Zoom In and Out to TextView in Android

In this article, we are going to implement the zoom in and zoom out feature in TextView. As we zoom we will see the image after zoom in. Basically, we are going to learn how to increase or decrease the text size in android. 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

Go to the activity_main.xml file and refer to the following code. Below is the code for the activity_main.xml file.

XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/zoomin"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="40dp"
        android:gravity="center"
        android:text="GeeksForGeeks"
        android:textColor="#CE1D59"
        android:textSize="32sp" />

</LinearLayout>

Step 3: Working with the MainActivity.java file

Go to the MainActivity.java file and refer to the following code. Below is the 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.MotionEvent;
import android.view.View;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {

    TextView text;
    final static float move = 200;
    float ratio = 1.0f;
    int bastDst;
    float baseratio;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        text = findViewById(R.id.zoomin);
        text.setTextSize(ratio + 15);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (event.getPointerCount() == 2) {
            int action = event.getAction();
            int mainaction = action & MotionEvent.ACTION_MASK;
            if (mainaction == MotionEvent.ACTION_POINTER_DOWN) {
                bastDst = getDistance(event);
                baseratio = ratio;
            } else {
                // if ACTION_POINTER_UP then after finding the distance
                // we will increase the text size by 15
                float scale = (getDistance(event) - bastDst) / move;
                float factor = (float) Math.pow(2, scale);
                ratio = Math.min(1024.0f, Math.max(0.1f, baseratio * factor));
                text.setTextSize(ratio + 15);
            }
        }
        return true;
    }

    // get distance between the touch event
    private int getDistance(MotionEvent event) {
        int dx = (int) (event.getX(0) - event.getX(1));
        int dy = (int) (event.getY(0) - event.getY(1));
        return (int) Math.sqrt(dx * dx + dy * dy);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        return false;
    }
}

Output: