「android学習」JavaでDiskLruCache更新を実現するサンプルコード

2015年3月4日

Javaコード:
private DiskLruCache mDiskCache;
private static final int DISK_CACHE_SIZE = 1024 * 1024 * 10; // 10MB
private static final String DISK_CACHE_SUBDIR = “thumbnails";

@Override
protected void onCreate(Bundle savedInstanceState) {
…
// メモリキャッシュを初期化
…
File cacheDir = getCacheDir(this, DISK_CACHE_SUBDIR);
mDiskCache = DiskLruCache.openCache(this, cacheDir, DISK_CACHE_SIZE);
…
}

class BitmapWorkerTask extends AsyncTask {
…
// Decode image in background.
@Override
protected Bitmap doInBackground(Integer… params) {
final String imageKey = String.valueOf(params[0]);

// Check disk cache in background thread
Bitmap bitmap = getBitmapFromDiskCache(imageKey);

if (bitmap == null) { // Not found in disk cache
// Process as normal
final Bitmap bitmap = decodeSampledBitmapFromResource(
getResources(), params[0], 100, 100));
}

// キャッシュへの最終的なビットマップを追加
addBitmapToCache(String.valueOf(imageKey, bitmap);

return bitmap;
}
…
}

public void addBitmapToCache(String key, Bitmap bitmap) {
// Add to memory cache as before
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}

// Also add to disk cache
if (!mDiskCache.containsKey(key)) {
mDiskCache.put(key, bitmap);
}
}

public Bitmap getBitmapFromDiskCache(String key) {
return mDiskCache.get(key);
}

// Creates a unique subdirectory of the designated app cache directory. Tries to use external
// but if not mounted, falls back on internal storage.
public static File getCacheDir(Context context, String uniqueName) {
// Check if media is mounted or storage is built-in, if so, try and use external cache dir
// otherwise use internal cache dir
final String cachePath = Environment.getExternalStorageState() == Environment.MEDIA_MOUNTED
|| !Environment.isExternalStorageRemovable() ?
context.getExternalCacheDir().getPath() : context.getCacheDir().getPath();

return new File(cachePath + File.separator + uniqueName);
}