Android Image View Pinch Zooming
Using a ScaleGestureDetector
When learning a new concept I don't like using libraries or code dumps. I found a good description here and in the documentation of how to resize an image by pinching. This answer is a slightly modified summary. You will probably want to add more functionality later, but it will help you get started.
Layout
The ImageView just uses the app logo since it is already available. You can replace it with any image you like, though.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="@+id/imageView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:src="@mipmap/ic_launcher"
android:layout_centerInParent="true"/>
</RelativeLayout>
Activity
We use a ScaleGestureDetector on the activity to listen to touch events. When a scale (ie, pinch) gesture is detected, then the scale factor is used to resize the ImageView.
public class MainActivity extends AppCompatActivity {
private ScaleGestureDetector mScaleGestureDetector;
private float mScaleFactor = 1.0f;
private ImageView mImageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// initialize the view and the gesture detector
mImageView = findViewById(R.id.imageView);
mScaleGestureDetector = new ScaleGestureDetector(this, new ScaleListener());
}
// this redirects all touch events in the activity to the gesture detector
@Override
public boolean onTouchEvent(MotionEvent event) {
return mScaleGestureDetector.onTouchEvent(event);
}
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
// when a scale gesture is detected, use it to resize the image
@Override
public boolean onScale(ScaleGestureDetector scaleGestureDetector){
mScaleFactor *= scaleGestureDetector.getScaleFactor();
mImageView.setScaleX(mScaleFactor);
mImageView.setScaleY(mScaleFactor);
return true;
}
}
}
Notes
- Although the activity had the gesture detector in the example above, it could have also been set on the image view itself.
You can limit the size of the scaling with something like
mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f));Thanks again to Pinch-to-zoom with multi-touch gestures In Android
- Documentation
- Use Ctrl + mouse drag to simulate a pinch gesture in the emulator.
Going on
You will probably want to do other things like panning and scaling to some focus point. You can develop these things yourself, but if you would like to use a pre-made custom view, copy TouchImageView.java into your project and use it like a normal ImageView. It worked well for me and I only ran into one bug. I plan to further edit the code to remove the warning and the parts that I don't need. You can do the same.
You can use this class : TouchImageView
Add bellow line in build.gradle:
compile 'com.commit451:PhotoView:1.2.4'
or
compile 'com.github.chrisbanes:PhotoView:1.3.0'
In Java file:
PhotoViewAttacher photoAttacher;
photoAttacher= new PhotoViewAttacher(Your_Image_View);
photoAttacher.update();
I made my own custom imageview with pinch to zoom. There is no limits/borders on Chirag Ravals code, so user can drag the image off the screen. This will fix it.
Here is the CustomImageView class:
public class CustomImageVIew extends ImageView implements OnTouchListener {
private Matrix matrix = new Matrix();
private Matrix savedMatrix = new Matrix();
static final int NONE = 0;
static final int DRAG = 1;
static final int ZOOM = 2;
private int mode = NONE;
private PointF mStartPoint = new PointF();
private PointF mMiddlePoint = new PointF();
private Point mBitmapMiddlePoint = new Point();
private float oldDist = 1f;
private float matrixValues[] = {0f, 0f, 0f, 0f, 0f, 0f, 0f, 0f, 0f};
private float scale;
private float oldEventX = 0;
private float oldEventY = 0;
private float oldStartPointX = 0;
private float oldStartPointY = 0;
private int mViewWidth = -1;
private int mViewHeight = -1;
private int mBitmapWidth = -1;
private int mBitmapHeight = -1;
private boolean mDraggable = false;
public CustomImageVIew(Context context) {
this(context, null, 0);
}
public CustomImageVIew(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public CustomImageVIew(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
