SlidingDrawer动画不可见

Question

我对SlidingDrawer动画有一些问题。 我有View

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"

    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <RelativeLayout 
        android:id="@+id/rlGL"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

    </RelativeLayout>


    <SlidingDrawer
        android:id="@+id/slidingDrawer1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:topOffset="900dp"
        android:content="@+id/content"
        android:handle="@+id/handle"
        android:orientation="horizontal" 
        android:animateLayoutChanges="false">

        <ImageView
            android:id="@+id/handle"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:src="@drawable/add" />

        <LinearLayout
            android:id="@+id/content"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:measureWithLargestChild="true"
            android:orientation="vertical" 
            android:background="#171717">

        <Button
            android:id="@+id/bOk"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/ok"  
            android:textSize="48sp">

        </Button>

    </LinearLayout>
    </SlidingDrawer>

</FrameLayout>

这个“空”RelativeLayout我用于SurfaceView（用于相机预览）和GLSurfaceView（用于具有透明背景的OpenGL场景）。有一个代码：

MainActivity.java

...
setContentView(R.layout.activity_main);

relLayout = (RelativeLayout) findViewById(R.id.rlGL);


mGLSurfaceView = new MyGlSurfaceView(this); 
mGLSurfaceView.getHolder().setFormat(PixelFormat.TRANSLUCENT);
relLayout.addView(mGLSurfaceView, new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT));

preview = new SurfaceView(this);        
surfaceHolder = preview.getHolder();
surfaceHolder.addCallback(this);
relLayout.addView(preview, new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT));
...

问题是，点击抽屉的手柄图像后，它会消失片刻（动画运行时），然后出现在打开状态。为什么会这样？