本系列博客基于android-28版本
【Window系列】——Toast源码解析
【Window系列】——PopupWindow的前世今生
【Window系列】——Dialog源码解析
前言
上一篇博客分析了Toast的源码，一提到Window必然少不了本篇博客分析的PopupWindow，本来我以为是一样的流程，创建Window，设置View到DecorView，加入Window，完事儿...但却发现PopupWindow却没有按照这种实现方式实现的。
大纲
本篇博客会分析一下几点：
- PopupWindow的实现原理源码
- PopupWindow关于BackgroundDrawable的版本差异导致的问题
- PopupWindow的触摸事件处理
源码分析
我们平时使用PopupWindow主要涉及以下三个核心方法：
PopupWindow window = new PopupWindow();
window.setContentView(...);
window.showAsDropDown(...);
所以首先看一下构造函数
public PopupWindow(View contentView, int width, int height, boolean focusable) {
if (contentView != null) {
mContext = contentView.getContext();
mWindowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
}
setContentView(contentView);
setWidth(width);
setHeight(height);
setFocusable(focusable);
}
如果在构造函数设置了ContentView，那么直接获取Context对象和WindowManager，调用setContentView方法，设置宽高，和Focusable,这里要注意一下Focusable这个变量，后面会讲到这个变量在PopupWindow中的作用。
如果我们调用的是最基础的构造函数，一般我们下一步会调用setContentView方法设置我们的布局，那么这里我们就来看一下这个方法。
public void setContentView(View contentView) {
if (isShowing()) {
return;
}
//保存ContentView
mContentView = contentView;
if (mContext == null && mContentView != null) {
mContext = mContentView.getContext();
}
if (mWindowManager == null && mContentView != null) {
mWindowManager = (WindowManager) mContext.getSystemService(Context.WINDOW_SERVICE);
}
// Setting the default for attachedInDecor based on SDK version here
// instead of in the constructor since we might not have the context
// object in the constructor. We only want to set default here if the
// app hasn't already set the attachedInDecor.
if (mContext != null && !mAttachedInDecorSet) {
// Attach popup window in decor frame of parent window by default for
// {@link Build.VERSION_CODES.LOLLIPOP_MR1} or greater. Keep current
// behavior of not attaching to decor frame for older SDKs.
setAttachedInDecor(mContext.getApplicationInfo().targetSdkVersion
>= Build.VERSION_CODES.LOLLIPOP_MR1);
}
}
可以看到，和刚才看到的构造函数基本相同，保存了ContentView变量后，获取Context和WindowManger对象。
可以看到上面两个步骤基本上都是做的准备工作，那么接下来看一下最核心的展示方法showAsDropDown
public void showAsDropDown(View anchor) {
showAsDropDown(anchor, 0, 0);
}
public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {
if (isShowing() || !hasContentView()) {
return;
}
TransitionManager.endTransitions(mDecorView);
//绑定监听，设置变量
attachToAnchor(anchor, xoff, yoff, gravity);
mIsShowing = true;
mIsDropdown = true;
//创建布局参数
final WindowManager.LayoutParams p =
createPopupLayoutParams(anchor.getApplicationWindowToken());
//包裹布局，构建布局层级
preparePopup(p);
final boolean aboveAnchor = findDropDownPosition(anchor, p, xoff, yoff,
p.width, p.height, gravity, mAllowScrollingAnchorParent);
updateAboveAnchor(aboveAnchor);
p.accessibilityIdOfAnchor = (anchor != null) ? anchor.getAccessibilityViewId() : -1;
//添加布局到Window中
invokePopup(p);
}
可以看到，这个方法其实还是利用了重载，实现了很多方法，最终都是到了最后这个方法里。
上面大概分了四部分，我分别写了注释，这里来单独看一下。
protected void attachToAnchor(View anchor, int xoff, int yoff, int gravity) {
detachFromAnchor();
final ViewTreeObserver vto = anchor.getViewTreeObserver();
if (vto != null) {
vto.addOnScrollChangedListener(mOnScrollChangedListener);
}
anchor.addOnAttachStateChangeListener(mOnAnchorDetachedListener);
final View anchorRoot = anchor.getRootView();
anchorRoot.addOnAttachStateChangeListener(mOnAnchorRootDetachedListener);
anchorRoot.addOnLayoutChangeListener(mOnLayoutChangeListener);
//弱引用
mAnchor = new WeakReference<>(anchor);
mAnchorRoot = new WeakReference<>(anchorRoot);
mIsAnchorRootAttached = anchorRoot.isAttachedToWindow();
mParentRootView = mAnchorRoot;
mAnchorXoff = xoff;
mAnchorYoff = yoff;
mAnchoredGravity = gravity;
}
可以看到这个方法主要是设置我们传入到参数的，但是这里要注意的是Google在这里使用了弱引用，这个我感觉是比较少见的，目前我所了解的FrameWork层的源码里，很少看到Google使用弱引用，这里利用弱引用保存了传入的布局和顶层父布局。
protected final WindowManager.LayoutParams createPopupLayoutParams(IBinder token) {
final WindowManager.LayoutParams p = new WindowManager.LayoutParams();
// These gravity settings put the view at the top left corner of the
// screen. The view is then positioned to the appropriate location by
// setting the x and y offsets to match the anchor's bottom-left
// corner.
