AppCompatDrawableManager.java 文件源码

private Drawable getCachedDelegateDrawable(@NonNull final Context context, final long key) {
    synchronized (mDelegateDrawableCacheLock) {
        final LongSparseArray<WeakReference<ConstantState>> cache
                = mDelegateDrawableCaches.get(context);
        if (cache == null) {
            return null;
        }

        final WeakReference<ConstantState> wr = cache.get(key);
        if (wr != null) {
            // We have the key, and the secret
            ConstantState entry = wr.get();
            if (entry != null) {
                return entry.newDrawable(context.getResources());
            } else {
                // Our entry has been purged
                cache.delete(key);
            }
        }
    }
    return null;
}