Pinch to zoom in android

Today we are going to learn a cool functionality pinch to zoom in android.

1. Firstly You need to show an ImageView in your layout file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:gravity="center"
    android:layout_height="match_parent">


    <ImageView
        android:layout_width="wrap_content"
        android:src="@drawable/sun_rise"
        android:id="@+id/pinch_image"
        android:layout_height="wrap_content"/>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical" android:layout_width="match_parent"

android:gravity="center"

android:layout_height="match_parent">

<ImageView

android:layout_width="wrap_content"

android:src="@drawable/sun_rise"

android:id="@+id/pinch_image"

android:layout_height="wrap_content"/>

</LinearLayout>

2. After that you need to create a class that’s responsible for Gesture Detection:

class ScaleListener internal constructor(private var mImageView: ImageView) :
    SimpleOnScaleGestureListener() {
    private var mScaleFactor = 1.0f

    override fun onScale(scaleGestureDetector: ScaleGestureDetector): Boolean {
        mScaleFactor *= scaleGestureDetector.scaleFactor
        mScaleFactor = Math.max(
            0.1f,
            Math.min(mScaleFactor, 10.0f)
        )
        mImageView.scaleX = mScaleFactor
        mImageView.scaleY = mScaleFactor
        return true
    }

}

class ScaleListener internal constructor(private var mImageView: ImageView) :

SimpleOnScaleGestureListener() {

private var mScaleFactor = 1.0f

override fun onScale(scaleGestureDetector: ScaleGestureDetector): Boolean {

mScaleFactor *= scaleGestureDetector.scaleFactor

mScaleFactor = Math.max(

0.1f,

Math.min(mScaleFactor, 10.0f)

)

mImageView.scaleX = mScaleFactor

mImageView.scaleY = mScaleFactor

return true

}

This class should only be used with MotionEvent’s reported via touch.

4. Initialize Imageview and ScaleGestureDetector:

var imageView:ImageView?= null
var mScaleGestureDetector: ScaleGestureDetector? = null

1 2	var imageView:ImageView?= null var mScaleGestureDetector: ScaleGestureDetector? = null

imageView = findViewById(R.id.pinch_image)

mScaleGestureDetector = ScaleGestureDetector(this, ScaleListener(imageView))

imageView = findViewById(R.id.pinch_image)

mScaleGestureDetector = ScaleGestureDetector(this, ScaleListener(imageView))

5. Override onTouchEvent() as follows:

override fun onTouchEvent(event: MotionEvent?): Boolean {
        mScaleGestureDetector?.onTouchEvent(event)
        return super.onTouchEvent(event)
    }

override fun onTouchEvent(event: MotionEvent?): Boolean {

mScaleGestureDetector?.onTouchEvent(event)

return super.onTouchEvent(event)

}

6. Yes! as a result of above all, we are done, to experiment with the pinch-to-zoom functionality.

Anand Kashyap 28 February 2020

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Pinch to zoom in android