CH 21 Speed Control Challenge with data binding

Android Programming (3rd Edition) 21. Unit Testing and Audio Playback
1

I had some trouble with data binding giving me all sorts of errors. I’m glad I persisted because it is helping me learn how data binding works, though perhaps not best practices. Feedback welcome!!! Here’s my solution:

BeatBox.java

  • add mPlaybackSpeed and constants to keep track of minimum and maximum speeds

  • add getters and setters; Not sure if overly cautious, but I included a check to enforce the minimum and maximum values getting passed into the setter

    public class BeatBox {

      public static final float MIN_PLAYBACK_SPEED = 0.5f;
  public static final float MAX_PLAYBACK_SPEED = 2.0f;

  private static final String TAG = "BeatBox";

  private static final String SOUNDS_FOLDER = "sample_sounds";
  private static final int MAX_SOUNDS = 5;

  private final AssetManager mAssets;
  private final List<Sound> mSounds = new ArrayList<>();
  private SoundPool mSoundPool;
  private float mPlaybackSpeed;

  public BeatBox(Context context) {
      mAssets = context.getAssets();
      mSoundPool = new SoundPool(MAX_SOUNDS, AudioManager.STREAM_MUSIC, 0);
      mPlaybackSpeed = 1.0f;
      loadSounds();
  }

  public void play(Sound sound) {
      Integer soundId = sound.getSoundId();
      if (soundId == null) {
          return;
      }
      mSoundPool.play(soundId, 1.0f, 1.0f, 1, 0, mPlaybackSpeed);
  }

  public void release() {
      mSoundPool.release();
  }

  private void loadSounds() {
      String[] soundNames;
      try {
          soundNames = mAssets.list(SOUNDS_FOLDER);
          Log.i(TAG, "Found " + soundNames.length + " sounds");
      } catch (IOException ioe) {
          Log.e(TAG, "Could not list assets", ioe);
          return;
      }

      for (String filename : soundNames) {
          try {
              String assetPath = SOUNDS_FOLDER + "/" + filename;
              Sound sound = new Sound(assetPath);
              load(sound);
              mSounds.add(sound);
          } catch (IOException ioe) {
              Log.e(TAG, "Could not load sound " + filename, ioe);
          }
      }
  }

  private void load(Sound sound) throws IOException {
      AssetFileDescriptor afd = mAssets.openFd((sound.getAssetPath()));
      int soundId = mSoundPool.load(afd, 1);
      sound.setSoundId(soundId);
  }

  public List<Sound> getSounds() {
      return Collections.unmodifiableList(mSounds);
  }

  public float getPlaybackSpeed() {
      return mPlaybackSpeed;
  }

  public void setPlaybackSpeed(float playbackSpeed) {
      if (playbackSpeed > MAX_PLAYBACK_SPEED) {
          mPlaybackSpeed = MAX_PLAYBACK_SPEED;
      } else if (playbackSpeed < MIN_PLAYBACK_SPEED) {
          mPlaybackSpeed = MIN_PLAYBACK_SPEED;
      } else {
          mPlaybackSpeed = playbackSpeed;
      }

  }

    }

SpeedSeekBarAdapter.java

  • add this class to handle the flow between my BeatBox model and my view since they use different min/max/range/types

  • add a method with the same number and type of arguments as SeekBarBindingAdapter.onProgressChanged as listener for moving the slider

  • I’m not entirely sure why I didn’t have to use @Bindable anywhere…

    public class SpeedSeekBarAdapter extends BaseObservable {

      private BeatBox mBeatBox;

  private int mMinSeekBar;
  private int mMaxSeekBar;
  private int mRangeSeekBar;
  private float mMinSpeed;
  private float mMaxSpeed;
  private float mRangeSpeed;

  public SpeedSeekBarAdapter(BeatBox beatBox, SeekBar seekBar) {
      mBeatBox = beatBox;
      mMinSeekBar = 0;
      mMaxSeekBar = seekBar.getMax();
      mRangeSeekBar = mMaxSeekBar - mMinSeekBar;
      mMinSpeed = BeatBox.MIN_PLAYBACK_SPEED;
      mMaxSpeed = BeatBox.MAX_PLAYBACK_SPEED;
      mRangeSpeed = mMaxSpeed - mMinSpeed;
  }

  public float getSpeed() {
      return mBeatBox.getPlaybackSpeed();
  }

  public int getSeekBarValue() {
      int seekBarValue = Math.round((mBeatBox.getPlaybackSpeed() - mMinSpeed) / mRangeSpeed * mRangeSeekBar + mMinSeekBar);

      if (seekBarValue > mMaxSeekBar) {
          return mMaxSeekBar;
      } else if (seekBarValue < mMinSeekBar) {
          return mMinSeekBar;
      } else {
          return seekBarValue;
      }
  }

  public void setSpeed(int seekBarValue) {
      float speed = ((float) seekBarValue - mMinSeekBar) / mRangeSeekBar * mRangeSpeed + mMinSpeed;
      mBeatBox.setPlaybackSpeed(speed);
      notifyChange();
  }

  public void changeSpeed(SeekBar seekBar, int progress, boolean fromUser) {
      setSpeed(progress);
  }

    }

strings.xml
<resources> <string name="app_name">BeatBox</string> <string name="playback_speed">Playback Speed: %.1f x</string> </resources>

fragment_beat_box.xml

  • add TextView and SeekBar widgets

  • add data tag with reference to my new “adapter” (I don’t know what to call it)

  • call all my previously setup items

    <?xml version="1.0" encoding="utf-8"?> 

      <data>
      <variable
          name="adapter"
          type="com.bignerdranch.android.beatbox.SpeedSeekBarAdapter"/>
  </data>

  <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:orientation="vertical">

      <android.support.v7.widget.RecyclerView
          android:id="@+id/recycler_view"
          android:layout_width="match_parent"
          android:layout_height="0dp"
          android:layout_weight="1"/>

      <TextView
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          tools:text="@string/playback_speed"
          android:text="@{String.format(@string/playback_speed, adapter.getSpeed)}"/>
      <SeekBar
          android:id="@+id/seekBar"
          android:layout_width="match_parent"
          android:layout_height="32dp"
          android:progress="@{adapter.seekBarValue}"
          android:onProgressChanged="@{adapter.changeSpeed}"/>

  </LinearLayout>

BeatBoxFragment.java

  • add binding.setAdapter(new SpeedSeekBarAdapter(mBeatBox, binding.seekBar)); to onCreateView(...)

  • on further review “adapter” was probably not the best choice for a data object variable name here considering binding.recyclerView has a setAdapter(...) too

    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    FragmentBeatBoxBinding binding = DataBindingUtil.inflate(inflater, R.layout.fragment_beat_box, container, false);

      binding.recyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));
  binding.recyclerView.setAdapter(new SoundAdapter(mBeatBox.getSounds()));

  binding.setAdapter(new SpeedSeekBarAdapter(mBeatBox, binding.seekBar));

  return binding.getRoot();

    }

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