AnimationDrawable无法启动！

Question

我尝试用这种方式制作动画：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    startAnimation();
}

void startAnimation(){
    AnimationDrawable animDrawable = new AnimationDrawable();
    animDrawable.addFrame(getResources().getDrawable(R.drawable.wait_connextion_0),100);
    animDrawable.addFrame(getResources().getDrawable(R.drawable.wait_connextion_1), 100);
    animDrawable.addFrame(getResources().getDrawable(R.drawable.wait_connextion_2), 100);
    animDrawable.addFrame(getResources().getDrawable(R.drawable.wait_connextion_3), 100);

    animDrawable.setOneShot(false); 
    ImageView waitIV = (ImageView) findViewById(R.id.waitIV);
    waitIV.setBackgroundDrawable(animDrawable); 
    animDrawable.start();
}

但它不起作用，你能告诉我这是什么问题:-(