最近项目中遇到指纹支付的需求，有个扫指纹的动画需求

效果图

实现原理

需要重写View,在onDraw方法中完成绘制,使用canvas的drawBitmap方法：

drawBitmap(Bitmap bitmap, Rect src, RectF dst, Paint paint)；

第一个Rect 代表要绘制的bitmap 区域，第二个 Rect 代表的是要将bitmap 绘制在屏幕的什么地方

首先，在构造函数中，初始化bitmap，paint：

mFingerGreen= ((BitmapDrawable) ContextCompat.getDrawable(mContext,R.drawable.finger_green)).getBitmap();

mFingerGrey= ((BitmapDrawable) ContextCompat.getDrawable(mContext,R.drawable.finger_grey)).getBitmap();

mLine= ((BitmapDrawable) ContextCompat.getDrawable(mContext,R.drawable.finger_line)).getBitmap();

mBitWidth=mFingerGreen.getWidth();

mBitHeight=mFingerGreen.getHeight();

mBitPaint=newPaint();

// 防抖动

mBitPaint.setDither(true);

// 开启图像过滤

mBitPaint.setFilterBitmap(true);

mSrcRect=newRect();

mDestRect=newRect();

在onDraw(Canvas canvas)方法绘制图片

@Override

protected voidonDraw(Canvas canvas) {

super.onDraw(canvas);

//显示在view中间

inthalfViewWidth =mWidth/2;

inthalfViewHeight =mHeight/2;

intleft =0;

inttop =0;

mBitPaint.setAlpha(255);

mSrcRect.set(left,top,mBitWidth,mBitHeight);

left = halfViewWidth -mFingerGrey.getWidth() /2;

top = halfViewHeight -mFingerGrey.getHeight() /2;

mDestRect.set(left,top,mBitWidth+ left,mBitHeight+ top);

canvas.drawBitmap(mFingerGrey,mSrcRect,mDestRect,mBitPaint);//画灰色底图

left =0;

top =0;

mSrcRect.set(left,top,mBitWidth,(int) (mBitHeight*mFraction));

left = halfViewWidth -mFingerGreen.getWidth() /2;

top = halfViewHeight -mFingerGreen.getHeight() /2;

mDestRect.set(left,top,mBitWidth+ left,(int) (mBitHeight*mFraction) + top);

canvas.drawBitmap(mFingerGreen,mSrcRect,mDestRect,mBitPaint);//画绿色图片

left = halfViewWidth -mLine.getWidth() /2;

canvas.drawBitmap(mLine,left,mDestRect.bottom,mBitPaint);//画线

}

最后，利用ValueAnimator，修改mFraction的值，得到每次移动的步长，invalidate()重新绘画。

public voidstartScaning() {

ValueAnimator valueAnimator = ValueAnimator.ofFloat(0.f,100.f);

valueAnimator.setDuration(1000);

valueAnimator.setInterpolator(newLinearInterpolator());

valueAnimator.addUpdateListener(newValueAnimator.AnimatorUpdateListener() {

@SuppressLint("NewApi")

@Override

public voidonAnimationUpdate(ValueAnimator valueAnimator) {

mFraction= valueAnimator.getAnimatedFraction();

invalidate();

}

});

valueAnimator.addListener(newAnimator.AnimatorListener() {

@Override

public voidonAnimationStart(Animator animator) {

}

@Override

public voidonAnimationEnd(Animator animator) {

mFraction=0;

if(isAnim) {

startScaning();

}

}

@Override

public voidonAnimationCancel(Animator animator) {

}

@Override

public voidonAnimationRepeat(Animator animator) {

}

});

if(!valueAnimator.isRunning()) {

valueAnimator.start();

}

}

大功告成，最后附上需要的四张图片：