Many Ways To Assign Click Event To Button On Android

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Ho Ngoc Trang,  trangho214@gmail.com, is the author of this article and she contributes to RobustTechHouse Blog. 

Introduction

We can assign the click event to many different components such as Button, ListView, Dropbox and etc. When a component is assigned a click event, the component will do a specific task whenever it is clicked on. One of the most common components to assign click events to is a Button.

There are many tutorials to assign click events to buttons  but each of them has it’s own way to implement the click event. When I was a beginner Android programmer, I was very confused about which way is the right one, or why Tutorial A is different from Tutorial B when they might be doing the same thing.

In this article, I decided to list the four different ways I know to accomplish this.

1. Apply an onClickListener to the button in your activity

Declaring the OnClickListener within the call to the setOnClickListener method is common. A typical use of a push button in an activity is implemented like the following

main.xml

 <Button
        android:id="@+id/btn1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button1"/>

MainActivity Class

public class MainActivity extends Activity{
    Button button1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //find view-elements
        button1 = (Button)findViewById(R.id.btn1);
        //Apply an instance of OnClickListener directly on  button,
        // When the button is clicked, the listener reacts and runs the code from onClick method.
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //TODO: do something here
                Toast.makeText(MainActivity.this,"Button1 is clicked", Toast.LENGTH_SHORT ).show();
            }
        });
    }

2. Define an onClick method in main.xml

Instead of applying an OnClickListener to the button in your activity, you can assign a method to your button in the XML layout, using the android:onClick attribute. In this attribute we specify the name of the method in Activity. This method will be invoked when the button is clicked.

main.xml

<Button
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="onClickButton2" 
    android:text="Button2"/>

Then, add this method inside Activity (MainActivity.java). Method requirements: public, void and receives a View object as a parameter:

MainActivity Class

public class MainActivity extends Activity{
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
     //The View passed into the method is a reference to the widget that was clicked.
    public void onClickButton2(View v)
    {
        Toast.makeText(this,"Button2 is clicked", Toast.LENGTH_SHORT ).show();
    } 
}

3. Implement View.OnclickListener interface in the Activity

The Activity itself can implement the OnClickListener. Since the Activity object already exists this saves a small amount of memory by not requiring another object to host the onClick method.  To assign click event to button on Android, this frequently seems like the recommended way.

main.xml

<Button
        android:id="@+id/btn3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button3"/>

MainActivity class

public class MainActivity extends Activity implements View.OnClickListener{
    Button button3;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // find View-elements
        button3 = (Button)findViewById(R.id.btn3);
        // assign listener to button
        button3.setOnClickListener(this);
    }

    //Implement onClick method and tell it what to do when clicked.
    @Override
    public void onClick(View v) {
        if(v.getId() == R.id.btn3)
                Toast.makeText(MainActivity.this,"Button3 is clicked", Toast.LENGTH_SHORT ).show();
}

4. Assign a variable of OnClickListener interface type to the button

In this way, we will declare a variable as a type of OnClickListener interface, then assigned it to the button.

main.xml

<Button
     android:id="@+id/btn4"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:text="Button4"/>

MainActivity class

public class MainActivity extends Activity{
    Button button4;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // find View-elements
        button4 = (Button)findViewById(R.id.btn4);
        // assign listener to button
        button4.setOnClickListener(onClickButton4);
    }

  View.OnClickListener onClickButton4 = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Toast.makeText(MainActivity.this,"Button4 is clicked", Toast.LENGTH_LONG ).show();
        }
    };
}

Conclusion

Many roads lead to Rome to assign click event to button on Android. Depending on your code layout, feel free to choose which of the above methods to use.

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