Button Click Listener

Implement Click Listener for your Button

In this tutorial we are implementing click listener for two buttons.

File: res/layout/main.xml

<RelativeLayout 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" >

    <TextView
        android:id="@+id/txt_head"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:text="@string/text_value"
        android:textSize="20sp"
        android:padding="20dp"
        android:textColor="#7B68EE" />

    <Button
        android:id="@+id/btnCancel"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/btnOK"
        android:layout_alignBottom="@+id/btnOK"
        android:layout_alignRight="@+id/txt_head"
        android:layout_marginRight="58dp"
        android:text="Cancel" />

    <Button
        android:id="@+id/btnOK"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/txt_head"
        android:layout_toLeftOf="@+id/btnCancel"
        android:text="OK" />


</RelativeLayout>

1. Separate listeners for two buttons

In this case we will assign separate listeners for two different buttons, and we will have to define the response of that button click.

File: src/MainActivity.java

package com.example.eventlistener;

import android.os.Bundle;

import android.app.Activity;

import android.view.Menu;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class MainActivity extends Activity {

private Button btn_Ok,btn_Cancel;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btn_Ok = (Button)findViewById(R.id.btnOK);

btn_Cancel = (Button)findViewById(R.id.btnCancel);

btn_Ok.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub 

Toast.makeText(getApplicationContext(), "OK button was Click", Toast.LENGTH_LONG).show();

}

});

btn_Cancel.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

Toast.makeText(getApplicationContext(), "Cancel button was Click", Toast.LENGTH_LONG).show();

}

});

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.activity_main, menu);

return true;

}

}

2. One listener for two buttons

In this we will assign one listener to multiple buttons, and we will have to define inside the listener which button has been clicked.

File: src/MainActivity.java

package com.example.eventlistener;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class MainActivity extends Activity {

private Button btn_Ok, btn_Cancel;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btn_Ok = (Button) findViewById(R.id.btnOK);

btn_Cancel = (Button) findViewById(R.id.btnCancel);

// create a listener

OnClickListener oclBtn = new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

switch (v.getId()) {

        case R.id.btnOK:

          // OK button

          Toast.makeText(getApplicationContext(), "OK was clicked", Toast.LENGTH_LONG).show();

          break;

        case R.id.btnCancel:

          // Cancel button

         Toast.makeText(getApplicationContext(), "Cancel was clicked", Toast.LENGTH_LONG).show();

          break;

        }

}

};

btn_Ok.setOnClickListener(oclBtn);

btn_Cancel.setOnClickListener(oclBtn);

}

}

The difference in implementation between this and previous code is that now we have created one listener-object for both buttons, but on previous case - we had two listener objects, one for each button. There is a rule - the less objects you create the better, as memory is allocated for each object and it is a quite limited resource, especially for mobile devices. 

There is one more way of creating a listener, which does not require creating an object. We will use an object that is already created - Activity.

Activity as a listener

Here we are making an Activity implementing View.OnClickListener interface and fill its onCreate method.

File: src/MainActivity.java

package com.example.eventlistener;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class MainActivity extends Activity implements OnClickListener {

private Button btn_Ok, btn_Cancel;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btn_Ok = (Button) findViewById(R.id.btnOK);

btn_Cancel = (Button) findViewById(R.id.btnCancel);

btn_Ok.setOnClickListener(this);

btn_Cancel.setOnClickListener(this);

}

@Override

public void onClick(View v) {

// define the button that invoked the listener by id

switch (v.getId()) {

case R.id.btnOK:

// OK button

Toast.makeText(getApplicationContext(), "OK was clicked",

Toast.LENGTH_LONG).show();

break;

case R.id.btnCancel:

// Cancel button

Toast.makeText(getApplicationContext(), "Cancel was clicked",

Toast.LENGTH_LONG).show();

break;

}

}

}