Android利用动画实现背景逐渐变暗

/** * 动画工具类 * UpdateListener： 动画过程中通过添加此监听来回调数据 * EndListener： 动画结束的时候通过此监听器来做一些处理 */public class AnimUtil {  private ValueAnimator valueAnimator;  private UpdateListener updateListener;  private EndListener endListener;  private long duration;  private float start;  private float end;  private Interpolator interpolator = new LinearInterpolator();  public AnimUtil() {    duration = 1000; //默认动画时常1s    start = 0.0f;    end = 1.0f;    interpolator = new LinearInterpolator();// 匀速的插值器  }  public void setDuration(int timeLength) {    duration = timeLength;  }  public void setValueAnimator(float start, float end, long duration) {    this.start = start;    this.end = end;    this.duration = duration;  }  public void setInterpolator(Interpolator interpolator) {    this.interpolator = interpolator;  }  public void startAnimator() {    if (valueAnimator != null){      valueAnimator = null;    }    valueAnimator = ValueAnimator.ofFloat(start, end);    valueAnimator.setDuration(duration);    valueAnimator.setInterpolator(interpolator);    valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {      @Override      public void onAnimationUpdate(ValueAnimator valueAnimator) {        if (updateListener == null) {          return;        }        float cur = (float) valueAnimator.getAnimatedValue();        updateListener.progress(cur);      }    });    valueAnimator.addListener(new Animator.AnimatorListener() {      @Override      public void onAnimationStart(Animator animator) {}      @Override      public void onAnimationEnd(Animator animator) {        if(endListener == null){          return;        }        endListener.endUpdate(animator);      }      @Override      public void onAnimationCancel(Animator animator) {}      @Override      public void onAnimationRepeat(Animator animator) {}    });    valueAnimator.start();  }  public void addUpdateListener(UpdateListener updateListener) {    this.updateListener = updateListener;  }  public void addEndListner(EndListener endListener){    this.endListener = endListener;  }  public interface EndListener {    void endUpdate(Animator animator);  }  public interface UpdateListener {    void progress(float progress);  }}

public class MainActivity extends AppCompatActivity {  private AnimUtil animUtil;  private float bgAlpha = 1f;  private boolean bright = false;  PopupWindow popupWindow;  Button button;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    animUtil = new AnimUtil();    button = (Button) findViewById(R.id.btn);    button.setOnClickListener(new View.OnClickListener() {      @Override      public void onClick(View view) {        bottomwindow(button);        toggleBright();      }    });  }  private void toggleBright() {    //三个参数分别为： 起始值 结束值 时长 那么整个动画回调过来的值就是从0.5f--1f的    animUtil.setValueAnimator(0.5f, 1f, 350);    animUtil.addUpdateListener(new AnimUtil.UpdateListener() {      @Override      public void progress(float progress) {        //此处系统会根据上述三个值，计算每次回调的值是多少，我们根据这个值来改变透明度        bgAlpha = bright ? progress : (1.5f - progress);//三目运算，应该挺好懂的。        backgroundAlpha(bgAlpha);//在此处改变背景，这样就不用通过Handler去刷新了。      }    });    animUtil.addEndListner(new AnimUtil.EndListener() {      @Override      public void endUpdate(Animator animator) {        //在一次动画结束的时候，翻转状态        bright = !bright;      }    });    animUtil.startAnimator();  }  /***   * 此方法用于改变背景的透明度，从而达到“变暗”的效果   */  private void backgroundAlpha(float bgAlpha) {    WindowManager.LayoutParams lp = getWindow().getAttributes();    lp.alpha = bgAlpha; //0.0-1.0    getWindow().setAttributes(lp);    getWindow().addFlags(WindowManager.LayoutParams.FLAG_DIM_BEHIND);  }  void bottomwindow(View view) {    if (popupWindow != null && popupWindow.isShowing()) {      return;    }    LinearLayout layout = (LinearLayout) getLayoutInflater().inflate(R.layout.window_popup, null);    popupWindow = new PopupWindow(layout,        ViewGroup.LayoutParams.MATCH_PARENT,        ViewGroup.LayoutParams.WRAP_CONTENT);    //点击空白处时，隐藏掉pop窗口    popupWindow.setFocusable(true);    popupWindow.setBackgroundDrawable(new BitmapDrawable());    popupWindow.setAnimationStyle(R.style.Popupwindow);    int[] location = new int[2];    view.getLocationOnScreen(location);    popupWindow.showAtLocation(view, Gravity.LEFT | Gravity.BOTTOM, 0, -location[1]);    popupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {      @Override      public void onDismiss() {        toggleBright();      }    });  }}