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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package androidx.contentpager.content;
     18 
     19 import static androidx.core.util.Preconditions.checkArgument;
     20 
     21 import android.app.LoaderManager;
     22 import android.app.LoaderManager.LoaderCallbacks;
     23 import android.content.Context;
     24 import android.content.Loader;
     25 import android.database.Cursor;
     26 import android.os.Bundle;
     27 import android.util.Log;
     28 
     29 import androidx.annotation.NonNull;
     30 
     31 /**
     32  * A {@link ContentPager.QueryRunner} that executes queries using a {@link LoaderManager}.
     33  * Use this when preparing {@link ContentPager} to run in an Activity or Fragment scope.
     34  */
     35 public final class LoaderQueryRunner implements ContentPager.QueryRunner {
     36 
     37     private static final boolean DEBUG = false;
     38     private static final String TAG = "LoaderQueryRunner";
     39     private static final String CONTENT_URI_KEY = "contentUri";
     40 
     41     private final Context mContext;
     42     private final LoaderManager mLoaderMgr;
     43 
     44     public LoaderQueryRunner(@NonNull Context context, @NonNull LoaderManager loaderMgr) {
     45         mContext = context;
     46         mLoaderMgr = loaderMgr;
     47     }
     48 
     49     @Override
     50     @SuppressWarnings("unchecked")  // feels spurious. But can't commit line :80 w/o this.
     51     public void query(final @NonNull Query query, @NonNull final Callback callback) {
     52         if (DEBUG) Log.d(TAG, "Handling query: " + query);
     53 
     54         LoaderCallbacks callbacks = new LoaderCallbacks<Cursor>() {
     55             @Override
     56             public Loader<Cursor> onCreateLoader(final int id, final Bundle args) {
     57                 if (DEBUG) Log.i(TAG, "Loading results for query: " + query);
     58                 checkArgument(id == query.getId(), "Id doesn't match query id.");
     59 
     60                 return new android.content.CursorLoader(mContext) {
     61                     @Override
     62                     public Cursor loadInBackground() {
     63                         return callback.runQueryInBackground(query);
     64                     }
     65                 };
     66             }
     67 
     68             @Override
     69             public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {
     70                 if (DEBUG) Log.i(TAG, "Finished loading: " + query);
     71                 mLoaderMgr.destroyLoader(query.getId());
     72                 callback.onQueryFinished(query, cursor);
     73             }
     74 
     75             @Override
     76             public void onLoaderReset(Loader<Cursor> loader) {
     77                 if (DEBUG) Log.w(TAG, "Ignoring loader reset for query: " + query);
     78             }
     79         };
     80 
     81         mLoaderMgr.restartLoader(query.getId(), null, callbacks);
     82     }
     83 
     84     @Override
     85     public boolean isRunning(@NonNull Query query) {
     86         Loader<Cursor> loader = mLoaderMgr.getLoader(query.getId());
     87         return loader != null && loader.isStarted();
     88         // Hmm, when exactly would the loader not be started? Does it imply that it will
     89         // be starting at some point?
     90     }
     91 
     92     @Override
     93     public void cancel(@NonNull Query query) {
     94         mLoaderMgr.destroyLoader(query.getId());
     95     }
     96 }
     97