How it works...

The real work of this exercise is in the onClickSwitchActivity() method from step 3. This is where we declare the second activity for the Intent using SecondActivity.class. We went one step further by adding the close button to the second activity to show a common real-world situation: launching a new activity, then returning to the original calling activity. This behavior is accomplished in the onClickClose() function. All it does is call finish(), but that tells the OS that we're done with the activity. Finish doesn't actually return us to the calling activity (or any specific activity for that matter); it just closes the current activity and relies on the application's back stack to show the last activity. If we want a specific activity, we can again use the Intent object and specify the activity class name when creating the Intent.

This activity switching does not make a very exciting application. Our activity does nothing but demonstrates how to switch from one activity to another, which of course will form a fundamental aspect of almost any application that we develop.

If we had manually created the activities, we would need to add them to the manifest. Using the New Android Activity wizard will automatically add the necessary elements to the Android Manifest file. To see what Android Studio did for you, open the AndroidManifest.xml file and look at the <application> element:

<activity android:name=".MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>
<activity android:name=".SecondActivity"></activity>

One thing to note in the preceding auto-generated code is that the second activity does not have the <intent-filter> element. The main activity is generally the entry point when starting the application. That's why MAIN and LAUNCHER are defined so that the system will know which activity to launch when the application starts.