Staring Another Activity

In this section, I'll start another Activity when I click the the Send button in Main Activity.

Let's see the following.

1. Respond to the Send Button.

==== activity_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="horizontal"
   >
 <EditText 
     android:id="@+id/message"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:hint="Enter a message"
     android:layout_weight="1"
     />
 <Button 
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:text="Send"
     android:textSize="20sp"
     android:onClick="sendMessage"
     />
</LinearLayout>

: the android:onClick attribute's value, "sendMessage" is the name of a method in MainActivity that the system calls when the user click the button.

2. Build an Intent

==== MainActivity.java ====

public void sendMessage(View view)
 {
  Intent intent = new Intent(getBaseContext(), DisplayMessageActivity.class);
  
  editText = (EditText)findViewById(R.id.message);
  String message = editText.getText().toString();
  
  intent.putExtra(EXTRA_MESSAGE, message);
  startActivity(intent); 

 }

- Add the corresponding method in the MainActivity.

- Inside the sendMessage method, create an Intent to start an activity called DisplaymessageActivity.

3. Create the second Activity

==== DisplayMessageActivity.java ====

protected void onCreate(Bundle savedInstanceState) {

  super.onCreate(savedInstanceState);
  
  // Get the message from the Intent  
  Intent intent = getIntent();
  String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
  
  TextView textView = new TextView(this);
  textView.setTextSize(40);
  textView.setText(message);
 
 // Set the Textview as an activity layout
  setContentView(textView);
}

- We can now run the app.

- When it opens, type a message in the textfield, click the button, and the message in the textfield appears on the second activity.