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How to use singleton class 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 demonstrate about How to use singleton class 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"> <EditText android:id = "@+id/editText" android:layout_width = "match_parent" android:layout_height = "wrap_content" android:hint = "Enter text" /> <Button android:id = "@+id/save" android:text = "save in singleTone" android:layout_width = "wrap_content" android:layout_height = "wrap_content" /> </LinearLayout>
In the above code, we have taken edit Ext and button. When user click on a button, it will take data from edit text and store in a singleton class and display value from singleton class in a toast.
Step 3 − Add the following code to src/MainActivity.java
package com.example.andy.myapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
EditText editText;
Button save;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText = findViewById(R.id.editText);
save = findViewById(R.id.save);
save.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(editText.getText().toString().isEmpty()) {
editText.setError("Enter text");
}else{
String editValue = editText.getText().toString();
singleTonExample singletonexample = com.example.andy.myapplication.singleTonExample.getInstance();
singletonexample.setText(editValue);
Toast.makeText(MainActivity.this,singletonexample.getText(),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 java.security.Identity;
public class singleTonExample {
String editValue;
private static final singleTonExample ourInstance = new singleTonExample();
public static singleTonExample getInstance() {
return ourInstance;
}
private singleTonExample() { }
public void setText(String editValue) {
this.editValue = editValue;
}
public String getText() {
return editValue;
}
}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, we have written as tutorialspoint.com” now click on the button it will take data from singleton class and show in the toast as shown below –
Click here to download the project code
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