft = left;
mTop = top;
mRight = right;
mBottom = bottom;
mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom);
mPrivateFlags |= PFLAG_HAS_BOUNDS;
if (sizeChanged) {
sizeChange(newWidth, newHeight, oldWidth, oldHeight);
}
if ((mViewFlags & VISIBILITY_MASK) == VISIBLE || mGhostView != null) {
// If we are visible, force the DRAWN bit to on so that
// this invalidate will go through (at least to our parent).
// This is because someone may have invalidated this view
// before this call to setFrame came in, thereby clearing
// the DRAWN bit.
mPrivateFlags |= PFLAG_DRAWN;
invalidate(sizeChanged);
// parent display list may need to be recreated based on a change in the bounds
// of any child
invalidateParentCaches();
}
}
return changed;
}
mRenderNode.setLeftTopRightBottom(mLeft, mTop, mRight, mBottom);原来这个就是设置View位置的最终方法，点进去就是native代码了
sizeChange(newWidth, newHeight, oldWidth, oldHeight);这个就是回调给子类确定最终宽高的onSizeChanged(newWidth, newHeight, oldWidth, oldHeight)
以上就是确定View位置的大概方法和流程
3.开始绘制ViewRootlmpl->draw
performDraw()
private void performDraw() {
if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) {
return;
} else if (mView == null) {
return;
}
//TODO 省略
try {
boolean canUseAsync = draw(fullRedrawNeeded);
if (usingAsyncReport && !canUseAsync) {
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback(null);
usingAsyncReport = false;
}
} finally {
mIsDrawing = false;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
//TODO 省略
ViewRootlmpl->boolean canUseAsync = draw(fullRedrawNeeded);
private boolean draw(boolean fullRedrawNeeded) {
Surface surface = mSurface;
if (!surface.isValid()) {
return false;
}
//TODO 省略
if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset,
scalingRequired, dirty, surfaceInsets)) {
return false;
}
}
}
//TODO 省略
}
ViewRootlmpl->drawSoftware()
private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
boolean scalingRequired, Rect dirty, Rect surfaceInsets) {
// Draw with software renderer.
final Canvas canvas;
try {
canvas = mSurface.lockCanvas(dirty);
try {
if (!canvas.isOpaque() || yoff != 0 || xoff != 0) {
canvas.drawColor(0, PorterDuff.Mode.CLEAR);
}
dirty.setEmpty();
mIsAnimating = false;
mView.mPrivateFlags |= View.PFLAG_DRAWN;
try {
mView.draw(canvas);
drawAccessibilityFocusedDrawableIfNeeded(canvas);
}
}
return true;
}
canvas 是由图表Surface 赋值传值给 mView.draw(canvas);
View->draw()
public void draw(Canvas canvas) {
if (!dirtyOpaque) {
drawBackground(canvas);
}
if (!verticalEdges && !horizontalEdges) {
// Step 3, draw the content
if (!dirtyOpaque) 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);
int solidColor = getSolidColor();
if (solidColor == 0) {
if (drawTop) {
canvas.saveUnclippedLayer(left, top, right, top + length);
}
if (drawBottom) {
canvas.saveUnclippedLayer(left, bottom - length, right, bottom);
}
if (drawLeft) {
canvas.saveUnclippedLayer(left, top, left + length, bottom);
}
if (drawRight) {
canvas.saveUnclippedLayer(right - length, top, right, bottom);
}
} else {
scrollabilityCache.setFadeColor(solidColor);
}
// Step 3, draw the content
if (!dirtyOpaque) onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
// Step 6, draw decorations (foreground, scrollbars)
onDrawForeground(canvas);
}
最后由子类在onDraw(）自定义绘制
总结一下自定义控件吧，自定义控件分几种
1.单独一个子控件，我的目的就是绘制，所以重点就是draw里面的逻辑，不需要去管layout,或者measure
2.自定义时,里面包含多个控件，这时需要去测量 （measure），布局（layout），绘制（draw）
3.自定义时明确功能,可能只是需要在TextView中加一个功能，所以可以直接继承TextView
3.自定义时可能是父布局里，如RelativeLayout，只是需要改变某个需求，可以直接继承RelativeLayout
4.自定义组合控件，某个布局块的一部分控件采用父控件统一管理