Java tutorial
/* * Copyright (C) 2011 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package cn.tangxb.imageselector; import android.content.ContentResolver; import android.content.Context; import android.database.Cursor; import android.net.Uri; import android.provider.MediaStore; import android.support.v4.content.AsyncTaskLoader; import android.support.v4.content.ContentResolverCompat; import android.support.v4.os.CancellationSignal; import android.support.v4.os.OperationCanceledException; import java.util.ArrayList; import java.util.List; import cn.tangxb.imageselector.model.PhotoModel; /** * Static library support version of the framework's {@link android.content.CursorLoader}. * Used to write apps that run on platforms prior to Android 3.0. When running * on Android 3.0 or above, this implementation is still used; it does not try * to switch to the framework's implementation. See the framework SDK * documentation for a class overview. */ public class PhotoModelTaskLoader extends AsyncTaskLoader<ArrayList<PhotoModel>> { final ForceLoadContentObserver mObserver; Uri mUri; String[] mProjection; String mSelection; String[] mSelectionArgs; String mSortOrder; Cursor mCursor; CancellationSignal mCancellationSignal; ArrayList<PhotoModel> mData; /* Runs on a worker thread */ @Override public ArrayList<PhotoModel> loadInBackground() { synchronized (this) { if (isLoadInBackgroundCanceled()) { throw new OperationCanceledException(); } mCancellationSignal = new CancellationSignal(); } try { Cursor cursor = ContentResolverCompat.query(getContext().getContentResolver(), MediaStore.Images.Media.EXTERNAL_CONTENT_URI, new String[] { MediaStore.Images.ImageColumns.DATA, MediaStore.Images.ImageColumns.DATE_ADDED, MediaStore.Images.ImageColumns.SIZE }, null, null, MediaStore.Images.ImageColumns.DATE_ADDED, mCancellationSignal); if (cursor != null) { try { // Ensure the cursor window is filled. cursor.getCount(); cursor.registerContentObserver(mObserver); mData = new ArrayList<>(); if (cursor == null || !cursor.moveToNext()) return mData; cursor.moveToLast(); do { if (cursor.getLong(cursor.getColumnIndex(MediaStore.Images.ImageColumns.SIZE)) > 1024 * 10) { PhotoModel photoModel = new PhotoModel(); photoModel.setOriginalPath( cursor.getString(cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA))); mData.add(photoModel); } } while (cursor.moveToPrevious()); } catch (RuntimeException ex) { cursor.close(); throw ex; } } return mData; } finally { synchronized (this) { mCancellationSignal = null; } } } @Override public void cancelLoadInBackground() { super.cancelLoadInBackground(); synchronized (this) { if (mCancellationSignal != null) { mCancellationSignal.cancel(); } } } /* Runs on the UI thread */ @Override public void deliverResult(ArrayList<PhotoModel> data) { if (isReset()) { // The Loader has been reset; ignore the result and invalidate the data. releaseResources(data); return; } if (isStarted()) { super.deliverResult(data); } // Hold a reference to the old data so it doesn't get garbage collected. // We must protect it until the new data has been delivered. ArrayList<PhotoModel> oldData = mData; mData = data; // Invalidate the old data as we don't need it any more. if (oldData != null && oldData != data) { releaseResources(oldData); } } /** * Creates an empty unspecified CursorLoader. You must follow this with * calls to {@link #setUri(Uri)}, {@link #setSelection(String)}, etc * to specify the query to perform. */ public PhotoModelTaskLoader(Context context) { super(context); mObserver = new ForceLoadContentObserver(); } /** * Creates a fully-specified CursorLoader. See * {@link ContentResolver#query(Uri, String[], String, String[], String) * ContentResolver.query()} for documentation on the meaning of the * parameters. These will be passed as-is to that call. */ public PhotoModelTaskLoader(Context context, Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { super(context); mObserver = new ForceLoadContentObserver(); mUri = uri; mProjection = projection; mSelection = selection; mSelectionArgs = selectionArgs; mSortOrder = sortOrder; } /** * Starts an asynchronous load of the contacts list data. When the result is ready the callbacks * will be called on the UI thread. If a previous load has been completed and is still valid * the result may be passed to the callbacks immediately. * <p/> * Must be called from the UI thread */ @Override protected void onStartLoading() { if (mData != null) { deliverResult(mData); } if (takeContentChanged() || mCursor == null) { forceLoad(); } } /** * Must be called from the UI thread */ @Override protected void onStopLoading() { // Attempt to cancel the current load task if possible. cancelLoad(); } @Override public void onCanceled(ArrayList<PhotoModel> data) { super.onCanceled(data); releaseResources(data); } @Override protected void onReset() { super.onReset(); // Ensure the loader is stopped onStopLoading(); // At this point we can release the resources associated with 'mData'. if (mData != null) { releaseResources(mData); mData = null; } } private void releaseResources(List<PhotoModel> data) { // For a simple List, there is nothing to do. For something like a Cursor, we // would close it in this method. All resources associated with the Loader // should be released here. if (mCursor != null && !mCursor.isClosed()) { mCursor.close(); } } public Uri getUri() { return mUri; } public void setUri(Uri uri) { mUri = uri; } public String[] getProjection() { return mProjection; } public void setProjection(String[] projection) { mProjection = projection; } public String getSelection() { return mSelection; } public void setSelection(String selection) { mSelection = selection; } public String[] getSelectionArgs() { return mSelectionArgs; } public void setSelectionArgs(String[] selectionArgs) { mSelectionArgs = selectionArgs; } public String getSortOrder() { return mSortOrder; } public void setSortOrder(String sortOrder) { mSortOrder = sortOrder; } }