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How to use Singleton Alert Dialog in android?
Before getting into example, we should know what singleton design pattern 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 Alert Dialog 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 = "Alert Dialog from 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 alert Dialog from singleton class.
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;
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) {
singletonexample.AlertDialog(MainActivity.this);
}
});
}
}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.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.speech.tts.TextToSpeech;
import android.widget.Toast;
public class singleTonExample {
static TextToSpeech t1;
private static singleTonExample ourInstance = new singleTonExample();
private Context appContext;
private singleTonExample() { }
public static Context get() {
return getInstance().getContext();
}
public static synchronized singleTonExample getInstance() {
return ourInstance;
}
public void init(Context context) {
if (appContext = = null) {
this.appContext = context;
}
}
private Context getContext() {
return appContext;
}
public void AlertDialog(final MainActivity mainActivity) {
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(mainActivity);
alertDialogBuilder.setMessage("Are you sure, You wanted to make decision");
alertDialogBuilder.setPositiveButton("yes",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
Toast.makeText(mainActivity, "You clicked yes button", Toast.LENGTH_LONG).show();
}
});
alertDialogBuilder.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
mainActivity.finish();
}
});
AlertDialog alertDialog = alertDialogBuilder.create();
alertDialog.show();
}
}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 alert dialog from singleton class as shown below -.
Click here to download the project code
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