The First Android App----Starting Another Activity

To respond to the button's on-click event, open the activity_main.xml layout file and add the android:onClick attribute to the <Button> element:

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send"
    android:onClick="sendMessage"/>
The android:onClick attribute’s value, "sendMessage", is the name of a method in your activity that the system calls when the user clicks the button.

Open the MainActivity class (located in the project's src/ directory) and add the corresponding method:

/** Called when the user clicks the Send button */
publicvoid sendMessage(View view){
    // Do something in response to button
}

This requires that you import the View class:

import android.view.View;

Tip: In Eclipse, press Ctrl + Shift + O to import missing classes (Cmd + Shift + O on Mac).

In order for the system to match this method to the method name given to android:onClick, the signature must be exactly as shown. Specifically, the method must:

• Be public
• Have a void return value
• Have a View as the only parameter (this will be the View that was clicked)

Next, you’ll fill in this method to read the contents of the text field and deliver that text to another activity.