这里我们以解决 PopupWindow 显示的一个问题作为目标来进行分析。
问题描述
想要的效果
在控件上方显示，可能是单行，也可能是多行。
实现方式
使用 showAsDropdown 时，可通过 yOffset 参数指定Y轴方向上的偏移量：
偏移量 = anchorView.height + popupWindow.height
对于第 2 种单行的弹出框来说，实现起来比较简单:
class RawPopupWindowActivity : DemoButtonsActivity() {
private var popupWindow: PopupWindow? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
addButton("单行Popup") { v -> showPopup(v, Constants.TEXT_SHORT) }
addButton("多行Popup") { v -> showPopup(v, Constants.TEXT_MEDIUM) }
addButton("多行Popup") { v -> showPopup(v, Constants.TEXT_LONG) }
}
private fun showPopup(anchorView: View, content: String) {
popupWindow?.run {
dismiss()
}
popupWindow = PopupWindow(applicationContext).apply {
isOutsideTouchable = true
PopupHelper(applicationContext).run {
contentView = binding.root
setText(content)
}
width = WindowManager.LayoutParams.WRAP_CONTENT
height = WindowManager.LayoutParams.WRAP_CONTENT
setBackgroundDrawable(ColorDrawable(Color.TRANSPARENT))
// 测量高度
contentView.measure(
View.MeasureSpec.makeMeasureSpec(width, View.MeasureSpec.UNSPECIFIED),
View.MeasureSpec.makeMeasureSpec(height, View.MeasureSpec.UNSPECIFIED)
)
// 显示时向上移动 anchorView.height + contentView.measuredHeight
showAsDropDown(anchorView, 0, -(anchorView.height + contentView.measuredHeight))
}
}
}
实现效果及问题
最终效果如下：
可以看到垂直方向上：
- 单行的没有偏移
- 两行的有些许偏移
- 多行的偏移就非常大了
这是因为我们测量的时候并不是按照PopupWindow本身的测量方式进行测量的，所以height的值不匹配真实高度。
Window添加过程
showAsDropDown
// android/widget/PopupWindow.java
public void showAsDropDown(View anchor, int xoff, int yoff) {
showAsDropDown(anchor, xoff, yoff, DEFAULT_ANCHORED_GRAVITY);
}
public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {
if (isShowing() || !hasContentView()) {
return;
}
// 关闭 mDecorView 上的动画
TransitionManager.endTransitions(mDecorView);
// 建下方
attachToAnchor(anchor, xoff, yoff, gravity);
mIsShowing = true;
mIsDropdown = true;
// 根据传递进来的参数，设置布局参数
final WindowManager.LayoutParams p =
createPopupLayoutParams(anchor.getApplicationWindowToken());
// 创建 DecorView BackgroundView ContentView 几个层次的包装
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;
invokePopup(p);
}
attachToAnchor
protected void attachToAnchor(View anchor, int xoff, int yoff, int gravity) {
detachFromAnchor();
final ViewTreeObserver vto = anchor.getViewTreeObserver();
if (vto != null) {
vto.addOnScrollChangedListener(mOnScrollChangedListener);
}
// View被添加到Window或者从Window上分离时的监听
anchor.addOnAttachStateChangeListener(mOnAnchorDetachedListener);
final View anchorRoot = anchor.getRootView();
anchorRoot.addOnAttachStateChangeListener(mOnAnchorRootDetachedListener);
// 因为布局变化导致View的边界变化时的监听
anchorRoot.addOnLayoutChangeListener(mOnLayoutChangeListener);
// 存储 锚View 的一些信息
mAnchor = new WeakReference<>(anchor);
mAnchorRoot = new WeakReference<>(anchorRoot);
mIsAnchorRootAttached = anchorRoot.isAttachedToWindow();
mParentRootView = mAnchorRoot;
mAnchorXoff = xoff;
mAnchorYoff = yoff;
mAnchoredGravity = gravity;
}
从这里得到如下信息：
mAnchor： 锚View （弱引用）mAnchorRoot： 锚View的顶层View (弱引用)mParentRootView： mAnchorRoot （强引用）
createPopupLayoutParams
就是 LayoutParams 设置
protected final WindowManager.LayoutParams createPopupLayoutParams(IBinder token) {
final WindowManager.LayoutParams p = new WindowManager.LayoutParams();
p.gravity = computeGravity();
p.flags = computeFlags(p.flags);
p.type = mWindowLayoutType;
p.token = token;
p.softInputMode = mSoftInputMode;
p.windowAnimations = computeAnimationResource();
// 设置了背景时，从背景Drawable取像素格式
if (mBackground != null) {
p.format = mBackground.getOpacity();
} else {
p.format = PixelFormat.TRANSLUCENT;
}
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;
}
preparePopup
private void preparePopup(WindowManager.LayoutParams p) {
// When a background is available, we embed the content view within
// another view that owns the background drawable.
