ZoomableImageView in Android

ZoomableImageView in Android

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.ImageView;

public class ZoomableImageView extends ImageView {

    private ScaleGestureDetector scaleGestureDetector;
    private Matrix matrix = new Matrix();
    private PointF lastTouchPoint = new PointF();
    private float[] matrixValues = new float[9];

    public ZoomableImageView(Context context) {
        super(context);
        setup(context);
    }

    public ZoomableImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setup(context);
    }

    public ZoomableImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setup(context);
    }

    private void setup(Context context) {
        setScaleType(ScaleType.MATRIX);

        scaleGestureDetector = new ScaleGestureDetector(context, new ScaleGestureDetector.SimpleOnScaleGestureListener() {
            @Override
            public boolean onScale(ScaleGestureDetector detector) {
                float scaleFactor = detector.getScaleFactor();
                matrix.postScale(scaleFactor, scaleFactor, detector.getFocusX(), detector.getFocusY());
                setImageMatrix(matrix);
                return true;
            }
        });
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        scaleGestureDetector.onTouchEvent(event);

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                lastTouchPoint.set(event.getX(), event.getY());
                break;

            case MotionEvent.ACTION_MOVE:
                float deltaX = event.getX() - lastTouchPoint.x;
                float deltaY = event.getY() - lastTouchPoint.y;
                matrix.getValues(matrixValues);
                float scale = matrixValues[Matrix.MSCALE_X];
                float translateX = matrixValues[Matrix.MTRANS_X];
                float translateY = matrixValues[Matrix.MTRANS_Y];
                float imageWidth = getDrawable().getIntrinsicWidth() * scale;
                float imageHeight = getDrawable().getIntrinsicHeight() * scale;

                if (imageWidth < getWidth()) {
                    deltaX = 0;
                    translateX = getWidth() / 2 - imageWidth / 2;
                } else if (translateX + deltaX > 0) {
                    deltaX = -translateX;
                } else if (translateX + deltaX < getWidth() - imageWidth) {
                    deltaX = getWidth() - imageWidth - translateX;
                }

                if (imageHeight < getHeight()) {
                    deltaY = 0;
                    translateY = getHeight() / 2 - imageHeight / 2;
                } else if (translateY + deltaY > 0) {
                    deltaY = -translateY;
                } else if (translateY + deltaY < getHeight() - imageHeight) {
                    deltaY = getHeight() - imageHeight - translateY;
                }

                matrix.postTranslate(deltaX, deltaY);
                lastTouchPoint.set(event.getX(), event.getY());
                setImageMatrix(matrix);
                break;

            case MotionEvent.ACTION_UP:
                break;
        }

        return true;
    }

    public void rotate(float degrees) {
        matrix.postRotate(degrees, getWidth() / 2f, getHeight() / 2f);
        setImageMatrix(matrix);
    }

}