多个SurfaceView层叠显示问题

    当场景中有多个SurfaceView的时候，上层的SurfaceView可能会被下层的遮挡，这个时候需要使用setZOrderOnTop(true)或者setZOrderMediaOverlay(true)来控制SurfaceView的显示层次。

Android SDK对两个函数的描述：

public void setZOrderOnTop (boolean onTop)

Added in  API level 5

Control whether the surface view's surface is placed on top of its window. Normally it is placed behind the window, to allow it to (for the most part) appear to composite with the views in the hierarchy. By setting this, you cause it to be placed above the window. This means that none of the contents of the window this SurfaceView is in will be visible on top of its surface.

Note that this must be set before the surface view's containing window is attached to the window manager.

Calling this overrides any previous call to setZOrderMediaOverlay(boolean).

控制这个surfaceView是否被放在窗口顶层。通常,为了使它与绘图树整合,它被放在窗口之后。通过这个函数，你可以使SurfaceView被放在窗口顶层。这意味着它所在的窗口的其他内容都不可见。（注:可以设置surfaceView透明来使其他内容可见）

这个函数必须在窗口被添加到窗口管理器之前设置。

调用这个函数会使之前调用的setZOrderMediaOverlay(boolean)无效；

public void setZOrderMediaOverlay (boolean isMediaOverlay)

Added in  API level 5

Control whether the surface view's surface is placed on top of another regular surface view in the window (but still behind the window itself). This is typically used to place overlays on top of an underlying media surface view.

Note that this must be set before the surface view's containing window is attached to the window manager.

Calling this overrides any previous call to setZOrderOnTop(boolean).

控制这个surfaceView是否被放在另一个普通的surfaceView上面（但是仍然在窗口之后）。这个函数通常被用来将覆盖层至于一个多媒体层上面。

这个函数必须在窗口被添加到窗口管理器之前设置。

调用这个函数会使之前调用的setZOrderOnTop(boolean)无效。