Pinch-zoomable Android frame layout with functionality to move child view inside parent boundaries

ZoomMoveLayout.java

/**
 * Adapted from anorth at https://gist.github.com/anorth/9845602.
 * by Ahmed Mousa on Feb 14 - 2018.
 */

import android.content.Context;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.FrameLayout;

/**
*Pinch-zoomable Android frame layout with functionality to move it's child inside it's boundaries
*/
public class ZoomMoveLayout extends FrameLayout implements ScaleGestureDetector.OnScaleGestureListener {

    private enum Mode {
        NONE,
        DRAG,
        ZOOM
    }

    private static final String TAG = "ZoomMoveLayout";
    private static final float MIN_ZOOM = 0.6f;
    private float maxZoom;

    private Mode mode = Mode.NONE;
    private float scale = 1.0f;

    // Where the finger first  touches the screen
    private float startX = 0f;
    private float startY = 0f;

    // How much to translate the canvas
    private float dx = 0f;
    private float dy = 0f;
    private float prevDx = 0f;
    private float prevDy = 0f;

    private ScaleGestureDetector scaleDetector;
    private GestureDetector singleTapDetector;
    private OnClickListener onSingleTabClick;

    public ZoomMoveLayout(Context context) {
        super(context);
        init(context);
    }

    public ZoomMoveLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public ZoomMoveLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context);
    }

    private void init(Context context) {
        scaleDetector  = new ScaleGestureDetector(context, this);
        singleTapDetector = new GestureDetector(context, new SingleTapConfirm());
    }

    public void setOnSingleTabClick(OnClickListener onSingleTabClick){
        this.onSingleTabClick = onSingleTabClick;
    }

    private class SingleTapConfirm extends GestureDetector.SimpleOnGestureListener {

        @Override
        public boolean onSingleTapUp(MotionEvent event) {
            return true;
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent motionEvent) {

        //if one click
        if (singleTapDetector.onTouchEvent(motionEvent) && onSingleTabClick != null)
            onSingleTabClick.onClick(this);
        else {
            //move and drag
            switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {

                case MotionEvent.ACTION_DOWN:
                    mode = Mode.DRAG;
                    startX = motionEvent.getX() - prevDx;
                    startY = motionEvent.getY() - prevDy;
                    break;
                case MotionEvent.ACTION_MOVE:
                    if (mode == Mode.DRAG) {
                        dx = motionEvent.getX() - startX;
                        dy = motionEvent.getY() - startY;
                    }
                    break;
                case MotionEvent.ACTION_POINTER_DOWN:
                    mode = Mode.ZOOM;
                    break;
                case MotionEvent.ACTION_POINTER_UP:
                    mode = Mode.NONE;
                    break;
                case MotionEvent.ACTION_UP:
                    mode = Mode.NONE;
                    prevDx = dx;
                    prevDy = dy;
                    break;
            }

            scaleDetector.onTouchEvent(motionEvent);

            if (mode == Mode.DRAG || mode == Mode.ZOOM) {
                getParent().requestDisallowInterceptTouchEvent(true);
                applyScaleAndTranslation();
            }
        }

        return true;
    }

    private void applyScaleAndTranslation() {
        child().setScaleX(scale);
        child().setScaleY(scale);

        child().animate().translationX(getPosX()).translationY(getPosY()).setDuration(0).withLayer().start();

        invalidate();
    }

    private void setScaleValue(float newScale){
        scale *= newScale;
        scale = Math.max(MIN_ZOOM, Math.min(scale, getMaxZoom()));
    }

    private float getMaxZoom(){
        if (maxZoom == 0.0f) {
            //ratio according to width
            float ratio = (float) child().getWidth() / child().getHeight();

            // 1.7 our aspect ration 16/9
            if (ratio >= ((float) 16/9))
                maxZoom = (float) getWidth() / child().getWidth();
            else
                maxZoom = (float) getHeight() / child().getHeight();
        }
        return maxZoom;
    }

    private float getPosX(){
        if (dx > getBoundaryRight()) dx = getBoundaryRight();
        else if (dx < getBoundaryLeft()) dx = getBoundaryLeft();

        return dx;
    }

    private float getPosY(){
        if (dy < getBoundaryTop()) dy = getBoundaryTop();
        else if (dy > getBoundaryBottom()) dy = getBoundaryBottom();

        return dy;
    }

    private float getBoundaryRight(){
        return getRight() - child().getRight() - getChildScaledX();
    }

    private float getBoundaryBottom(){return getBottom() - child().getBottom() - getChildScaledY();}

    public float getBoundaryLeft() {
        return getLeft() - child().getLeft() + getChildScaledX();
    }

    public float getBoundaryTop() {
        return getTop() - child().getTop() + getChildScaledY();
    }

    private View child() {
        return getChildAt(0);
    }

    private float getChildScaledX(){ return (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;}

    private float getChildScaledY(){ return (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;}

    public float getChildPosX(){
        return child().getX() - getChildScaledX();
    }

    public float getChildPosY(){
        return child().getY() - getChildScaledY();
    }

    public int getChildScaledWidth(){return (int) (child().getWidth() * scale);}

    public int getChildScaledHeight(){
        return (int) (child().getHeight() * scale);
    }

    // ScaleGestureDetector
    @Override
    public boolean onScaleBegin(ScaleGestureDetector scaleDetector) {
        return true;
    }

    @Override
    public boolean onScale(ScaleGestureDetector scaleDetector) {
        setScaleValue(scaleDetector.getScaleFactor());
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector scaleDetector) {}
}