Android自定义View新年烟花、祝福语横幅动画

private static class RollView extends View { 
private Bitmap mBitmap; 
private Rect mSrc; 
private Rect mDst; 
private int mRollWidth = 60; 
private float mRate; 
private boolean mIsStopAnim; 
public RollView(Context context) { 
super(context); 
mSrc = new Rect(); 
mDst = new Rect(); 
} 
@Override 
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
} 
@Override 
protected void onDraw(Canvas canvas) { 
if (mBitmap == null) return; 
drawFromMiddleByFloatCompute(canvas); 
} 
private void drawFromMiddleByFloatCompute(Canvas canvas) { 
/* 
以下src 都需要加上mBitmap. 的前缀，， 因从drawable拿到的是原始图片宽高 
而适配时，可能view的宽高比 drawable的宽高还小或大 
*/ 
final float rate = mRate; 
mSrc.left = 0; 
mSrc.top = 0; 
mSrc.right = mRollWidth; 
mSrc.bottom = mBitmap.getHeight(); 
mDst.left = (int) ((getWidth() / 2 - mRollWidth) - (getWidth() / 2 - mRollWidth) * rate); 
mDst.top = 0; 
mDst.right = mDst.left + mRollWidth + 1;//因精度问题，这里强制+1 
mDst.bottom = getHeight(); 
canvas.drawBitmap(mBitmap, mSrc, mDst, null); 
//中间 
int sw = (int) ((mBitmap.getWidth() - mRollWidth * 2) * rate); 
mSrc.left = mBitmap.getWidth() / 2 - sw / 2; 
mSrc.top = 0; 
mSrc.right = mSrc.left + sw; 
mSrc.bottom = mBitmap.getHeight(); 
int dw = (int) ((getWidth() - mRollWidth * 2) * rate); 
mDst.left = getWidth() / 2 - dw / 2; 
mDst.top = 0; 
mDst.right = mDst.left + dw; 
mDst.bottom = getHeight(); 
canvas.drawBitmap(mBitmap, mSrc, mDst, null); 
//右边 
mSrc.left = mBitmap.getWidth() - mRollWidth; 
mSrc.top = 0; 
mSrc.right = mBitmap.getWidth(); 
mSrc.bottom = mBitmap.getHeight(); 
mDst.left = (int) (getWidth() / 2 + (getWidth() / 2 - mRollWidth) * rate); 
mDst.top = 0; 
mDst.right = mDst.left + mRollWidth; 
mDst.bottom = getHeight(); 
canvas.drawBitmap(mBitmap, mSrc, mDst, null); 
} 
public void setRes(int resId) { 
mBitmap = getBitmapFromLocal(resId); 
} 
@RequiresApi(api = Build.VERSION_CODES.HONEYCOMB) 
public void startFloatComputeAnim() { 
/* 
如果有float获取比率值，从而计算出相应的坐标值，那么可能由于最终在转成Rect的坐标时， 
float to int ，有精度的损失：1个px 而引起效果的不理想 
*/ 
ValueAnimator animator = ValueAnimator.ofFloat(0, 1); 
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { 
@Override 
public void onAnimationUpdate(ValueAnimator animation) { 
if (mIsStopAnim) { 
animation.cancel(); 
return; 
} 
mRate = (float) animation.getAnimatedValue(); 
invalidate(); 
} 
}); 
animator.setDuration(2000); 
animator.start(); 
} 
public void stopAnim() { 
mIsStopAnim = true; 
} 
}