content: /*
   * Copyright (C) 2012 ZXing authors
   *
   * 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.google.zxing.camera;
  
  import java.util.ArrayList;
  import java.util.Collection;
  
  import android.content.Context;
  import android.content.SharedPreferences;
  import android.hardware.Camera;
  import android.os.AsyncTask;
  import android.preference.PreferenceManager;
  import android.util.Log;
  import com.google.zxing.common.Runnable;
  import com.google.zxing.config.Config;
  
  /**
   * 由于对焦不是一次性完成的任务（手抖），而系统提供的对焦仅有Camera.autoFocus()方法，
   * 因此需要一个线程来不断调用Camera.autoFocus()直到用户满意按下快门为止
   */
  final class AutoFocusManager implements Camera.AutoFocusCallback {
  
  	private static final String TAG = AutoFocusManager.class.getSimpleName();
  
  	private static final long AUTO_FOCUS_INTERVAL_MS = 2000L;
  	private static final Collection<String> FOCUS_MODES_CALLING_AF;
  	static {
  		FOCUS_MODES_CALLING_AF = new ArrayList<String>(2);
  		FOCUS_MODES_CALLING_AF.add(Camera.Parameters.FOCUS_MODE_AUTO);
  		FOCUS_MODES_CALLING_AF.add(Camera.Parameters.FOCUS_MODE_MACRO);
  	}
  
  	private boolean active;
  	private final boolean useAutoFocus;
  	private final Camera camera;
  	private AsyncTask<?, ?, ?> outstandingTask;
  
  	AutoFocusManager(Context context, Camera camera) {
  		this.camera = camera;
  		SharedPreferences sharedPrefs = PreferenceManager
  				.getDefaultSharedPreferences(context);
  		String currentFocusMode = camera.getParameters().getFocusMode();
  		useAutoFocus = sharedPrefs.getBoolean(Config.KEY_AUTO_FOCUS, true)
  				&& FOCUS_MODES_CALLING_AF.contains(currentFocusMode);
  		Log.i(TAG, "Current focus mode '" + currentFocusMode
  				+ "'; use auto focus? " + useAutoFocus);
  		start();
  	}
  
  	@Override
  	public synchronized void onAutoFocus(boolean success, Camera theCamera) {
  		if (active) {
  			outstandingTask = new AutoFocusTask();
  			Runnable.execAsync(outstandingTask);
  		}
  	}
  
  	synchronized void start() {
  		if (useAutoFocus) {
  			active = true;
  			try {
  				camera.autoFocus(this);
  			}
  			catch (RuntimeException re) {
  				// Have heard RuntimeException reported in Android 4.0.x+;
  				// continue?
  				Log.w(TAG, "Unexpected exception while focusing", re);
  			}
  		}
  	}
  
  	synchronized void stop() {
  		if (useAutoFocus) {
  			try {
  				camera.cancelAutoFocus();
  			}
  			catch (RuntimeException re) {
  				// Have heard RuntimeException reported in Android 4.0.x+;
  				// continue?
  				Log.w(TAG, "Unexpected exception while cancelling focusing", re);
  			}
  		}
  		if (outstandingTask != null) {
  			outstandingTask.cancel(true);
  			outstandingTask = null;
  		}
  		active = false;
  	}
  
  	private final class AutoFocusTask extends AsyncTask<Object, Object, Object> {
  		@Override
  		protected Object doInBackground(Object... voids) {
  			try {
  				Thread.sleep(AUTO_FOCUS_INTERVAL_MS);
  			}
  			catch (InterruptedException e) {
  				// continue
  			}
  			synchronized (AutoFocusManager.this) {
  				if (active) {
  					start();
  				}
  			}
  			return null;
  		}
  	}
  
  }
  