PopUpWindow 位置分析

本段代码实际是计算popupWindow相对母窗口内的偏移值，即p.x,p.y的最终值
 
 private boolean findDropDownPosition(View anchor, WindowManager.LayoutParams p,
            int xoff, int yoff) {
        //状态栏或titile栏的高度
        final int anchorHeight = anchor.getHeight();

        //状态栏或titile栏在窗口中的位置

        anchor.getLocationInWindow(mDrawingLocation); p.x = mDrawingLocation[0] + xoff; p.y = mDrawingLocation[1] + anchorHeight + yoff; boolean onTop = false; p.gravity = Gravity.START | Gravity.TOP;

        //状态栏或titile栏在屏幕中的位置        
        anchor.getLocationOnScreen(mScreenLocation);

        //displayFrame最终窗口的可见大小，对service端的window而言，但在qmw中却是实际的子窗口大小
        final Rect displayFrame = new Rect();
        anchor.getWindowVisibleDisplayFrame(displayFrame);

        //screenY是计算相对屏幕，popUpWindow的y位置
        int screenY = mScreenLocation[1] + anchorHeight + yoff;
        
        //root指decore View，displayFrame.getWidth 和root.getWidth()基本一致
        final View root = anchor.getRootView();
        if (screenY + mPopupHeight > displayFrame.bottom ||
                p.x + mPopupWidth - root.getWidth() > 0) {
            // if the drop down disappears at the bottom of the screen. we try to
            // scroll a parent scrollview or move the drop down back up on top of
            // the edit box
	    //超过窗口高度了，使能scroolview
            if (mAllowScrollingAnchorParent) {
                int scrollX = anchor.getScrollX();
                int scrollY = anchor.getScrollY();
                Rect r = new Rect(scrollX, scrollY,  scrollX + mPopupWidth + xoff,
                        scrollY + mPopupHeight + anchor.getHeight() + yoff);
                anchor.requestRectangleOnScreen(r, true);
            }

            // now we re-evaluate the space available, and decide from that
            // whether the pop-up will go above or below the anchor.
            //重新计算
            anchor.getLocationInWindow(mDrawingLocation);
            p.x = mDrawingLocation[0] + xoff;
            p.y = mDrawingLocation[1] + anchor.getHeight() + yoff;
            
            // determine whether there is more space above or below the anchor
            anchor.getLocationOnScreen(mScreenLocation);
            //判断popupwindow是否上下颠倒？
            onTop = (displayFrame.bottom - mScreenLocation[1] - anchor.getHeight() - yoff) <
                    (mScreenLocation[1] - yoff - displayFrame.top);
            if (onTop) {
                p.gravity = Gravity.START | Gravity.BOTTOM;
                p.y = root.getHeight() - mDrawingLocation[1] + yoff;
            } else {
                p.y = mDrawingLocation[1] + anchor.getHeight() + yoff;
            }
        }

        //mClipToScreen使窗口是clip到screen上而非母窗口(container)
        if (mClipToScreen) {
            final int displayFrameWidth = displayFrame.right - displayFrame.left;

            int right = p.x + p.width;
            if (right > displayFrameWidth) {
                p.x -= right - displayFrameWidth;
            }
           //qmw should change here
           if (p.x < displayFrame.left) {
                p.x = displayFrame.left;
                p.width = Math.min(p.width, displayFrameWidth);
            }

            if (onTop) {
                int popupTop = mScreenLocation[1] + yoff - mPopupHeight;
                if (popupTop < 0) {
                    p.y += popupTop;
                }
            } else {

             //qmw should change here

              p.y = Math.max(p.y, displayFrame.top); } } p.gravity |= Gravity.DISPLAY_CLIP_VERTICAL; return onTop; }