if (mBackground != null) {
mBackgroundView = createBackgroundView(mContentView);
mBackgroundView.setBackground(mBackground);
} else {
mBackgroundView = mContentView;
}
mDecorView = createDecorView(mBackgroundView);
}
总体就是为了创建如下层次的 View：
不过， DecorView 上有附加效果，主要是事件和动画相关的。后面具体进行分析。
findDropDownPosition
就像其注释说的，计算PopupWindow 在屏幕上面的位置：
- 如果PopupWindow太高，无法放置到anchor的下方，则会检测上层是否有可滚动的视图，并向上滚动以获取可用空间。
- 如果父布局无法滚动，popupWindow会放置到anchor的上方。
protected boolean findDropDownPosition(View anchor, WindowManager.LayoutParams outParams,
int xOffset, int yOffset, int width, int height, int gravity, boolean allowScroll) {
// 获取 anchor宽高
final int anchorHeight = anchor.getHeight();
final int anchorWidth = anchor.getWidth();
// 允许重叠时，会先上移动 anchor 的高度
if (mOverlapAnchor) {
yOffset -= anchorHeight;
}
// 先尝试将位置放置在anchor的左下角并加上偏移量
// 获取anchor的rootView在屏幕上的位置 appScreenLocation
final int[] appScreenLocation = mTmpAppLocation;
final View appRootView = getAppRootView(anchor);
appRootView.getLocationOnScreen(appScreenLocation);
// 获取 anchor 在屏幕上的位置 screenLocation
final int[] screenLocation = mTmpScreenLocation;
anchor.getLocationOnScreen(screenLocation);
// 计算初步的绘制位置
final int[] drawingLocation = mTmpDrawingLocation;
drawingLocation[0] = screenLocation[0] - appScreenLocation[0];
drawingLocation[1] = screenLocation[1] - appScreenLocation[1];
outParams.x = drawingLocation[0] + xOffset;
outParams.y = drawingLocation[1] + anchorHeight + yOffset;
// 如果宽高参数为 MATCH_PARENT 时，根据外层可用空间计算真正的具体宽高数值
final Rect displayFrame = new Rect();
appRootView.getWindowVisibleDisplayFrame(displayFrame);
if (width == MATCH_PARENT) {
width = displayFrame.right - displayFrame.left;
}
if (height == MATCH_PARENT) {
height = displayFrame.bottom - displayFrame.top;
}
// Let the window manager know to align the top to y.
outParams.gravity = computeGravity();
outParams.width = width;
outParams.height = height;
// 第一阶段完成
// 第二阶段：尝试（在不调整大小的情况下）调整Popup的垂直方向，通过返回值可以判断垂直方向上是否够用
final boolean fitsVertical = tryFitVertical(outParams, yOffset, height,
anchorHeight, drawingLocation[1], screenLocation[1], displayFrame.top,
displayFrame.bottom, false);
// 第三阶段：接下来,尝试（在不调整大小的情况下）调整Popup的水平方向，通过返回值可以判断水平方向上是否够用
final boolean fitsHorizontal = tryFitHorizontal(outParams, xOffset, width,
anchorWidth, drawingLocation[0], screenLocation[0], displayFrame.left,
displayFrame.right, false);
// 第四阶段：如果无法满足Popup的显示，则尝试滚动父View
if (!fitsVertical || !fitsHorizontal) {
final int scrollX = anchor.getScrollX();
final int scrollY = anchor.getScrollY();
final Rect r = new Rect(scrollX, scrollY, scrollX + width + xOffset,
scrollY + height + anchorHeight + yOffset);
if (allowScroll && anchor.requestRectangleOnScreen(r, true)) {
// Reset for the new anchor position.
anchor.getLocationOnScreen(screenLocation);
drawingLocation[0] = screenLocation[0] - appScreenLocation[0];
drawingLocation[1] = screenLocation[1] - appScreenLocation[1];
outParams.x = drawingLocation[0] + xOffset;
outParams.y = drawingLocation[1] + anchorHeight + yOffset;
// Preserve the gravity adjustment.
if (hgrav == Gravity.RIGHT) {
outParams.x -= width - anchorWidth;
}
}
// Try to fit the popup again and allowing resizing.
tryFitVertical(outParams, yOffset, height, anchorHeight, drawingLocation[1],
screenLocation[1], displayFrame.top, displayFrame.bottom, mClipToScreen);
tryFitHorizontal(outParams, xOffset, width, anchorWidth, drawingLocation[0],
screenLocation[0], displayFrame.left, displayFrame.right, mClipToScreen);
}
// Return whether the popup's top edge is above the anchor's top edge.
return outParams.y < drawingLocation[1];
}
第一阶段的计算过程如下，得到最后的x，y值：
tryFitVertical
private boolean tryFitVertical(@NonNull LayoutParams outParams, int yOffset, int height,
int anchorHeight, int drawingLocationY, int screenLocationY, int displayFrameTop,
int displayFrameBottom, boolean allowResize) {
// 计算Y方向上的 offset，screenLocationY为anchorView的Y，drawingLocationY为popup的Y
final int winOffsetY = screenLocationY - drawingLocationY;
// anchor
final int anchorTopInScreen = outParams.y + winOffsetY;
final int spaceBelow = displayFrameBottom - anchorTopInScreen;
if (anchorTopInScreen >= displayFrameTop && height <= spaceBelow) {
return true;
}
final int spaceAbove = anchorTopInScreen - anchorHeight - displayFrameTop;
if (height <= spaceAbove) {
// Move everything up.
if (mOverlapAnchor) {
yOffset += anchorHeight;
}
outParams.y = drawingLocationY - height + yOffset;
return true;
}
if (positionInDisplayVertical(outParams, height, drawingLocationY, screenLocationY,
displayFrameTop, displayFrameBottom, allowResize)) {
return true;
}
return false;
}