Zoom Scroll View in Android

In this article, we are going to implement zoom on ScrollView. Most of the time when we create a scroll view then it contains a lot of data and if we want to view any content on zooming then we can implement this feature. This feature can be useful when we are scroll in an App and that contains data using RecyclerView. There we can implement this feature to see the data inside RecyclerView by zoom in. A sample GIF is given below to get an idea about what we are going to do in this article. Note that we are going to implement this project using the Java language. 

Step by Step Implementation

Step 1: Create a New Project

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Java as the programming language.

Step 2: Working with the activity_main.xml file

Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file. 

XML

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

    <ScrollView
        android:id="@+id/scrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#1B5E20">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Zoom Scroll View"
            android:textSize="32sp" />

    </ScrollView>

</RelativeLayout>

Step 3: Working with the MainActivity.java file

Below is the code for the implementation of this feature.

// implementation of this feature
mScaleGestureDetector = new ScaleGestureDetector(this, new ScaleGestureDetector.SimpleOnScaleGestureListener(){
            @Override
            public boolean onScale(ScaleGestureDetector detector) {
                // firstly we will get the scale factor by which we want to zoom
                float scale = 1 - detector.getScaleFactor();
                float prevScale = mScale;
                mScale += scale;
                
                // we can maximise our focus to 10f only
                if (mScale > 10f)
                    mScale = 10f;
              
                ScaleAnimation scaleAnimation = new ScaleAnimation(1f / prevScale, 1f / mScale, 1f / prevScale, 1f / mScale, detector.getFocusX(), detector.getFocusY());
                
                // duration of animation will be 0.It will not change by self after that  
                scaleAnimation.setDuration(0);
               
                scaleAnimation.setFillAfter(true);
              
                // initialising the scrollview
                ScrollView layout = (ScrollView) findViewById(R.id.scrollView);
                
                // we are setting it as animation
                layout.startAnimation(scaleAnimation);
                return true;
       }
  });

Below is the complete code for the MainActivity.java file. Comments are added inside the code to understand the code in more detail.

Java

import android.os.Bundle;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.animation.ScaleAnimation;
import android.widget.ScrollView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private float mScale = 1f;
    private ScaleGestureDetector mScaleGestureDetector;
    GestureDetector gestureDetector;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // initialising the values
        gestureDetector = new GestureDetector(this, new GestureListener());
        mScaleGestureDetector = new ScaleGestureDetector(this, new ScaleGestureDetector.SimpleOnScaleGestureListener() {
            @Override
            public boolean onScale(ScaleGestureDetector detector) {

                // firstly we will get the scale factor
                float scale = 1 - detector.getScaleFactor();
                float prevScale = mScale;
                mScale += scale;

                // we can maximise our focus to 10f only
                if (mScale > 10f)
                    mScale = 10f;

                ScaleAnimation scaleAnimation = new ScaleAnimation(1f / prevScale, 1f / mScale, 1f / prevScale, 1f / mScale, detector.getFocusX(), detector.getFocusY());

                // duration of animation will be 0.It will
                // not change by self after that
                scaleAnimation.setDuration(0);
                scaleAnimation.setFillAfter(true);

                // initialising the scrollview
                ScrollView layout = (ScrollView) findViewById(R.id.scrollView);

                // we are setting it as animation
                layout.startAnimation(scaleAnimation);
                return true;
            }
        });
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        super.dispatchTouchEvent(event);

        // special types of touch screen events such as pinch ,
        // double tap, scrolls , long presses and flinch,
        // onTouch event is called if found any of these
        mScaleGestureDetector.onTouchEvent(event);
        gestureDetector.onTouchEvent(event);
        return gestureDetector.onTouchEvent(event);
    }

    private class GestureListener extends GestureDetector.SimpleOnGestureListener {
        @Override
        public boolean onDown(MotionEvent e) {
            return true;
        }

        @Override
        public boolean onDoubleTap(MotionEvent e) {
            return true;
        }
    }
}

Output: