Can we use scale gesture detector for pinch zoom in Android?
Can we use scale gesture detector for pinch zoom in Android?
You can use this
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
public class MyImageView extends View {
private static final int INVALID_POINTER_ID = -1;
private Drawable mImage;
private float mPosX;
private float mPosY;
private float mLastTouchX;
private float mLastTouchY;
private int mActivePointerId = INVALID_POINTER_ID;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
public MyImageView(Context context) {
this(context, null, 0);
mImage=act.getResources().getDrawable(context.getResources().getIdentifier("imagename", "drawable", "packagename"));
mImage.setBounds(0, 0, mImage.getIntrinsicWidth(), mImage.getIntrinsicHeight());
}
public MyImageView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public MyImageView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
// Let the ScaleGestureDetector inspect all events.
mScaleDetector.onTouchEvent(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
// Only move if the ScaleGestureDetector isn't processing a gesture.
if (!mScaleDetector.isInProgress()) {
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
invalidate();
}
mLastTouchX = x;
mLastTouchY = y;
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK)
>> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
Log.d("DEBUG", "X: "+mPosX+" Y: "+mPosY);
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
mImage.draw(canvas);
canvas.restore();
}
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
@Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));
invalidate();
return true;
}
}
}
to call this in your activity.setContentView(new MyImageView(this));
You can create a reusable class that implements OnTouchListener to accomplish this.
public class MyScaleGestures implements OnTouchListener, OnScaleGestureListener {
private View view;
private ScaleGestureDetector gestureScale;
private float scaleFactor = 1;
private boolean inScale = false;
public MyScaleGestures (Context c){ gestureScale = new ScaleGestureDetector(c, this); }
@Override
public boolean onTouch(View view, MotionEvent event) {
this.view = view;
gestureScale.onTouchEvent(event);
return true;
}
@Override
public boolean onScale(ScaleGestureDetector detector) {
scaleFactor *= detector.getScaleFactor();
scaleFactor = (scaleFactor < 1 ? 1 : scaleFactor); // prevent our view from becoming too small //
scaleFactor = ((float)((int)(scaleFactor * 100))) / 100; // Change precision to help with jitter when user just rests their fingers //
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
return true;
}
@Override
public boolean onScaleBegin(ScaleGestureDetector detector) {
inScale = true;
return true;
}
@Override
public void onScaleEnd(ScaleGestureDetector detector) { inScale = false; }
}
Then assign it as your View's OnTouchListener like so.
myView.setOnTouchListener(new MyScaleGestures(context));
If you want to add a scrolling ability to the View you will need to implement onScroll from the OnGestureListener interface. You can add this override to the MyScaleGestures class to accomplish this.
@Override
public boolean onScroll(MotionEvent event1, MotionEvent event2, float x, float y) {
float newX = view.getX();
float newY = view.getY();
if(!inScale){
newX -= x;
newY -= y;
}
WindowManager wm = (WindowManager) view.getContext().getSystemService(Context.WINDOW_SERVICE);
Display d = wm.getDefaultDisplay();
Point p = new Point();
d.getSize(p);
if (newX > (view.getWidth() * scaleFactor - p.x) / 2){
newX = (view.getWidth() * scaleFactor - p.x) / 2;
} else if (newX < -((view.getWidth() * scaleFactor - p.x) / 2)){
newX = -((view.getWidth() * scaleFactor - p.x) / 2);
}
if (newY > (view.getHeight() * scaleFactor - p.y) / 2){
newY = (view.getHeight() * scaleFactor - p.y) / 2;
} else if (newY < -((view.getHeight() * scaleFactor - p.y) / 2)){
newY = -((view.getHeight() * scaleFactor - p.y) / 2);
}
view.setX(newX);
view.setY(newY);
return true;
}
The end result of doing all of the above will give you class like this one:
public class StandardGestures implements OnTouchListener, OnGestureListener, OnDoubleTapListener, OnScaleGestureListener {
private View view;
private GestureDetector gesture;
private ScaleGestureDetector gestureScale;
private float scaleFactor = 1;
private boolean inScale;
public StandardGestures(Context c){
gesture = new GestureDetector(c, this);
gestureScale = new ScaleGestureDetector(c, this);
}
@Override
public boolean onTouch(View view, MotionEvent event) {
this.view = view;
gesture.onTouchEvent(event);
gestureScale.onTouchEvent(event);
return true;
}
@Override
public boolean onDown(MotionEvent event) {
return true;
}
@Override
public boolean onFling(MotionEvent event1, MotionEvent event2, float x, float y) {
return true;
}
@Override
public void onLongPress(MotionEvent event) {
}
@Override
public boolean onScroll(MotionEvent event1, MotionEvent event2, float x, float y) {
float newX = view.getX();
float newY = view.getY();
if(!inScale){
newX -= x;
newY -= y;
}
WindowManager wm = (WindowManager) view.getContext().getSystemService(Context.WINDOW_SERVICE);
Display d = wm.getDefaultDisplay();
Point p = new Point();
d.getSize(p);
if (newX > (view.getWidth() * scaleFactor - p.x) / 2){
newX = (view.getWidth() * scaleFactor - p.x) / 2;
} else if (newX < -((view.getWidth() * scaleFactor - p.x) / 2)){
newX = -((view.getWidth() * scaleFactor - p.x) / 2);
}
if (newY > (view.getHeight() * scaleFactor - p.y) / 2){
newY = (view.getHeight() * scaleFactor - p.y) / 2;
} else if (newY < -((view.getHeight() * scaleFactor - p.y) / 2)){
newY = -((view.getHeight() * scaleFactor - p.y) / 2);
}
view.setX(newX);
view.setY(newY);
return true;
}
@Override
public void onShowPress(MotionEvent event) {
}
@Override
public boolean onSingleTapUp(MotionEvent event) {
return true;
}
@Override
public boolean onDoubleTap(MotionEvent event) {
view.setVisibility(View.GONE);
return true;
}
@Override
public boolean onDoubleTapEvent(MotionEvent event) {
return true;
}
@Override
public boolean onSingleTapConfirmed(MotionEvent event) {
return true;
}
@Override
public boolean onScale(ScaleGestureDetector detector) {
scaleFactor *= detector.getScaleFactor();
scaleFactor = scaleFactor < 1 ? 1 : scaleFactor; // prevent our image from becoming too small
scaleFactor = (float) (int) (scaleFactor * 100) / 100; // Change precision to help with jitter when user just rests their fingers //
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
onScroll(null, null, 0, 0); // call scroll to make sure our bounds are still ok //
return true;
}
@Override
public boolean onScaleBegin(ScaleGestureDetector detector) {
inScale = true;
return true;
}
@Override
public void onScaleEnd(ScaleGestureDetector detector) {
inScale = false;
onScroll(null, null, 0, 0); // call scroll to make sure our bounds are still ok //
}
}