p.gravity = computeGravity();
p.flags = computeFlags(p.flags);
p.type = mWindowLayoutType;
//设置Token
p.token = token;
p.softInputMode = mSoftInputMode;
//设置动画
p.windowAnimations = computeAnimationResource();
if (mBackground != null) {
p.format = mBackground.getOpacity();
} else {
p.format = PixelFormat.TRANSLUCENT;
}
//设置宽高
if (mHeightMode < 0) {
p.height = mLastHeight = mHeightMode;
} else {
p.height = mLastHeight = mHeight;
}
if (mWidthMode < 0) {
p.width = mLastWidth = mWidthMode;
} else {
p.width = mLastWidth = mWidth;
}
p.privateFlags = PRIVATE_FLAG_WILL_NOT_REPLACE_ON_RELAUNCH
| PRIVATE_FLAG_LAYOUT_CHILD_WINDOW_IN_PARENT_FRAME;
// Used for debugging.
p.setTitle("PopupWindow:" + Integer.toHexString(hashCode()));
return p;
}
createPopupLayoutParams是用来创建一个LayoutParam，这里注重注意一下token这个变量，看过前一篇博客的应该都记得，Toast组件也需要一个token变量，这里这个token可以看到是用anchor.getApplicationWindowToken()获取的，也就是父布局的token。关于token后面会抽出一篇博客来专门分析一下，token对于Window类型的影响。
private void preparePopup(WindowManager.LayoutParams p) {
if (mContentView == null || mContext == null || mWindowManager == null) {
throw new IllegalStateException("You must specify a valid content view by "
+ "calling setContentView() before attempting to show the popup.");
}
if (p.accessibilityTitle == null) {
p.accessibilityTitle = mContext.getString(R.string.popup_window_default_title);
}
// The old decor view may be transitioning out. Make sure it finishes
// and cleans up before we try to create another one.
if (mDecorView != null) {
mDecorView.cancelTransitions();
}
// When a background is available, we embed the content view within
// another view that owns the background drawable.
//设置Background包裹
if (mBackground != null) {
mBackgroundView = createBackgroundView(mContentView);
mBackgroundView.setBackground(mBackground);
} else {
mBackgroundView = mContentView;
}
//再用DecorView包裹
mDecorView = createDecorView(mBackgroundView);
mDecorView.setIsRootNamespace(true);
//设置elevation
// The background owner should be elevated so that it casts a shadow.
mBackgroundView.setElevation(mElevation);
// We may wrap that in another view, so we'll need to manually specify
// the surface insets.
p.setSurfaceInsets(mBackgroundView, true /*manual*/, true /*preservePrevious*/);
mPopupViewInitialLayoutDirectionInherited =
(mContentView.getRawLayoutDirection() == View.LAYOUT_DIRECTION_INHERIT);
}
这个方法可以说是popupwindow的最核心的方法了，首先我们可以看到，对mBackgroud变量进行了判空，如果设置了backgroud，则执行createBackgroundView方法。
private PopupBackgroundView createBackgroundView(View contentView) {
final ViewGroup.LayoutParams layoutParams = mContentView.getLayoutParams();
final int height;
if (layoutParams != null && layoutParams.height == WRAP_CONTENT) {
height = WRAP_CONTENT;
} else {
height = MATCH_PARENT;
}
final PopupBackgroundView backgroundView = new PopupBackgroundView(mContext);
final PopupBackgroundView.LayoutParams listParams = new PopupBackgroundView.LayoutParams(
MATCH_PARENT, height);
backgroundView.addView(contentView, listParams);
return backgroundView;
}
这里可以看到，构建了一个宽高相同的布局参数，并且创建了一个PopupBackgroundView，利用addView方法，将我们的ContentView包裹了起来。
private class PopupBackgroundView extends FrameLayout {
public PopupBackgroundView(Context context) {
super(context);
}
@Override
protected int[] onCreateDrawableState(int extraSpace) {
if (mAboveAnchor) {
final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
View.mergeDrawableStates(drawableState, ABOVE_ANCHOR_STATE_SET);
return drawableState;
} else {
return super.onCreateDrawableState(extraSpace);
}
}
}
这里的PopupBackgroundView其实就是一个FrameLayout，单纯的只是为了设置Backgroud。
接下来执行createDecorView方法。
private PopupDecorView createDecorView(View contentView) {
final ViewGroup.LayoutParams layoutParams = mContentView.getLayoutParams();
final int height;
