android代码实现按钮自旋转

代码：

        btn = (Button) findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                final RotateAnimation animation = new RotateAnimation(0.0f, 180.0f,
                        Animation.RELATIVE_TO_SELF, 0.5f,
                        Animation.RELATIVE_TO_SELF, 0.5f);
                animation.setDuration( 500 );
                btn.startAnimation( animation );
            }
        });

布局：