Navigation Among Activities Using Android Studio 1.0

• change Relative Layout with Linear Layout
• Add a Text Field
• Add String resource
• Add a button and its listener as well

String.xml

String.xml contains the string resources such as "app name" , "edit_message" , "action settings" and so on. So we must remove the default string "hello world". It is just an activity with a Text Field with a Button. Now just try to attach a listener of the button so that the message can be sent and another activity will receive that message.

XML Design

The previous code produces the following output: Building an Intent

After creation of the first activity with a TextField and a Button as explained above it is now time to initiate this activity using a thing called an Intent. An Intent is an object that provides runtime binding between two separate components (such as two activities). The Intent represents an application's "intent to do something". Intents could be used for a wide variety of tasks, but most often they are used to start another activity. In MainActivity.java declare a method named sendMessage(View view) with these parameters and inside it create an Intent to start an activity called DisplayMessageActivity with this code given below:

• We need to create a class for ChildActivity because the reference to this class might raise an error in Android Studio.
  
• Note that in the constructor used here, "this" is used because the Activity is a subclass of the Context class and imports the Intent class. ( import navigation-among-activities-using-android-studio.content.Intent; ).

  However, Android Studio automatically suggests that we press ALT+ENTER and the relevant class will be imported and the packages as well.
• Inside the sendMessage() method use findViewById() to get an EditText element.

  1. EditText editText = (EditText) findViewById(R.id.edit_message);
     
• At the top of the file import the EditText class again. Press ALT+ENTER and the relevant class will be imported and the packages as well.
  
• Assign the text to a local message variable and use the putExtra() method as in the following:
  

  1. String message = editText.getText().toString();
  2. intent.putExtra(EXTRA_MESSAGE, message);
  3. }
     
• We must add an EXTRA_MESSAGE definition as shown below:

  1. public class MyActivity extends ActionBarActivity {
  2. public final static String EXTRA_MESSAGE = "com.example..megatron.MESSAGE";
  4. }
     
• Finally just finish the sendMessage() method with startActivity(intent) and now invoke the send button.

Create a second activity

• Go to the Java directory on the package name com.example.gkumar.megatron. Right-click it and select new > Activity > Blank Activity.

• In the naming window of Activity choose Activity name as ChildActivity
• layout Name : activity_child.xml
• Title: ChildActivity
• Hierarchical parent: MainActivity
• package name: com.example.gkumar.megatron

• The newly created Activity file must have an implementation of onCreate() and onOptionsItemSelected(), that handles the action bar's up behavior and must remain untouched.
• Remove the onCreateOptionsMenu() method, we don't need it.

• Look at the default method generated by setContentView(R.layout.activity_display_message). Remove that line.
• Get the intent and assign it to a local variable.

  1. Intent intent = getIntent();
     
• At the top import the Intent class as we did in MainActivity.java.
• Now receive the message delivered by the previous activity using the getStringExtra() method.

  1. String message = intent.getStringExtra(MyActivity.EXTRA_MESSAGE);
     

• in the onCreate() method create a TextView object
• set the text size and message with setText();
• set the text size up to 50 and the text as a message.
• add the TextView as a root view of the activity's layout by ing it to setContentView(textview);