PopupWindow 高度是match_parent的时候，铺满全屏的问题

问题

在以前，我们一直使用showAsDropDown 来让PopupWindow 显示在某个anchor的下边，哪怕这个PopupWindow高度是match_parent的，可24以后，你会发现，它不再是显示在anchor下边，而是铺满整个屏幕的，把anchor都盖住了.

简单的使用

        val popup=PopupWindow(WindowManager.LayoutParams.MATCH_PARENT,WindowManager.LayoutParams.MATCH_PARENT).apply {
            contentView=LayoutInflater.from(baseContext).inflate(R.layout.popup_test,null)
            this.isTouchable=true
            this.isFocusable=true;

        }

popup.showAsDropDown(tg)

我们分析下7.0和6.0的源码有啥区别

6.0的源码

    public void showAtLocation(IBinder token, int gravity, int x, int y) {
        if (isShowing() || mContentView == null) {
            return;
        }

        TransitionManager.endTransitions(mDecorView);

        unregisterForScrollChanged();

        mIsShowing = true;
        mIsDropdown = false;

        final LayoutParams p = createPopupLayoutParams(token);
        preparePopup(p);

        // Only override the default if some gravity was specified.
        if (gravity != Gravity.NO_GRAVITY) {
            p.gravity = gravity;
        }

        p.x = x;
        p.y = y;

        invokePopup(p);
    }

7.0的源码

    public void showAsDropDown(View anchor, int xoff, int yoff, int gravity) {
        if (isShowing() || !hasContentView()) {
            return;
        }

        TransitionManager.endTransitions(mDecorView);

        attachToAnchor(anchor, xoff, yoff, gravity);

        mIsShowing = true;
        mIsDropdown = true;

        final WindowManager.LayoutParams p =
                createPopupLayoutParams(anchor.getApplicationWindowToken());
        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);
    }

可以看到7.0的多了两行代码，看名字aboveAnchor，它会判断是否显示在anchor上

        final boolean aboveAnchor = findDropDownPosition(anchor, p, xoff, yoff,
                p.width, p.height, gravity, mAllowScrollingAnchorParent);
        updateAboveAnchor(aboveAnchor);

在分析这两行代码之前，先看下默认生成个的params里的高度是啥
进入createPopupLayoutParams方法
mHeightMode :默认是0，如果你没设置的话，我们一般都没设置这个，所以会走else
而mHeight，我们在构造方法里设置的是match_parent也就是-1

protected final WindowManager.LayoutParams createPopupLayoutParams(IBinder token) {

        if (mHeightMode < 0) {
            p.height = mLastHeight = mHeightMode;
        } else {
            p.height = mLastHeight = mHeight;
        }
}

然后继续看findDropDownPosition

 protected boolean findDropDownPosition(View anchor, WindowManager.LayoutParams outParams,
            int xOffset, int yOffset, int width, int height, int gravity, boolean allowScroll) {
//...
final Rect displayFrame = new Rect();
        appRootView.getWindowVisibleDisplayFrame(displayFrame);
//...可以看到，高度就是整个容器的高度，差不多就是屏幕的高度了
        if (height == MATCH_PARENT) {
            height = displayFrame.bottom - displayFrame.top;
        }

//...下边会判断我们这个高度是否会超出屏幕，如果超出屏幕的话，会返回false
        // First, attempt to fit the popup vertically without resizing.
        final boolean fitsVertical = tryFitVertical(outParams, yOffset, height,
                anchorHeight, drawingLocation[1], screenLocation[1], displayFrame.top,
                displayFrame.bottom, false);
}
//...下边会处理false的情况的，会都params的y进行处理的，处理结果就是，y的位置不再是anchor下边了，因为 Popup高度是屏幕高度了，所以y差不多就是0了.具体就不分析了
 // If the popup still doesn't fit, attempt to scroll the parent.
        if (!fitsVertical || !fitsHorizontal) {

}

总结

看完源码就发现了，24以上，match_parent的话，Popup的高度就是全屏高度了，所以，如果还想显示在anchor下边，那就只能用wrap_content,或者 自己计算下anchor底部到屏幕底部的距离，也就是Popup需要展示的高度，自己手动setHeight

计算anchor或者容器的位置大小也很简单，下边这种就行

final Rect displayFrame = new Rect();
        appRootView.getWindowVisibleDisplayFrame(displayFrame);