【Android】画像をピンチイン・アウト

Kotlinで書かれているコードが見つからなかったのでメモ。

CustomImageView.kt

class CustomImageView : View {
	constructor(context: Context) : super(context)
	constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
	constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)

	private var bitmap: Bitmap? = null
	private val bitmapMatrix = Matrix()
	private val paint = Paint()

	// ピンチイン/アウト時、画像を拡大/縮小
	private val scaleGestureDetector by lazy {
		ScaleGestureDetector(context, object : SimpleOnScaleGestureListener() {
			private var scale = 1f
			override fun onScaleBegin(detector: ScaleGestureDetector?): Boolean {
				scale = 1f
				return super.onScaleBegin(detector)
			}

			override fun onScale(detector: ScaleGestureDetector): Boolean {
				val deltaScale = detector.scaleFactor / scale
				bitmapMatrix.postScale(deltaScale, deltaScale, detector.focusX, detector.focusY)
				scale = detector.scaleFactor
				invalidate()
				return super.onScale(detector)
			}
		})
	}

	//スクロール時、画像を移動
	private val gestureDetector by lazy {
		GestureDetector(context, object : SimpleOnGestureListener() {
			override fun onScroll(e1: MotionEvent, e2: MotionEvent, distanceX: Float, distanceY: Float): Boolean {
				if (e1.getPointerId(0) == e2.getPointerId(0)) {
					bitmapMatrix.postTranslate(-distanceX, -distanceY)
					invalidate()
				}
				return super.onScroll(e1, e2, distanceX, distanceY)
			}
		})
	}

	@SuppressLint("ClickableViewAccessibility")
	override fun onTouchEvent(event: MotionEvent): Boolean {
		return gestureDetector.onTouchEvent(event) || scaleGestureDetector.onTouchEvent(event) || super.onTouchEvent(event)
	}

	override fun onDraw(canvas: Canvas) {
		bitmap?.let { bitmap ->
			canvas.save()
			canvas.drawBitmap(bitmap, bitmapMatrix, paint)
			canvas.restore()
		}
	}

	/**
	 * ビットマップをセット
	 *
	 * @param bitmap ビットマップ
	 */
	fun setBitmap(bitmap: Bitmap?) {
		if (bitmap != null) {
			this.bitmap = bitmap
			val mScaleFactor = min(width.toFloat() / bitmap.width, height.toFloat() / bitmap.height)
			bitmapMatrix.setScale(mScaleFactor, mScaleFactor, 0f, 0f)
		}
	}
}

参照記事：https://qiita.com/Cyber_Hacnosuke/items/b2a8724218d2f4a4c3c2