if (layoutParams != null && layoutParams.height == WRAP_CONTENT) {
height = WRAP_CONTENT;
} else {
height = MATCH_PARENT;
}
final PopupDecorView decorView = new PopupDecorView(mContext);
decorView.addView(contentView, MATCH_PARENT, height);
decorView.setClipChildren(false);
decorView.setClipToPadding(false);
return decorView;
}
可以看到和刚才大同小异，哪这回为什么又要包裹一层呢？这里就要看一下PopupDecorView
private class PopupDecorView extends FrameLayout {
/** Runnable used to clean up listeners after exit transition. */
private Runnable mCleanupAfterExit;
public PopupDecorView(Context context) {
super(context);
}
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
//对返回键做了特殊处理
if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
if (getKeyDispatcherState() == null) {
return super.dispatchKeyEvent(event);
}
if (event.getAction() == KeyEvent.ACTION_DOWN && event.getRepeatCount() == 0) {
final KeyEvent.DispatcherState state = getKeyDispatcherState();
if (state != null) {
state.startTracking(event, this);
}
return true;
} else if (event.getAction() == KeyEvent.ACTION_UP) {
final KeyEvent.DispatcherState state = getKeyDispatcherState();
if (state != null && state.isTracking(event) && !event.isCanceled()) {
dismiss();
return true;
}
}
return super.dispatchKeyEvent(event);
} else {
return super.dispatchKeyEvent(event);
}
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mTouchInterceptor != null && mTouchInterceptor.onTouch(this, ev)) {
return true;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
final int x = (int) event.getX();
final int y = (int) event.getY();
if ((event.getAction() == MotionEvent.ACTION_DOWN)
&& ((x < 0) || (x >= getWidth()) || (y < 0) || (y >= getHeight()))) {
//触摸位置在外部，则直接dismiss()
dismiss();
return true;
} else if (event.getAction() == MotionEvent.ACTION_OUTSIDE) {
dismiss();
return true;
} else {
return super.onTouchEvent(event);
}
}
...
}
这里就内容很多了，首先这个还是一个继承了FrameLayout的布局，唯一不同的是，这里重写了两个关键方法dispatchKeyEvent和onTouchEvent，所以我们应该知道这里对键盘事件和触摸事件做了特殊处理，当是返回键时或者触摸位置在View的外部的时候则调用dismiss()方法。
这也就是为什么Popupwindow点击外部可以消失的原因，也就是触摸事件处理。
这里还有一个地方值得我们注意
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mTouchInterceptor != null && mTouchInterceptor.onTouch(this, ev)) {
return true;
}
return super.dispatchTouchEvent(ev);
}
可以看到这里还重写了dispatchTouchEvent方法，熟悉Android事件分发流程的应该清楚，这里是事件分发的顶层，这里多出了一个mTouchInterceptor这个概念，其实就是一个拦截器，也就是说，对于PopupWindow，我们是可以自定义事件的处理的。
做完这所有的准备后，就是最后一个方法了。
private void invokePopup(WindowManager.LayoutParams p) {
if (mContext != null) {
p.packageName = mContext.getPackageName();
}
final PopupDecorView decorView = mDecorView;
decorView.setFitsSystemWindows(mLayoutInsetDecor);
setLayoutDirectionFromAnchor();
//通过WindowManger加入View
mWindowManager.addView(decorView, p);
if (mEnterTransition != null) {
decorView.requestEnterTransition(mEnterTransition);
}
}
终于看到了最核心的显示方法，我们可以确定PopupWindow是通过WindowManger的addView方法加入的。可以发现，其实PopupWindow并没有重新创建新的Window,而是在当前Window上，利用WindowManger.addView加入的。，这可以说就是PopupWindow的显示原理。
PopupWindow关于BackgroundDrawable的版本差异导致的问题
最开始学习PopupWindow的使用方法的时候，我们经常会看到这样的一个注释。
// 如果不设置PopupWindow的背景,就会出现一个问题：无论是点击外部区域还是Back键都无法dismiss弹框
popupWindow.setBackgroundDrawable(new ColorDrawable());
通过上面的源码分析，我们本没有发现BackgroundDrawable会有这么大的影响，只是单纯的印象一个包装View的背景，这里就要说一下PopupWindow的版本差异了，本篇博客是基于android-28,通过源码我们能知道backgrounddrawable不会有这样的影响。但是我们来看一下Android4.2.2的源码
private void preparePopup(WindowManager.LayoutParams p) {
if (mContentView == null || mContext == null || mWindowManager == null) {
throw new IllegalStateException("You must specify a valid content view by "
+ "calling setContentView() before attempting to show the popup.");
}
if (mBackground != null) {
final ViewGroup.LayoutParams layoutParams = mContentView.getLayoutParams();
int height = ViewGroup.LayoutParams.MATCH_PARENT;
