How to avoid thread start twice in android?

Before getting into an example, we should know what thread is. A thread is a lightweight sub-process, it going to do background operations without interrupt to ui. This example demonstrate about How to avoid thread start twice 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"?>
<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"
   android:gravity="center_horizontal"
   android:layout_marginTop="100dp"
   tools:context=".MainActivity">
   <EditText
      android:id="@+id/edit_query"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="Enter string" />
   <Button
      android:id="@+id/click"
      android:layout_marginTop="50dp"
      style="@style/Base.TextAppearance.AppCompat.Widget.Button.Borderless.Colored"
      android:layout_width="wrap_content"
      android:background="#c1c1c1"
      android:textColor="#FFF"
      android:layout_height="wrap_content"
      android:text="Button" />
   <TextView
      android:id="@+id/text"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" />
</LinearLayout>

In the above code, we have taken edittext and textview. When user enter some text into edittext, it going to wait till 5000ms and update textview.

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

package com.example.myapplication;

import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
   EditText edit_query;
   TextView textView;
   boolean twice=false;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      edit_query = findViewById(R.id.edit_query);
      textView = findViewById(R.id.text);
      findViewById(R.id.click).setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            runthread();
         }
      });
   }

   private void runthread() {
      twice = true;
      if(twice) {
         final String s1 = edit_query.getText().toString();
         Handler handler = new Handler();
         handler.post(new Runnable() {
            @Override
            public void run() {
               runOnUiThread(new Runnable() {
                  @Override
                  public void run() {
                     textView.setText(s1);
                     try {
                        Thread.sleep(5000);
                        twice = false;
                     } catch (InterruptedException e) {
                        e.printStackTrace();
                     }
                  }
               });
            }
         });
      }
   }
}

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 −

In the above result, Enter some text in edit text and click on the button for twice or thrice, It not going to start a thread, after 5000ms it will update textview and reset thread count to 0.

Click here to download the project code