src/android/src/com/google/android/inputmethod/japanese/view/DrawableCache.java

// Copyright 2010-2014, Google Inc.
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package org.mozc.android.inputmethod.japanese.view;

import com.google.common.base.Optional;
import com.google.common.base.Preconditions;

import android.content.res.Resources;
import android.graphics.drawable.Drawable;
import android.util.SparseArray;

/**
 * Cache of android's Drawable instances.
 *
 */
public class DrawableCache {

  private final SparseArray<Drawable> cacheMap = new SparseArray<Drawable>(128);
  private Skin skin = Skin.getFallbackInstance();
  private final Resources resources;

  public DrawableCache(Resources resources) {
    this.resources = Preconditions.checkNotNull(resources);
  }

  public void setSkin(Skin skin) {
    Preconditions.checkNotNull(skin);
    if (this.skin.equals(skin)) {
      return;
    }

    this.skin = skin;
    cacheMap.clear();
  }

  /**
   * First, looks up cache data in this instance, and returns the value if found.
   * If not found, tries to load {@code Drawable} instance from resources given via the constructor,
   * stores it into this instance, and returns it.
   */
  public Optional<Drawable> getDrawable(int resourceId) {
    if (resourceId == 0) {
      // 0 is invalid resource id.
      return Optional.<Drawable>absent();
    }

    Integer key = Integer.valueOf(resourceId);
    Optional<Drawable> drawable = Optional.fromNullable(cacheMap.get(key));
    if (!drawable.isPresent()) {
      drawable = Optional.of(skin.getDrawable(resources, resourceId));
      cacheMap.put(key, drawable.get());
    }
    return drawable;
  }

  /**
   * Clears all {@code Drawable}s stored in this instance.
   */
  public void clear() {
    cacheMap.clear();
  }
}