Button View in Android

Button, as understood by its name, is a component which can be pressed or clicked by the user to perform an action. It has the same properties as a TextView, with a few Button specific properties.

Below we have specified how to define a button view in your android application using the layout XML:

<Button
    android:id="@+id/btn_submit"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Submit"
    android:textColor="@android:color/holo_blue_dark"
    />

The main usage of the Button view is that whenever we click a button, we can set a method that will handle that specific button request and will carry out the necessary action. This can be done inside the Activity class as following:

Note: If you do not know about the Activity class as of now, do not worry. We will explain it very soon.

public class MainActivity extends Activity {
	@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        // creating instance of button
        Button b = (Button) findViewById(R.id.btn_submit);
        // setting on click event listener
        b.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
             
                // Perform action on click
                 
            }
        });
    }
}

Therefore, whenever we press the button with id btn_submit, the above method is called which executes the code inside it.

Using android:onClick to add behaviour to Button

We can also assign a method directly in the layout XML while defining the button using, android:onClick attribute, like specified below.

<Button
    android:id="@+id/btn_submit"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Submit"
    android:textColor="@android:color/holo_blue_dark"
    android:onClick="study"
    />

When user will click on the Button defined in the above layout xml file, then Android system will call study(View) method, defined in MainActivity.java file. In order for this to work, the method must be public and accept a View type as its only parameter.

public void study(View view) {

    //Perform action on click
    
}

Similarly, the android:onClick attribute can be used with all the available View subclasses, like TextView, EditText, RadioButton, CheckBox etc.

Output Screen

Commonly used attributes for Button

Here are some commonly used attributes for styling the Button View

• android:gravity: This can be used to set the position of any View on the app screen. The available value are right, left, center, center_vertical etc. You can also use to values together, using the | symbol.
• android:textSize: To set text size inside button.
• android:background: To set the background color of the button.
• Picture can be added to the button, alongside the text by using android:drawableRight, android:drawableLeft, android:drawableTop and android:drawableBottom, respectively.: