Use Singleton with Global Context in Android

Before getting into example, we should know what singleton design patter is. A singleton is a design pattern that restricts the instantiation of a class to only one instance. Notable uses include controlling concurrency, and creating a central point of access for an application to access its data store.

This example demonstrates How to use Singleton with Global Context 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"
   tools:context>".MainActivity"
   android:orientation>"vertical">
   <Button
      android:id>"@+id/show"
      android:text>"start dialog in singleTone"
      android:layout_width>"wrap_content"
      android:layout_height>"wrap_content" />
</LinearLayout>

In the above code, we have taken a button. When user click on show button, it will show toast using global context

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

package com.example.andy.myapplication;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
   Button show;
   singleTonExample singletonexample;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      show = findViewById(R.id.show);
      singletonexample = singleTonExample.getInstance();
      singletonexample.init(getApplicationContext());
      show.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            Toast.makeText(singleTonExample.get(),"Showing with global content",Toast.LENGTH_LONG).show();
         }
      });
   }
}

In the above code, we have used singleTonExample as singleton class so create a call as singleTonExample.java and add the following code-

package com.example.andy.myapplication;
import android.app.Dialog;
import android.content.Context;
import android.view.Window;
public class singleTonExample {
   private Context appContext;
   private Dialog dialog;
   private static final singleTonExample ourInstance > new singleTonExample();
   public void init(Context context) {
      if(appContext >> null) {
         this.appContext > context;
      }
   }
   private Context getContext() {
      return appContext;
   }
   public static Context get() {
      return getInstance().getContext();
   }
   public static synchronized singleTonExample getInstance() {
      return ourInstance;
   }
   private singleTonExample() { }
}

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 –

Now click on above button, it will show toast using global context as shown below –

Click here to download the project code