Android How to draw a smooth line following my finger?

This example demonstrates how do I draw a smooth line following my finger in android.

Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.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">
   <ImageView
      android:id="@+id/imageView"
      android:layout_width="wrap_content"
      android:layout_height="match_parent"
      android:layout_alignParentStart="true"
      android:layout_alignParentEnd="true"
      android:layout_alignParentTop="true"
      android:src="@drawable/ic_launcher_foreground" />
</RelativeLayout>

Step 3 − Add the following code to src/MainActivity.java

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
public class MainActivity extends AppCompatActivity implements View.OnTouchListener {
   ImageView imageView;
   Bitmap bitmap;
   Canvas canvas;
   Paint paint;
   float downX = 0, downY = 0, upX = 0, upY = 0;
   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      imageView = this.findViewById(R.id.imageView);
      Display currentDisplay = getWindowManager().getDefaultDisplay();
      float dw = currentDisplay.getWidth();
      float dh = currentDisplay.getHeight();
      bitmap = Bitmap.createBitmap((int) dw, (int) dh,
      Bitmap.Config.ARGB_8888);
      canvas = new Canvas(bitmap);
      paint = new Paint();
      paint.setColor(Color.BLACK);
      imageView.setImageBitmap(bitmap);
      imageView.setOnTouchListener(this);
   }
   public boolean onTouch(View v, MotionEvent event) {
      int action = event.getAction();
      switch (action) {
         case MotionEvent.ACTION_DOWN:
            downX = event.getX();
            downY = event.getY();
            break;
         case MotionEvent.ACTION_MOVE:
            break;
         case MotionEvent.ACTION_UP:
            upX = event.getX();
            upY = event.getY();
            canvas.drawLine(downX, downY, upX, upY, paint);
            imageView.invalidate();
            break;
         case MotionEvent.ACTION_CANCEL:
            break;
         default:
            break;
      }
      return true;
   }
}

Step 4 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="app.com.sample">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
</application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –