ScaleGestureDetector example (Android, kotlin)

activity_main.xml

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

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center"
        android:contentDescription="@string/image_editor"
        android:src="@mipmap/ic_launcher" />

</LinearLayout>

MainActivity.kt

package com.example.myapplication

import android.annotation.SuppressLint
import android.os.Bundle
import android.view.ScaleGestureDetector
import androidx.appcompat.app.AppCompatActivity
import com.example.myapplication.databinding.ActivityMainBinding

@SuppressLint("ClickableViewAccessibility")
class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val imageView = binding.imageView
        var scaleFactor = 1f
        val scaleGestureDetector = ScaleGestureDetector(
            this,
            object : ScaleGestureDetector.SimpleOnScaleGestureListener() {
                override fun onScale(detector: ScaleGestureDetector): Boolean {
                    scaleFactor *= detector.scaleFactor
                    scaleFactor = scaleFactor.coerceIn(0.1f, 5.0f)

                    imageView.scaleX = scaleFactor
                    imageView.scaleY = scaleFactor

                    return super.onScale(detector)
                }
            }
        )

        imageView.setOnTouchListener { _, event ->
            scaleGestureDetector.onTouchEvent(event)
        }
    }
}

strings.xml

<resources>
    <string name="app_name">My Application</string>
    <string name="image_editor">Image Editor</string>
</resources>

Thanks for this gist 👏 👏 I was struggling with it for a day 😆