Android实现水波纹效果

最近需要做个类似于水波纹动画的效果，思考了一下不需要UI切个动态图，Android原生的技术利用动画或者自定义控件都可以实现。下面上个图类似于这样的效果

下面请看第一种动画实现，这种方式较为简单些，就是利用3个ImageView不断地做缩放和渐变的动画。

布局文件定义一下

接下来中间的ImageView保持不变，通过操作另外两个ImageView达到效果

private void setAnim1() {
    AnimationSet as = new AnimationSet(true);
    //缩放动画，以中心从原始放大到1.4倍
    ScaleAnimation scaleAnimation = new ScaleAnimation(1.0f, 1.4f, 1.0f, 1.4f,
            ScaleAnimation.RELATIVE_TO_SELF, 0.5f,
            ScaleAnimation.RELATIVE_TO_SELF, 0.5f);
    //渐变动画
    AlphaAnimation alphaAnimation = new AlphaAnimation(1.0f, 0.5f);
    scaleAnimation.setDuration(800);
    scaleAnimation.setRepeatCount(Animation.INFINITE);
    alphaAnimation.setRepeatCount(Animation.INFINITE);
    as.setDuration(800);
    as.addAnimation(scaleAnimation);
    as.addAnimation(alphaAnimation);
    iv1.startAnimation(as);
}
private void setAnim2() {
    AnimationSet as = new AnimationSet(true);
    //缩放动画，以中心从1.4倍放大到1.8倍
    ScaleAnimation scaleAnimation = new ScaleAnimation(1.4f, 1.8f, 1.4f, 1.8f,
            ScaleAnimation.RELATIVE_TO_SELF, 0.5f,
            ScaleAnimation.RELATIVE_TO_SELF, 0.5f);
    //渐变动画
    AlphaAnimation alphaAnimation = new AlphaAnimation(0.5f, 0.1f);
    scaleAnimation.setDuration(800);
    scaleAnimation.setRepeatCount(Animation.INFINITE);
    alphaAnimation.setRepeatCount(Animation.INFINITE);
    as.setDuration(800);
    as.addAnimation(scaleAnimation);
    as.addAnimation(alphaAnimation);
    iv2.startAnimation(as);
}

接下来就是第二种自定义动画实现
首先定义style文件自定义属性--在values下创建attrs.xml文件

接下来创建SpreadView继承view,初始化构造方法

public SpreadView(Context context) {
    this(context,null,0);
}

public SpreadView(Context context, @Nullable AttributeSet attrs) {
    this(context, attrs,0);
}

public SpreadView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.SpreadView, defStyleAttr, 0);
    radius = a.getInt(R.styleable.SpreadView_spread_radius, radius);
    maxRadius = a.getInt(R.styleable.SpreadView_spread_max_radius, maxRadius);
    int centerColor = a.getColor(R.styleable.SpreadView_spread_center_color, ContextCompat.getColor(context, R.color.colorAccent));
    int spreadColor = a.getColor(R.styleable.SpreadView_spread_spread_color, ContextCompat.getColor(context, R.color.colorAccent));
    distance = a.getInt(R.styleable.SpreadView_spread_distance, distance);
    a.recycle();
    centerPaint = new Paint();
    centerPaint.setColor(centerColor);
    centerPaint.setAntiAlias(true);
    //最开始不透明且扩散距离为0
    alphas.add(255);
    spreadRadius.add(0);
    spreadPaint = new Paint();
    spreadPaint.setAntiAlias(true);
    spreadPaint.setAlpha(255);
    spreadPaint.setColor(spreadColor);
}

自定义View的绘制：

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    for (int i = 0; i < spreadRadius.size(); i++) {
        int alpha = alphas.get(i);
        spreadPaint.setAlpha(alpha);
        int width = spreadRadius.get(i);
        //绘制扩散的圆
        canvas.drawCircle(centerX, centerY, radius + width, spreadPaint);
        //每次扩散圆半径递增，圆透明度递减
        if (alpha > 0 && width < 300) {
            alpha = alpha - distance > 0 ? alpha - distance : 1;
            alphas.set(i, alpha);
            spreadRadius.set(i, width + distance);
        }
    }
    //当最外层扩散圆半径达到最大半径时添加新扩散圆
    if (spreadRadius.get(spreadRadius.size() - 1) > maxRadius) {
        spreadRadius.add(0);
        alphas.add(255);
    }
    //超过8个扩散圆，删除最先绘制的圆，即最外层的圆
    if (spreadRadius.size() >= 8) {
        alphas.remove(0);
        spreadRadius.remove(0);
    }
    //中间的圆
    canvas.drawCircle(centerX, centerY, radius, centerPaint);
    //延迟更新，达到扩散视觉差效果
    postInvalidateDelayed(delayMilliseconds);
}

最后在activity的布局文件中引用自定义属性：

以上两种方法就实现了水波纹的效果，下载完整的demo请点击链接，希望对大家有所帮助https://download.csdn.net/download/lou_liang/10750534