介绍：水波纹散开效果的控件在 App 里面还是比较常见的，例如 网易云音乐歌曲识别，附近搜索场景。

看下实现的效果：

实现思路： 先将最大圆半径与最小圆半径间距分成几等份，从内到外，Paint 透明度依次递减，绘制出同心圆，然后不断的改变这些同心圆的半径大小，延迟一定时间重绘，便达到了想外散开的动画效果了。

public class WaveView extends View { private static final String TAG = "WaveView"; private int waveColor; private int waveCount; private Bitmap waveCenterIcon; private Paint paint; private int mWidth; private int mHeight; private int centerX; private int centerY; private float radius; // 最外圆半径，即最大半径 private float innerRadius; // 最内圆的半径，即最小半径 private int centerIconWidth; private int centerIconHeight; private float[] waveDegreeArr; private boolean isRunning = true; public WaveView(Context context) { this(context, null); } public WaveView(Context context, AttributeSet attrs) { super(context, attrs); readAttrs(context, attrs); init(); } private void init() { paint = new Paint(Paint.ANTI_ALIAS_FLAG); paint.setColor(waveColor); paint.setStyle(Paint.Style.FILL); waveDegreeArr = new float[waveCount]; // 设置中间 drawable 点击事件 } private void readAttrs(Context context, AttributeSet attrs) { TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.WaveView); try { waveColor = typedArray.getColor(R.styleable.WaveView_waveColor, 0xffff0000); waveCount = typedArray.getInt(R.styleable.WaveView_waveCount, 4); Drawable centerDrawable = typedArray.getDrawable(R.styleable.WaveView_waveCenterIcon); waveCenterIcon = ((BitmapDrawable) centerDrawable).getBitmap(); } catch (Exception e) { } finally { typedArray.recycle(); } } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); mWidth = w; mHeight = h; centerX = mWidth / 2; centerY = mHeight / 2; radius = Math.min(mWidth, mHeight) / 2f; centerIconWidth = waveCenterIcon.getWidth(); centerIconHeight = waveCenterIcon.getHeight(); innerRadius = Math.max(centerIconWidth, centerIconHeight) * 1.2f; for (int i = 0; i < waveCount; i++) { waveDegreeArr[i] = innerRadius + (radius - innerRadius) / waveCount * i; } } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { int widthMode = MeasureSpec.getMode(widthMeasureSpec); int heightMode = MeasureSpec.getMode(heightMeasureSpec); if (widthMode == MeasureSpec.UNSPECIFIED || widthMode == MeasureSpec.AT_MOST) { widthMeasureSpec = MeasureSpec.makeMeasureSpec(dp2Px(120), MeasureSpec.EXACTLY); } if (heightMode == MeasureSpec.UNSPECIFIED || heightMode == MeasureSpec.AT_MOST) { heightMeasureSpec = MeasureSpec.makeMeasureSpec(dp2Px(120), MeasureSpec.EXACTLY); } super.onMeasure(widthMeasureSpec, heightMeasureSpec); } @Override protected void onDraw(Canvas canvas) { drawWave(canvas); drawCenterCircle(canvas); drawCenterIcon(canvas); } private void drawCenterCircle(Canvas canvas) { canvas.drawCircle(centerX, centerY, innerRadius, paint); } private void drawWave(Canvas canvas) { for (int i = 0; i < waveCount; i++) { paint.setAlpha((int) (255 - 255 * waveDegreeArr[i] / radius)); canvas.drawCircle(centerX, centerY, waveDegreeArr[i], paint); } for (int i = 0; i < waveDegreeArr.length; i++) { if ((waveDegreeArr[i] += 4) > radius) { waveDegreeArr[i] = innerRadius; } } if (isRunning) { postInvalidateDelayed(50); } } private void drawCenterIcon(Canvas canvas) { paint.setAlpha(255); int left = centerX - centerIconWidth / 2; int top = centerY - centerIconHeight / 2; canvas.drawBitmap(waveCenterIcon, left, top, paint); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_UP: // 处理事件逻辑 handleEvent(event); return true; } return true; } private void handleEvent(MotionEvent event) { float touchX = event.getX(); float touchY = event.getY(); Log.i(TAG, "handleEvent: " + "(" + touchX + "," + touchY + ")"); float distanceX = Math.abs(touchX - centerX); float distanceY = Math.abs(touchY - centerY); // 计算触摸点距离中心点的距离 float distance = (float) Math.sqrt(distanceX * distanceX + distanceY * distanceY); // 当点击的点距离中心点距离小于最内圆半径时，认为是点击有效，否则无效 if (distance < innerRadius) { if (listener != null) { listener.onCenterWaveClick(); } } } OnCenterWaveClickListener listener; public interface OnCenterWaveClickListener { void onCenterWaveClick(); } public void setOnCenterWaveClickListener(OnCenterWaveClickListener listener) { this.listener = listener; } public void toggle() { isRunning = !isRunning; invalidate(); } public boolean isWaveRunning() { return isRunning; } private int dp2Px(int dpValue) { return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dpValue, getResources().getDisplayMetrics()); }}

github地址：https://github.com/xing16/WaveView

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