DataLoaderFragment.java

/*
 * Copyright (C) 2013 Ian G. Clifton
 * Code featured in Android User Interface Design: Turning Ideas and
 * Sketches into Beautifully Designed Apps (ISBN-10: 0321886739;
 * ISBN-13: 978-0321886736).
 *
 * 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 com.iangclifton.auid.ch10.splashscreenfragment;

import android.app.Activity;
import android.app.Fragment;
import android.os.AsyncTask;

/**
 * A Fragment with no UI that can load data.
 * 
 * To use, call {@link #setProgressListener(ProgressListener)} and then
 * {@link #startLoading()}.  You can check for a result at any point
 * with {@link #getResult()}.
 * 
 * @author Ian G. Clifotn
 */
public class DataLoaderFragment extends Fragment {
	
	/**
	 * Classes wishing to be notified of loading progress/completion implement this.
	 */
	public interface ProgressListener {
		/**
		 * Notifies that the task has completed
		 * 
		 * @param result Double result of the task
		 */
		public void onCompletion(Double result);
		
		/**
		 * Notifies of progress
		 * 
		 * @param value int value from 0-100
		 */
		public void onProgressUpdate(int value);
	}
	
	private ProgressListener mProgressListener;
	private Double mResult = Double.NaN;
	private LoadingTask mTask;
	
	@Override
	public void onAttach(Activity activity) {
		super.onAttach(activity);
		
		// Keep this Fragment around even during config changes
		setRetainInstance(true);
	}
	
	/**
	 * Returns the result or {@value Double#NaN}
	 * 
	 * @return the result or {@value Double#NaN}
	 */
	public Double getResult() {
		return mResult;
	}
	
	/**
	 * Returns true if a result has already been calculated
	 * 
	 * @return true if a result has already been calculated
	 * @see #getResult()
	 */
	public boolean hasResult() {
		return !Double.isNaN(mResult);
	}
	
	/**
	 * Removes the ProgressListener
	 * 
	 * @see #setProgressListener(ProgressListener)
	 */
	public void removeProgressListener() {
		mProgressListener = null;
	}
	
	/**
	 * Sets the ProgressListener to be notified of updates
	 * 
	 * @param listener ProgressListener to notify
	 * @see #removeProgressListener()
	 */
	public void setProgressListener(ProgressListener listener) {
		mProgressListener = listener;
	}
	
	/**
	 * Starts loading the data
	 */
	public void startLoading() {
		mTask = new LoadingTask();
		mTask.execute();
	}

	private class LoadingTask extends AsyncTask<Void, Integer, Double> {
		
		@Override
		protected Double doInBackground(Void... params) {
			double result = 0;
			for (int i = 0; i < 100; i++) {
				try {
					result += Math.sqrt(i);
					Thread.sleep(50);
					this.publishProgress(i);
				} catch (InterruptedException e) {
					return null;
				}
			}
			return Double.valueOf(result);
		}

		@Override
		protected void onPostExecute(Double result) {
			mResult = result;
			mTask = null;
			if (mProgressListener != null) {
				mProgressListener.onCompletion(mResult);
			}
		}

		@Override
		protected void onProgressUpdate(Integer... values) {
			if (mProgressListener != null) {
				mProgressListener.onProgressUpdate(values[0]);
			}
		}
	}
}