When you complete the previous lesson, you have an app that shows
an activity that consists of a single screen with a text field and a Send button. In this
lesson, you add some code to the MainActivity
that starts a new activity to display a
message when the user taps the Send button.
Respond to the Send button
Follow these steps to add a method to the MainActivity
class that's called when the
Send button is tapped:
In the file app > java > com.example.myfirstapp > MainActivity, add the following
sendMessage()
method stub:Kotlin
class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) } /** Called when the user taps the Send button */ fun sendMessage(view: View) { // Do something in response to button } }
Java
public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } /** Called when the user taps the Send button */ public void sendMessage(View view) { // Do something in response to button } }
You might see an error because Android Studio cannot resolve the
View
class used as the method argument. To clear the error, click theView
declaration, place your cursor on it, and then press Alt+Enter, or Option+Enter on a Mac, to perform a Quick Fix. If a menu appears, select Import class.- Return to the activity_main.xml file to call the method from the button:
- Select the button in the Layout Editor.
- In the Attributes window, locate the onClick property and select sendMessage [MainActivity] from its drop-down list.
Now when the button is tapped, the system calls the
sendMessage()
method.Take note of the details in this method. They're required for the system to recognize the method as compatible with the
android:onClick
attribute. Specifically, the method has the following characteristics: - Next, fill in this method to read the contents of the text field and deliver that text to another activity.
Build an intent
An Intent
is an object that
provides runtime binding between separate components, such as two activities. The
Intent
represents an app’s
intent to do something. You can use intents for a wide variety of tasks, but in this lesson, your
intent starts another activity.
In MainActivity
, add the EXTRA_MESSAGE
constant and the
sendMessage()
code, as shown:
Kotlin
const val EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE" class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) } /** Called when the user taps the Send button */ fun sendMessage(view: View) { val editText = findViewById<EditText>(R.id.editTextTextPersonName) val message = editText.text.toString() val intent = Intent(this, DisplayMessageActivity::class.java).apply { putExtra(EXTRA_MESSAGE, message) } startActivity(intent) } }
Java
public class MainActivity extends AppCompatActivity { public static final String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } /** Called when the user taps the Send button */ public void sendMessage(View view) { Intent intent = new Intent(this, DisplayMessageActivity.class); EditText editText = (EditText) findViewById(R.id.editTextTextPersonName); String message = editText.getText().toString(); intent.putExtra(EXTRA_MESSAGE, message); startActivity(intent); } }
Expect Android Studio to encounter Cannot resolve symbol errors again. To clear the errors, press Alt+Enter, or Option+Return on a Mac. You should end up with the following imports:
Kotlin
import androidx.appcompat.app.AppCompatActivity import android.content.Intent import android.os.Bundle import android.view.View import android.widget.EditText
Java
import androidx.appcompat.app.AppCompatActivity; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.widget.EditText;
An error still remains for DisplayMessageActivity
, but that's okay. You fix it in
the next section.
Here's what's going on in sendMessage()
:
The
Intent
constructor takes two parameters, aContext
and aClass
.The
Context
parameter is used first because theActivity
class is a subclass ofContext
.The
Class
parameter of the app component, to which the system delivers theIntent,
is, in this case, the activity to start.The
putExtra()
method adds the value ofEditText
to the intent. AnIntent
can carry data types as key-value pairs called extras.Your key is a public constant
EXTRA_MESSAGE
because the next activity uses the key to retrieve the text value. It's a good practice to define keys for intent extras with your app's package name as a prefix. This ensures that the keys are unique, in case your app interacts with other apps.- The
startActivity()
method starts an instance of theDisplayMessageActivity
that's specified by theIntent
. Next, you need to create that class.
Create the second activity
To create the second activity, follow these steps:
- In the Project window, right-click the app folder and select New > Activity > Empty Activity.
- In the Configure Activity window, enter "DisplayMessageActivity" for Activity Name. Leave all other properties set to their defaults and click Finish.
Android Studio automatically does three things:
- Creates the
DisplayMessageActivity
file. - Creates the layout file
activity_display_message.xml
, which corresponds with theDisplayMessageActivity
file. - Adds the required
<activity>
element inAndroidManifest.xml
.
If you run the app and tap the button on the first activity, the second activity starts but is empty. This is because the second activity uses the empty layout provided by the template.
Add a text view

The new activity includes a blank layout file. Follow these steps to add a text view to where the message appears:
- Open the file app > res > layout > activity_display_message.xml.
- Click Enable Autoconnection to Parent
in the toolbar. This enables Autoconnect. See figure 1.
- In the Palette panel, click Text, drag a TextView into the layout, and drop it near the top-center of the layout so that it snaps to the vertical line that appears. Autoconnect adds left and right constraints in order to place the view in the horizontal center.
- Create one more constraint from the top of the text view to the top of the layout, so that it appears as shown in figure 1.
Optionally, you can make some adjustments to the text style if you expand textAppearance in the Common Attributes panel of the Attributes window, and change attributes such as textSize and textColor.
Display the message
In this step, you modify the second activity to display the message that was passed by the first activity.
In
DisplayMessageActivity
, add the following code to theonCreate()
method:Kotlin
override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_display_message) // Get the Intent that started this activity and extract the string val message = intent.getStringExtra(EXTRA_MESSAGE) // Capture the layout's TextView and set the string as its text val textView = findViewById<TextView>(R.id.textView).apply { text = message } }
Java
@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_display_message); // Get the Intent that started this activity and extract the string Intent intent = getIntent(); String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE); // Capture the layout's TextView and set the string as its text TextView textView = findViewById(R.id.textView); textView.setText(message); }
Press Alt+Enter, or Option+Return on a Mac, to import these other needed classes:
Kotlin
import androidx.appcompat.app.AppCompatActivity import android.content.Intent import android.os.Bundle import android.widget.TextView
Java
import androidx.appcompat.app.AppCompatActivity; import android.content.Intent; import android.os.Bundle; import android.widget.TextView;
Add upward navigation
Each screen in your app that's not the main entry point, which are all the screens that aren't the home screen, must provide navigation that directs the user to the logical parent screen in the app's hierarchy. To do this, add an Up button in the app bar.
To add an Up button, you need to declare which activity is the logical parent in the
AndroidManifest.xml
file.
Open the file at app > manifests > AndroidManifest.xml, locate the
<activity>
tag for DisplayMessageActivity
, and replace it with the
following:
<activity android:name=".DisplayMessageActivity" android:parentActivityName=".MainActivity"> <!-- The meta-data tag is required if you support API level 15 and lower --> <meta-data android:name="android.support.PARENT_ACTIVITY" android:value=".MainActivity" /> </activity>
The Android system now automatically adds the Up button to the app bar.
Run the app
Click Apply Changes
in the
toolbar to run the app. When it opens, type a message in the text field and tap
Send to see the message appear in the second activity.

That's it, you've built your first Android app!
To continue to learn the basics about Android app development, go back to Build your first app and follow the other links provided there.