if (layoutParams != null &&
layoutParams.height == ViewGroup.LayoutParams.WRAP_CONTENT) {
height = ViewGroup.LayoutParams.WRAP_CONTENT;
}
// when a background is available, we embed the content view
// within another view that owns the background drawable
PopupViewContainer popupViewContainer = new PopupViewContainer(mContext);
PopupViewContainer.LayoutParams listParams = new PopupViewContainer.LayoutParams(
ViewGroup.LayoutParams.MATCH_PARENT, height
);
popupViewContainer.setBackgroundDrawable(mBackground);
popupViewContainer.addView(mContentView, listParams);
mPopupView = popupViewContainer;
} else {
mPopupView = mContentView;
}
mPopupViewInitialLayoutDirectionInherited =
(mPopupView.getRawLayoutDirection() == View.LAYOUT_DIRECTION_INHERIT);
mPopupWidth = p.width;
mPopupHeight = p.height;
}
可以看到这里在preparePopup方法里，就有了不同，这里如果设置了mBackground就会使用PopupViewContainer保存。
private class PopupViewContainer extends FrameLayout {
1542 private static final String TAG = "PopupWindow.PopupViewContainer";
1543
1544 public PopupViewContainer(Context context) {
1545 super(context);
1546 }
1547
1548 @Override
1549 protected int[] onCreateDrawableState(int extraSpace) {
1550 if (mAboveAnchor) {
1551 // 1 more needed for the above anchor state
1552 final int[] drawableState = super.onCreateDrawableState(extraSpace + 1);
1553 View.mergeDrawableStates(drawableState, ABOVE_ANCHOR_STATE_SET);
1554 return drawableState;
1555 } else {
1556 return super.onCreateDrawableState(extraSpace);
1557 }
1558 }
1559
1560 @Override
1561 public boolean dispatchKeyEvent(KeyEvent event) {
1562 if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
1563 if (getKeyDispatcherState() == null) {
1564 return super.dispatchKeyEvent(event);
1565 }
1566
1567 if (event.getAction() == KeyEvent.ACTION_DOWN
1568 && event.getRepeatCount() == 0) {
1569 KeyEvent.DispatcherState state = getKeyDispatcherState();
1570 if (state != null) {
1571 state.startTracking(event, this);
1572 }
1573 return true;
1574 } else if (event.getAction() == KeyEvent.ACTION_UP) {
1575 KeyEvent.DispatcherState state = getKeyDispatcherState();
1576 if (state != null && state.isTracking(event) && !event.isCanceled()) {
1577 dismiss();
1578 return true;
1579 }
1580 }
1581 return super.dispatchKeyEvent(event);
1582 } else {
1583 return super.dispatchKeyEvent(event);
1584 }
1585 }
1586
1587 @Override
1588 public boolean dispatchTouchEvent(MotionEvent ev) {
1589 if (mTouchInterceptor != null && mTouchInterceptor.onTouch(this, ev)) {
1590 return true;
1591 }
1592 return super.dispatchTouchEvent(ev);
1593 }
1594
1595 @Override
1596 public boolean onTouchEvent(MotionEvent event) {
1597 final int x = (int) event.getX();
1598 final int y = (int) event.getY();
1599
1600 if ((event.getAction() == MotionEvent.ACTION_DOWN)
1601 && ((x < 0) || (x >= getWidth()) || (y < 0) || (y >= getHeight()))) {
1602 dismiss();
1603 return true;
1604 } else if (event.getAction() == MotionEvent.ACTION_OUTSIDE) {
1605 dismiss();
1606 return true;
1607 } else {
1608 return super.onTouchEvent(event);
1609 }
1610 }
1611
1612 @Override
1613 public void sendAccessibilityEvent(int eventType) {
1614 // clinets are interested in the content not the container, make it event source
1615 if (mContentView != null) {
1616 mContentView.sendAccessibilityEvent(eventType);
1617 } else {
1618 super.sendAccessibilityEvent(eventType);
1619 }
1620 }
1621 }
1622
可以看到，这里就直接处理的键盘事件和触摸事件，那么就意味着如果我们没有设置Background那么在低版本的情况下将会出现无法点击外部消失这个功能，虽然后面的修复了这个问题，但是Google也留了一个很大的坑啊，而且为了包装Background在展示上的一致性，在高版本无奈只能选择使用两次包裹来实现，也是费尽心思了。。。
总结
本篇博客主要分析了PopupWindow的实现原理，总的来看，PopupWindow主要是以下几个步骤：
- 设置ContentView
- 利用自定义View包裹我们的ContentView，自定义View重写了键盘事件和触摸事件分发，实现了点击外部消失
- 最终利用WindowManger的addView加入布局，并没有创建新的Window