Android Studio for beginners

Android Studio for beginners, Part 2: Explore and code the app

Use Android Studio's project editor to write your first animated Android app

Page 2 of 2

Exploring and coding strings.xml

W2A relies on strings.xml to store string data that is referenced from other locations. Refer back to Listing 2 and you'll notice that the <Button> tag includes an android:text="@string/animate" attribute. This attribute references the button's text via @string/animate, which references a string resource named animate that's stored in strings.xml. Listing 3 presents this file's contents.

Listing 3. strings.xml

<?xml version="1.0" encoding="utf-8"?>
   <string name="app_name">W2A</string>
   <string name="animate">Animate</string>

As well as animate, Listing 3 reveals a string resource identified as app_name. This resource ID identifies the app's name and is referenced from the app's AndroidManifest.xml file, typically from the label attribute of the application element start tag.

Save strings.xml

In your project window, the values sub-branch of the res sub-branch includes a strings.xml sub-branch. Double-click this sub-branch to show the strings.xml tab, then replace its contents with Listing 3 and save the changes.

Exploring and coding animate.xml

Finally, W2A relies on android_animate.xml, which stores an animation list of drawable items. Listing 4 presents the contents of this file.

Listing 4. android_animate.xml

<animation-list xmlns:android=""
   <item android:drawable="@drawable/android0" android:duration="500" />
   <item android:drawable="@drawable/android1" android:duration="500" />
   <item android:drawable="@drawable/android2" android:duration="500" />
   <item android:drawable="@drawable/android0" android:duration="500" />

Listing 4 starts with an animation-list element that describes the drawable sequence. This element's oneshot attribute determines if the animation will cycle in a loop (when this attribute is assigned "false") or occur only once (when it's assigned "true"). When "true" is assigned to oneshot, you must invoke AnimationDrawable()'s stop() method before its start() method to generate another oneshot animation sequence.

Nested inside the animation-list element is a sequence of item elements. Each item element identifies one drawable in the animation sequence via its drawable attribute. The @drawable/androidx resource reference (where x ranges from 0 through 2) identifies an image file whose name starts with android. The duration attribute identifies the number of milliseconds that must elapse before the next item element's drawable is displayed.

Save animate.xml

In the project window, right-click the drawable sub-branch of the res sub-branch. Figure 3 shows the resulting pop-up menu.

androidstudiop2 fig3

Figure 3. Add android_animate.xml as a new drawable resource

Select New from the pop-up menu, followed by File. Figure 4 shows the resulting New File dialog box.

androidstudiop2 fig4

Figure 4. Enter android_animate.xml

Type android_animate.xml into the "Enter a new file name" text field and click OK. (You'll see an android_animate.xml sub-branch under the drawable sub-branch.) Then, replace the contents of the resulting android_animate.xml tab with the code from Listing 4 and save your changes.

You'll also need to copy the android0.png, android1.png, and android2.png files (referenced in Listing 4) from the code source associated with this article to the drawable branch. Assuming you're working in Windows, select these files from Windows Explorer and paste them into this branch (right-click the branch name and select Paste).

Conclusion to Part 2

Now that you understand W2A's architecture and have learned how to code a simple animated mobile app in Android Studio, you're ready to build and run your app. Turn to Part 3 when you're ready for this final step.

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