Animation

Finally, let’s do the animation! We need images of a CS student and the grim reaper. To speed things up, here are some ready-made images in the right dimensions. As you see, there’s a very specific folder structure here, telling Android Studio which images are for which display DPI (“display pixels per inch”). Again, Android Studio takes care of much of this for you, and quasi-official tools like Android Asset Studio handle just about everything else.

  1. Download and unzip the folder into yourpojectlocation/app/src/main.
    The res folder in the zip file will be merged with the res folder already there, so you should end up with only one folder named res.
  2. Put an ImageView into our activity_main.xml layout. Make it display the computer worker guy (the srcCompat attribute selects image, use the button to get a dialog where you can pick images from res). Give the ImageView an ID, let’s say userImageView.
    • Note: Seems to be a bug in Android Studio making it fail to pick up the images you added. If this happens to you, File → Restart →  “Invalidate caches and restart” seems to solve it. You can also switch to Text mode and enter the image reference manually, see LF.
  3. Add constraints at the top of the screen, the top of our “X days left” text, and the right-hand edge of the screen.
  4. Put another ImageView into our layout. This time, select the grim reaper image. Give it an ID too, let’s say reaperImageView.
  5. Add constraints: connect the top of this image to the top of the other image, bottom to bottom, and right-side to right-side. This will make the images end up on top of each other.
  6. Use the Margin tool at the top of the Attributes panel to set the right-hand-side margin of the reaper image to 54dp.
    Note: there seems to be a bug when setting non-standard margins. If you can’t set a margin of 54, set it to one of the values from the dropdown and switch to Text view (button at bottom of designer) to update the margin to 54dp.

If you run the app now, the layout should display the reaper standing almost on top of our poor computer guy. This is the “end” of our animation. What we’ll do next, is to throw the reaper offscreen on app startup, and display an animation moving the reaper towards the user. Of course, the more hours until the deadline, the farther away the reaper should stop!

  1. Create a field for our ImageView reaperImageView and populate it using findViewById like we did earlier.
  2. In onCreate, place the reaper outside the left side of the screen by setting its translationX to a large negative value (-1000 works).
    F or more serious work you should measure how far it is to the end of the screen and how wide the view is, instead of making stupid assumptions like this.
  3. At the end of our updateUI method, we want to start the animation. In Android, the easiest way to animate a view  is to call its animate() method. Try animating the translationX to -10 * number of hours left, and set the duration to something like three seconds. Bonus points for fancier animation!

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LF