Android双指缩放ScaleGestureDetector检测放大因子大图移动到双指中心点ImageView区域中心，Kotlin（2）
在 Android ScaleGestureDetector检测双指缩放Bitmap基于Matrix动画移动到双指捏合中心点ImageView区域中心，Kotlin-CSDN博客 的基础上，改进一下，实现两根手指在屏幕上捏合缩放时候，图片随之缩放。当手指在屏幕上抬离时候，画布上呈现的是缩放后的图。
class MyImageView : AppCompatImageView {private var mCenterX = 0fprivate var mCenterY = 0fprivate val mCirclePaint = Paint()private var mSrcBmp: Bitmap? = nullprivate var mScaleBmp: Bitmap? = null//放大系数。private var mScaleFactor = 1fprivate var mScaleGestureDetector: ScaleGestureDetector? = nullprivate var mCanDrawScaleBmp = falseconstructor(ctx: Context, attrs: AttributeSet) : super(ctx, attrs) {mSrcBmp = (drawable as BitmapDrawable).bitmap //mSrcBmp是原始图大小，没有缩放和拉伸的。mCirclePaint.style = Paint.Style.STROKEmCirclePaint.strokeWidth = 10fmCirclePaint.isAntiAlias = truemCirclePaint.color = Color.REDmScaleGestureDetector = ScaleGestureDetector(ctx, object : ScaleGestureDetector.SimpleOnScaleGestureListener() {override fun onScale(detector: ScaleGestureDetector): Boolean {//更新两个手指缩放的中心点。mCenterX = detector.focusXmCenterY = detector.focusY//if (detector.currentSpan > 50 && detector.timeDelta > 20) {mScaleFactor = detector.scaleFactorLog.d("fly", "onScaleEnd scaleFactor=${detector.scaleFactor}")//}updateView()return false}})}private fun updateView() {this.invalidate()}override fun onTouchEvent(event: MotionEvent): Boolean {mScaleGestureDetector?.onTouchEvent(event)when (event.actionMasked) {MotionEvent.ACTION_MOVE -> {mCanDrawScaleBmp = true}MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {//如果抬手时候重新置false，没有绘制，显示原始底图。//mCanDrawScaleBmp = false}}return true}override fun onDraw(canvas: Canvas) {super.onDraw(canvas)if (mCanDrawScaleBmp) {myDraw(canvas)}}private fun myDraw(canvas: Canvas) {mScaleBmp = Bitmap.createScaledBitmap(mSrcBmp!!,(this.width * mScaleFactor + 1).toInt(), //注意这里的精度损失，会造成坐标偏移.(this.height * mScaleFactor + 1).toInt(),//注意这里的精度损失，会造成坐标偏移.true)val cx = this.width / 2fval cy = this.height / 2fval matrix = Matrix()matrix.setScale(mScaleFactor, mScaleFactor)matrix.setTranslate(cx - mCenterX * mScaleFactor, cy - mCenterY * mScaleFactor)canvas.drawBitmap(mScaleBmp!!, matrix, null)//中心圆圈canvas.drawCircle(cx, cy, 50f, mCirclePaint)}
}
需要改进的地方是滑动缩放过程不是图片缩放不是非常丝滑流畅，需要改善。
Android ScaleGestureDetector检测双指缩放Bitmap基于Matrix动画移动到双指捏合中心点ImageView区域中心，Kotlin-CSDN博客文章浏览阅读75次，点赞3次，收藏5次。需要注意的，因为在xml布局里面特别设置了ImageView的高度为wrap_content，手指在屏幕触点的位置是放大镜里面放大图片后准确圆心位置，但是，如果ImageView设置成match_parent，则因为ImageView里面的Bitmap被缩放(此处Bitmap其实小于ImageView，被拉伸了)，拉伸后的Bitmap水平方向坐标与ImageView一直重合，但竖直方向，Bitmap坐标与ImageView不一致，会造成一种现象，手指触点放大镜放大后，水平方向是正确的，但竖直方向有偏移量。https://blog.csdn.net/zhangphil/article/details/135705931
