At the end of each "Hour" in the
Sam's Teach Yourself Android Application Development in 24 Hours
book, there are exercises. We originally designed these exercises to be items people could try to extend their knowledge above and beyond what was learned verbatim in the chapter, given some hints and practice using the the Android documentation that is critical to become familiar with.
Here we present one such exercise that occurs in one of the first real coding hours and present our thought process for determining the solution. Hopefully this will help readers who may be struggling with the difficulty of the exercises. That said, we have also determined, based upon reader feedback, that a handful of exercises in the book are perhaps unfairly difficult. For the next edition of the book, many of these will be replaced or labelled as challenge exercises.
Walk-Through of an ExerciseThis is from Hour 7 on page 125, if you'd like to follow along. As it's the end of the chapter, you already would have downloaded the code to work along with in the chapter. If not, it's available
right here.
"Exercise #1: Modify the LayoutAnimationController in the QuizSplashActivity class to apply animations of each child view within a TableRow control in random order by using the setOrder() method with a value of 2 (random)."
Key Phrase #1: "
Modify the LayoutAnimationController in the QuizSplashActivity"
Thought Process, Step 1: This tells me we're dealing with something to do with the LayoutAnimationController. Luckily, we just covered that on page 122, where we gave this following code:
Animation spinin = AnimationUtils.loadAnimation(this, R.anim.custom_anim);
LayoutAnimationController controller = new LayoutAnimationController(spinin);
TableLayout table = (TableLayout) findViewById(R.id.TableLayout01);
for (int i = 0; i < table.getChildCount(); i++) {
TableRow row = (TableRow) table.getChildAt(i);
row.setLayoutAnimation(controller);
}
Thought Process, Step 2: The code goes in QuizSplashActivity. Since I'm in Hour 7, I've been implementing this activity for the Splash Screen for most of the chapter.
Key Phrase #2: "
to apply animations of each child view within a TableRow control"
Thought Process, Step 3: So far so good. The code is already doing that. We found the code in the section labelled, "Animating All Views in a Layout."
Key Phrase #3: "
in random order"
Thought Process, Step 4: Hmm, I don't know how to do that. Let me read on, finishing the sentence...
Key Phrase #4: "
using the setOrder() method with a value of 2 (random)."
Thought Process, Step 5: Oh, that's how! OK, hold on. I have two options: I could look up this method in the Android SDK docs, or just write it based on what was said in the exercise and see what happens. (Note: We prefer you look it up, like a good student, but experimentation doesn't hurt anything, either.) But perhaps we're lazy so... Let me just add that one line of code to the end of the initial listing, which will now look like:
Animation spinin = AnimationUtils.loadAnimation(this, R.anim.custom_anim);
LayoutAnimationController controller = new LayoutAnimationController(spinin);
TableLayout table = (TableLayout) findViewById(R.id.TableLayout01);
for (int i = 0; i < table.getChildCount(); i++) {
TableRow row = (TableRow) table.getChildAt(i);
row.setLayoutAnimation(controller);
}
controller.setOrder(2); // THIS IS THE ONE NEW LINE OF CODE, THE SOLUTION TO EXERCISE #1
Run the app and see what happens.... Hey! That's pretty neat. Each time I run it, the animations happen in a different order and sometimes some of them happen at the same time.
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