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@anorth
Created March 29, 2014 00:06
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Pinch-zoomable Android frame layout
package au.id.alexn;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.FrameLayout;
/**
* Layout that provides pinch-zooming of content. This view should have exactly one child
* view containing the content.
*/
public class ZoomLayout extends FrameLayout implements ScaleGestureDetector.OnScaleGestureListener {
private enum Mode {
NONE,
DRAG,
ZOOM
}
private static final String TAG = "ZoomLayout";
private static final float MIN_ZOOM = 1.0f;
private static final float MAX_ZOOM = 4.0f;
private Mode mode = Mode.NONE;
private float scale = 1.0f;
private float lastScaleFactor = 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;
public ZoomLayout(Context context) {
super(context);
init(context);
}
public ZoomLayout(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public ZoomLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
private void init(Context context) {
final ScaleGestureDetector scaleDetector = new ScaleGestureDetector(context, this);
this.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
Log.i(TAG, "DOWN");
if (scale > MIN_ZOOM) {
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.DRAG;
break;
case MotionEvent.ACTION_UP:
Log.i(TAG, "UP");
mode = Mode.NONE;
prevDx = dx;
prevDy = dy;
break;
}
scaleDetector.onTouchEvent(motionEvent);
if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
getParent().requestDisallowInterceptTouchEvent(true);
float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
dx = Math.min(Math.max(dx, -maxDx), maxDx);
dy = Math.min(Math.max(dy, -maxDy), maxDy);
Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
+ ", max " + maxDx);
applyScaleAndTranslation();
}
return true;
}
});
}
// ScaleGestureDetector
@Override
public boolean onScaleBegin(ScaleGestureDetector scaleDetector) {
Log.i(TAG, "onScaleBegin");
return true;
}
@Override
public boolean onScale(ScaleGestureDetector scaleDetector) {
float scaleFactor = scaleDetector.getScaleFactor();
Log.i(TAG, "onScale" + scaleFactor);
if (lastScaleFactor == 0 || (Math.signum(scaleFactor) == Math.signum(lastScaleFactor))) {
scale *= scaleFactor;
scale = Math.max(MIN_ZOOM, Math.min(scale, MAX_ZOOM));
lastScaleFactor = scaleFactor;
} else {
lastScaleFactor = 0;
}
return true;
}
@Override
public void onScaleEnd(ScaleGestureDetector scaleDetector) {
Log.i(TAG, "onScaleEnd");
}
private void applyScaleAndTranslation() {
child().setScaleX(scale);
child().setScaleY(scale);
child().setTranslationX(dx);
child().setTranslationY(dy);
}
private View child() {
return getChildAt(0);
}
}
@totenhund
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To drag without having to zoom

You have to change

 case MotionEvent.ACTION_DOWN:
                        Log.i(TAG, "DOWN");
                        if (scale > MIN_ZOOM) {
                            Log.e("DOWN","Drag");
                            mode = Mode.DRAG;
                            startX = motionEvent.getX() - prevDx;
                            startY = motionEvent.getY() - prevDy;
                        }
                        break;

To

                        Log.i(TAG, "DOWN");
                        // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                        /*if (scale > MIN_ZOOM) {*/
                            Log.e("DOWN","Drag");
                            mode = Mode.DRAG;
                            startX = motionEvent.getX() - prevDx;
                            startY = motionEvent.getY() - prevDy;
                        /*}*/
                        break;

And

                    getParent().requestDisallowInterceptTouchEvent(true);
                    float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
                    float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
                    dx = Math.min(Math.max(dx, -maxDx), maxDx);
                    dy = Math.min(Math.max(dy, -maxDy), maxDy);
                    Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
                            + ", max " + maxDx);
                    applyScaleAndTranslation();
                }

To

if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
                    getParent().requestDisallowInterceptTouchEvent(true);
                    float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
                    float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
                    /*dx = Math.min(Math.max(dx, -maxDx), maxDx);
                    dy = Math.min(Math.max(dy, -maxDy), maxDy);*/
                    Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
                            + ", max " + maxDx);
                    applyScaleAndTranslation();
                }

Full Code

public boolean onTouch(View view, MotionEvent motionEvent) {
                switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
                    case MotionEvent.ACTION_DOWN:
                        Log.i(TAG, "DOWN");
                        // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                        /*if (scale > MIN_ZOOM) {*/
                            Log.e("DOWN","Drag");
                            mode = Mode.DRAG;
                            startX = motionEvent.getX() - prevDx;
                            startY = motionEvent.getY() - prevDy;
                        /*}*/
                        break;
                    case MotionEvent.ACTION_MOVE:
                        if (mode == Mode.DRAG) {
                            Log.e("MOVE","Drag");
                            dx = motionEvent.getX() - startX;
                            dy = motionEvent.getY() - startY;
                        }
                        break;
                    case MotionEvent.ACTION_POINTER_DOWN:
                        mode = Mode.ZOOM;
                        break;
                    // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                    /*case MotionEvent.ACTION_POINTER_UP:mode = Mode.DRAG;*/
                    case MotionEvent.ACTION_POINTER_UP: mode = Mode.NONE;
                        Log.e("ACTION_POINTER_UP","Drag");
                        break;

                    case MotionEvent.ACTION_UP:
                        Log.i(TAG, "UP");
                        Log.e("ACTION_UP","None");
                        mode = Mode.NONE;
                        prevDx = dx;
                        prevDy = dy;
                        break;
                }
                scaleDetector.onTouchEvent(motionEvent);

                if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
                    getParent().requestDisallowInterceptTouchEvent(true);
                    float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
                    float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
                    // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                    /*dx = Math.min(Math.max(dx, -maxDx), maxDx);
                    dy = Math.min(Math.max(dy, -maxDy), maxDy);*/
                    Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
                            + ", max " + maxDx);
                    applyScaleAndTranslation();
                }

                return true;
            }

How to set boundaries for drag?

@vempatissn
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Pan is compulsorily required when we zoom. Both functions are provided in a single class. Great tutorial. Thank you anorth for the post.

@wangtsung
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not working below android 7.0

@shivammonga
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zooming and panning is not working with mouse. how can i do that?

@jacklai24
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I am facing a problem if the zoom layout includes a landscape image. It will leave space at the top and bottom. When I zoom and drag the image. It will be outside the top or bottom boundary. How to calculate the correct "maxDy" in this case?

@AlexEkaterinin
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It works perfectly, thank you very much!

@chensmic
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chensmic commented Oct 2, 2023 via email

@hanzlasheikh
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How can we reset the zoom?

@Nishchay2211
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Hi how can we achieve the focus zoom in this code? I mean when ever we zoom the image it always zoom from center. If we want to zoom and see a specific part of image it doesn't work. I try making use of "getFocusX() & getFocusY()" but it is still not zooming on the focused position but always to centre.

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