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
在 Android双击图片放大移动图中双击点到ImageView区域中心，Kotlin-CSDN博客 基础上，这次使用ScaleGestureDetector检测两根手指的缩放动作，记录两根手指的中心点位置，根据ScaleGestureDetector检测到的缩放因子（系数），放大原图，并移动放大前两根手指中心点在原图的位置移动到放大后区域。
class MyImageView : AppCompatImageView {private var mCenterX = 0fprivate var mCenterY = 0fprivate val mCirclePaint = Paint()private var mSrcBmp: Bitmap? = nullprivate var mScaleBmp: Bitmap? = nullprivate var testIV: ImageView? = null//放大系数。private var mScaleFactor = 1fprivate var mScaleGestureDetector: ScaleGestureDetector? = nullprivate var mCanDrawScaleBmp = falseprivate var mCanDrawCircle = 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 onScaleEnd(detector: ScaleGestureDetector) {super.onScaleEnd(detector)if (detector.currentSpan > 50 && detector.timeDelta > 10) {mScaleFactor = detector.scaleFactor}}override fun onScale(detector: ScaleGestureDetector): Boolean {//更新两个手指缩放的中心点。mCenterX = detector.focusXmCenterY = detector.focusYreturn super.onScale(detector)}})}fun setTestImageView(iv: ImageView?) {testIV = iv}private fun updateView() {this.invalidate()}override fun onTouchEvent(event: MotionEvent): Boolean {when (event.actionMasked) {MotionEvent.ACTION_MOVE -> {mScaleGestureDetector?.onTouchEvent(event)mCanDrawCircle = true}MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {mCanDrawScaleBmp = true //两个手指松开了，可以绘制放大的图。mCanDrawCircle = false}}updateView()return true}override fun onDraw(canvas: Canvas) {super.onDraw(canvas)if (mCanDrawCircle) {canvas.drawCircle(mCenterX, mCenterY, 10f, mCirclePaint)}if (mCanDrawScaleBmp) {myDraw(canvas)}}private fun myDraw(canvas: Canvas) {Thread.sleep(1500)if (mScaleBmp == null) {//创建一次，避免重复创建，提高速度。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, 40f, mCirclePaint)}
}
两根手指在原图上缩放，红色小圆圈实时处于两根手指的中心点：
当两根手指离开屏幕后，然后放大原图，并把原先手指中心点“点中”的原图位置，移动到屏幕中心：
Android双击图片放大移动图中双击点到ImageView区域中心，Kotlin-CSDN博客文章浏览阅读663次，点赞14次，收藏17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/135630975
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