How To Implement Callback Method

This example shows how to implement callback method in android.

Algorithm:

1.) Create a new project by File-> New -> Android Project name it CallbackImplementation.

2.) Create and write following into scr/SubClass.java:

package com.example.callbackimplementation;

public class SubClass {

interface MyCallbackClass{
void callbackReturn();
}

MyCallbackClass myCallbackClass;

void registerCallback(MyCallbackClass callbackClass){
myCallbackClass = callbackClass;
}

void doSomething(){
//do something here

//call callback method
myCallbackClass.callbackReturn();
}

}

3.) Write following into main.xml:

<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"
tools:context=".MainActivity" >

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
<Button
android:id="@+id/callsubclass"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Call sub-class" />
<TextView
android:id="@+id/result"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

</LinearLayout>

4.) Run for output.

Steps:

1.) Create a project named CallbackImplementation and set the information as stated in the image.

Build Target: Android 4.4
Application Name: CallbackImplementation
Package Name: com.example.CallbackImplementation
Activity Name: CallbackImplementationActivity

2.) Open CallbackImplementationActivity.java file and write following code there:

package com.example.callbackimplementation;

import com.example.callbackimplementation.SubClass.MyCallbackClass;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class CallbackImplementationActivity extends Activity implements MyCallbackClass{

Button buttonCallSubClass;
TextView textResult;
SubClass mySubClass;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
buttonCallSubClass = (Button)findViewById(R.id.callsubclass);
textResult = (TextView)findViewById(R.id.result);

mySubClass = new SubClass();

mySubClass.registerCallback(this);

buttonCallSubClass.setOnClickListener(new OnClickListener(){

@Override
public void onClick(View arg0) {
mySubClass.doSomething();
}});
}

@Override
public void callbackReturn() {
textResult.setText("Callback function called");
}

}

3.) Compile and build the project.

Output