this.setOnTouchListener(this);
}
@Override
public void onSizeChanged (int w, int h, int oldw, int oldh){
super.onSizeChanged(w, h, oldw, oldh);
mViewWidth = w;
mViewHeight = h;
}
public void setBitmap(Bitmap bitmap){
if(bitmap != null){
setImageBitmap(bitmap);
mBitmapWidth = bitmap.getWidth();
mBitmapHeight = bitmap.getHeight();
mBitmapMiddlePoint.x = (mViewWidth / 2) - (mBitmapWidth / 2);
mBitmapMiddlePoint.y = (mViewHeight / 2) - (mBitmapHeight / 2);
matrix.postTranslate(mBitmapMiddlePoint.x, mBitmapMiddlePoint.y);
this.setImageMatrix(matrix);
}
}
@Override
public boolean onTouch(View v, MotionEvent event){
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
savedMatrix.set(matrix);
mStartPoint.set(event.getX(), event.getY());
mode = DRAG;
break;
case MotionEvent.ACTION_POINTER_DOWN:
oldDist = spacing(event);
if(oldDist > 10f){
savedMatrix.set(matrix);
midPoint(mMiddlePoint, event);
mode = ZOOM;
}
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_POINTER_UP:
mode = NONE;
break;
case MotionEvent.ACTION_MOVE:
if(mode == DRAG){
drag(event);
} else if(mode == ZOOM){
zoom(event);
}
break;
}
return true;
}
public void drag(MotionEvent event){
matrix.getValues(matrixValues);
float left = matrixValues[2];
float top = matrixValues[5];
float bottom = (top + (matrixValues[0] * mBitmapHeight)) - mViewHeight;
float right = (left + (matrixValues[0] * mBitmapWidth)) -mViewWidth;
float eventX = event.getX();
float eventY = event.getY();
float spacingX = eventX - mStartPoint.x;
float spacingY = eventY - mStartPoint.y;
float newPositionLeft = (left < 0 ? spacingX : spacingX * -1) + left;
float newPositionRight = (spacingX) + right;
float newPositionTop = (top < 0 ? spacingY : spacingY * -1) + top;
float newPositionBottom = (spacingY) + bottom;
boolean x = true;
boolean y = true;
if(newPositionRight < 0.0f || newPositionLeft > 0.0f){
if(newPositionRight < 0.0f && newPositionLeft > 0.0f){
x = false;
} else{
eventX = oldEventX;
mStartPoint.x = oldStartPointX;
}
}
if(newPositionBottom < 0.0f || newPositionTop > 0.0f){
if(newPositionBottom < 0.0f && newPositionTop > 0.0f){
y = false;
} else{
eventY = oldEventY;
mStartPoint.y = oldStartPointY;
}
}
if(mDraggable){
matrix.set(savedMatrix);
matrix.postTranslate(x? eventX - mStartPoint.x : 0, y? eventY - mStartPoint.y : 0);
this.setImageMatrix(matrix);
if(x)oldEventX = eventX;
if(y)oldEventY = eventY;
if(x)oldStartPointX = mStartPoint.x;
if(y)oldStartPointY = mStartPoint.y;
}
}
public void zoom(MotionEvent event){
matrix.getValues(matrixValues);
float newDist = spacing(event);
float bitmapWidth = matrixValues[0] * mBitmapWidth;
float bimtapHeight = matrixValues[0] * mBitmapHeight;
boolean in = newDist > oldDist;
if(!in && matrixValues[0] < 1){
return;
}
if(bitmapWidth > mViewWidth || bimtapHeight > mViewHeight){
mDraggable = true;
} else{
mDraggable = false;
}
float midX = (mViewWidth / 2);
float midY = (mViewHeight / 2);
matrix.set(savedMatrix);
scale = newDist / oldDist;
matrix.postScale(scale, scale, bitmapWidth > mViewWidth ? mMiddlePoint.x : midX, bimtapHeight > mViewHeight ? mMiddlePoint.y : midY);
this.setImageMatrix(matrix);
}
/** Determine the space between the first two fingers */
private float spacing(MotionEvent event) {
float x = event.getX(0) - event.getX(1);
float y = event.getY(0) - event.getY(1);
return (float)Math.sqrt(x * x + y * y);
}
/** Calculate the mid point of the first two fingers */
private void midPoint(PointF point, MotionEvent event) {
float x = event.getX(0) + event.getX(1);
float y = event.getY(0) + event.getY(1);
point.set(x / 2, y / 2);
}
}
This is how you can use it in your activity:
CustomImageVIew mImageView = (CustomImageVIew)findViewById(R.id.customImageVIew1);
mImage.setBitmap(your bitmap);
And layout:
<your.package.name.CustomImageVIew
android:id="@+id/customImageVIew1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_marginBottom="15dp"
android:layout_marginLeft="15dp"
android:layout_marginRight="15dp"
android:layout_marginTop="15dp"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:scaleType="matrix"/> // important