Java tutorial
/* * Copyright (C) 2015 Jess Platas Varet * * 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. */ /* * This file is a derivative work of android.support.v4.content.CursorLoader * * Copyright (C) 2011 The Android Open Source Project */ package es.jpv.android.examples.loadersexample.db; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteOpenHelper; import android.net.Uri; import android.support.v4.content.AsyncTaskLoader; import java.io.FileDescriptor; import java.io.PrintWriter; import java.util.Arrays; /** * Allows to execute SQL SELECT statements on the UI thread asynchronously */ public class DBSelectCursorLoader extends AsyncTaskLoader<Cursor> { final ForceLoadContentObserver mObserver; SQLiteOpenHelper mDB; String mTable; String[] mProjection; String mSelection; String[] mSelectionArgs; String mSortOrder; Long mLimit; Cursor mCursor; /** * Runs a query asynchronously * * @return A Cursor object with the data */ @Override public Cursor loadInBackground() { Cursor cursor = mDB.getReadableDatabase().query(mTable, mProjection, mSelection, mSelectionArgs, null, null, mSortOrder, String.valueOf(mLimit)); if (cursor != null) { // Ensure the cursor window is filled cursor.getCount(); cursor.registerContentObserver(mObserver); } return cursor; } /* Runs on the UI thread */ @Override public void deliverResult(Cursor cursor) { if (isReset()) { // An async query came in while the loader is stopped if (cursor != null) { cursor.close(); } return; } Cursor oldCursor = mCursor; mCursor = cursor; if (isStarted()) { super.deliverResult(cursor); } if (oldCursor != null && oldCursor != cursor && !oldCursor.isClosed()) { oldCursor.close(); } } /** * Creates an empty unspecified DBSelectCursorLoader. You must follow this with * calls to {@link #setDB(SQLiteOpenHelper)}, {@link #setSelection(String)}, etc * to specify the query to perform. */ public DBSelectCursorLoader(Context context) { super(context); mObserver = new ForceLoadContentObserver(); } /** * Creates a fully-specified DBSelectCursorLoader. See * {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) * ContentResolver.query()} for documentation on the meaning of the * parameters. db refers to the instance of the SQLiteOpenHelper subclass used in the app */ public DBSelectCursorLoader(Context context, SQLiteOpenHelper db, String tableName, String[] projection, String selection, String[] selectionArgs, String sortOrder, Long limit) { super(context); mObserver = new ForceLoadContentObserver(); mDB = db; mTable = tableName; mProjection = projection; mSelection = selection; mSelectionArgs = selectionArgs; mSortOrder = sortOrder; mLimit = limit; } /** * Starts an asynchronous load of the 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. * * Must be called from the UI thread */ @Override protected void onStartLoading() { if (mCursor != null) { deliverResult(mCursor); } 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(Cursor cursor) { if (cursor != null && !cursor.isClosed()) { cursor.close(); } } @Override protected void onReset() { super.onReset(); // Ensure the loader is stopped onStopLoading(); if (mCursor != null && !mCursor.isClosed()) { mCursor.close(); } mCursor = null; } public SQLiteOpenHelper getDB() { return mDB; } public void setDB(SQLiteOpenHelper db) { mDB = db; } 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; } @Override public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) { super.dump(prefix, fd, writer, args); writer.print(prefix); writer.print("mUri="); writer.println(mDB); writer.print(prefix); writer.print("mProjection="); writer.println(Arrays.toString(mProjection)); writer.print(prefix); writer.print("mSelection="); writer.println(mSelection); writer.print(prefix); writer.print("mSelectionArgs="); writer.println(Arrays.toString(mSelectionArgs)); writer.print(prefix); writer.print("mSortOrder="); writer.println(mSortOrder); writer.print(prefix); writer.print("mCursor="); writer.println(mCursor); } /** * Executes a raw SQL statement asynchronously * * @param sql The SQL statement to execute. Arguments have to be written as ? * @param writeMode false if we want to access the database on read-only mode * @param bindArgs Arguments to be binded to the SQL statement */ public void execSQL(String sql, boolean writeMode, Object... bindArgs) { new DBAsyncTask(mDB, this).execute(sql, bindArgs, writeMode); } }