Android开发Splash界面亮度的渐变效果

public class WelcomeActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.welcome);
        
        
        //1.拿到当前acitivity的layout的view
        View view  = findViewById(R.id.welcome_layout);
        
        //2.绑定透明度变化的动画
        AlphaAnimation anim = new AlphaAnimation(0.1f, 1.0f);
        anim.setDuration(3000);
        view.startAnimation(anim);
        
        //3.动画执行完毕后，进入主页面
        anim.setAnimationListener(am);

    }
    
    private AnimationListener am = new AnimationListener() {
    	@Override
		public void onAnimationEnd(Animation animation) {
    		//动画执行结束的时候去主页面
    		Intent intent = new Intent();
    		intent.setClass(WelcomeActivity.this, PageActivity.class);
    		startActivity(intent);
    		finish();
		}
		@Override
		public void onAnimationStart(Animation animation) {
		}
		
		@Override
		public void onAnimationRepeat(Animation animation) {
		}
	};

	@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		//监听的back键按下的时候什么也不处理
		//直接在当前页面忽略任何按键
//		if (keyCode == KeyEvent.KEYCODE_BACK) {
//			//监听到返回键，
//		}
		return false;
	}
}
public class WelcomeActivity extends Activi