动态设置ListActivity的背景

private  void onSetBackGround()
{
// 获取当前的layout
mRootView =  ((ViewGroup)findViewById(android.R.id.content)).getChildAt(0);
if (mRootView != null)
{
debugout("mRootView != 0","进来了");
// mRootView 设置背景照片
mRootView.setBackground(getResources().getDrawable(R.drawable.show));
debugout(" mRootView 设置背景照片  ---->>>> ","成功");
}
else
{
debugout(" mRootView 设置背景照片  ---->>>> ","失败，没有获取到View");
}

}