Android-利用动画实现背景逐渐变暗

Posted 2022-11-06 Arbo_Xjb

前言

之前写了一篇Android-实现底部弹出PopupWindow并让背景逐渐变暗，介绍利用Handler动态改变背景透明度从而达到变暗的效果。现在补充一种方法，使用动画来实现相同的效果。

ValueAnimator 和 Interpolator

今天的主角就是这俩，关于ValueAnimator和Interpolator（插值器）的概念请各位自行补充，这里主要讲述怎么用到我们这里来（因为我也不很懂(捂脸)）。

效果

跟之前没有太大区别，只是为了演示变暗、变亮的过程 ↓

代码

• AnimUtil.java

/**
 * 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);
    

• MainActivity.java

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();
            
        );
    

代码很简单，注释都写了。

小结：

对比之前的那种用Handler的方法写的，这种感觉代码更简洁，更容易在多处使用，也算是填坑吧，哈哈。 如果本文埋下了另一个坑，请大家指正，谢谢！

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