android studio 按钮渐变动画

Android Studio 的渐变按钮及其简单，一共三行代码

看以下红色的三行

public class MainActivity extends AppCompatActivity {
ImageButton imageButton_start_game;
TextView textView_kuaicai;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//开始游戏按钮事件
imageButton_start_game=(ImageButton) findViewById(R.id.imageButton_start_game);
imageButton_start_game.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Animation animation=new AlphaAnimation(1.0f,0.0f);
animation.setDuration(300);
imageButton_start_game.startAnimation(animation);
Intent intent_sart_game=new Intent("com.nnmoo.www.words_puzzle_android.GameActivity");
// startActivity(intent_sart_game);
}
});
}

}