IOS4以上的多任务

一：了解multitasking

        background apps(可以在后台运行的任务):

             1:play audio 

             2:get location

             3:voip stream

             4:request time to finish

             5: create notifications

 

二：多任务生命周期

 

1：程序加载成功

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

 

2：程序将要失去活跃状态

- (void)applicationWillResignActive:(UIApplication *)application

 

3：程序已经进入后台运行

- (void)applicationDidEnterBackground:(UIApplication *)application

 

4：程序将要进入前台运行

- (void)applicationWillEnterForeground:(UIApplication *)application

 

5：程序进入活跃状态

- (void)applicationDidBecomeActive:(UIApplication *)application

 

6：程序退出

- (void)applicationWillTerminate:(UIApplication *)application

 

 

从启动到转入后台，从后台转入前台，退出，生命周期函数调用顺序

1->5->2->3->4->5->6

 

 

三：转入后台后请求一段时间完成操作

 

 UIBackgroundTaskIdentifier backgroundTask;



 - (void)applicationDidEnterBackground:(UIApplication *)application {



   // tell the OS you're about to begin a background task that may need time to finish


     backgroundTask = [application beginBackgroundTaskWithExpirationHandler: ^{
         // 如果超时这个block将被调用
         dispatch_async(dispatch_get_main_queue(), ^{
             if (backgroundTask != UIBackgroundTaskInvalid)
             {
     // do whatever needs to be done
                 [application endBackgroundTask:backgroundTask];
                 backgroundTask = UIBackgroundTaskInvalid;
             }
         });
     }];


     // Start the long-running task
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

         // Do the work!
   [NSThread sleepForTimeInterval:5];
   NSLog(@"Time remaining: %f",[application backgroundTimeRemaining]);
   [NSThread sleepForTimeInterval:5];
   NSLog(@"Time remaining: %f",[application backgroundTimeRemaining]);
   [NSThread sleepForTimeInterval:5];
   NSLog(@"Time remaining: %f",[application backgroundTimeRemaining]);
   // done!

         // call endBackgroundTask - should be executed back on
   // main thread
         dispatch_async(dispatch_get_main_queue(), ^{
             if (backgroundTask != UIBackgroundTaskInvalid)
             {
     // if you don't call endBackgroundTask, the OS will exit your app.
                 [application endBackgroundTask:backgroundTask];
                 backgroundTask = UIBackgroundTaskInvalid;
             }
         });
     });

  NSLog(@"Reached the end of ApplicationDidEnterBackground - I'm done!");

 }

 

 

四：本地消息

 

1：创建一个本地消息

 

 -(IBAction) scheduleNotification {
     UILocalNotification *local = [[UILocalNotification alloc] init];

  // create date/time information
  local.fireDate = [NSDate dateWithTimeIntervalSinceNow:15];
     local.timeZone = [NSTimeZone defaultTimeZone];

  // set notification details
     local.alertBody = @"Missing you already!";
     local.alertAction = @"View";

  // set the badge on the app icon
     local.applicationIconBadgeNumber = 1;

  // Gather any custom data you need to save with the notification
     NSDictionary *customInfo =
  [NSDictionary dictionaryWithObject:@"ABCD1234" forKey:@"yourKey"];
     local.userInfo = customInfo;

  // Schedule it!
     [[UIApplication sharedApplication] scheduleLocalNotification:local];

  [local release];

 }

 

 

2：delegate 处理方法

 

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

     // Override point for customization after application launch.

     // Add the view controller's view to the window and display.
     [window addSubview:viewController.view];
     [window makeKeyAndVisible];

  //程序启动是检查是否有UILocalNotification，如果有跳出提示框
 // reset badge
  application.applicationIconBadgeNumber = 0;

     // If the app was closed, and we launched from the notification
     UILocalNotification *local =
     [launchOptions objectForKey:UIApplicationLaunchOptionsLocalNotificationKey];
     if (local) {
         UIAlertView *alert = [[UIAlertView alloc]
          initWithTitle:@"You came back! (App was closed)"
        message:@"Nice to see you again!" delegate:nil
        cancelButtonTitle:@"Okay" otherButtonTitles:nil];
   [alert show];
   [alert release];
     }


  return YES;
 }

 

 

 //如果程序完全退出，此方法不会被调用，而是先调用didFinishLaunchingWithOptions把程序启动起来。如果该程序在后台运行收到消息时直接调用该方法
 - (void)application:(UIApplication *)application
 didReceiveLocalNotification:(UILocalNotification *)local {

  // reset badge number
  application.applicationIconBadgeNumber = 0;

  if (local) {
   // get custom info from dictionary
   NSString *customInfo = [local.userInfo objectForKey:@"yourKey"];
   //
         UIAlertView *alert = [[UIAlertView alloc]
          initWithTitle:@"You came back! (App was running)"
          message:customInfo delegate:nil
          cancelButtonTitle:@"Okay" otherButtonTitles:nil];
   [alert show];
   [alert release];
     }
 }

 

 

 

五：后台播放音乐

 

 

1：读取文件

 

 - (void)viewDidLoad {
     [super viewDidLoad];

  self.playPauseButton.titleLabel.text == @"play";

  // grab the path to the caf file
  NSString *soundFilePath =
  [[NSBundle mainBundle] pathForResource: @"Rainstorm"
          ofType: @"mp3"];

  NSURL *fileURL = [[NSURL alloc] initFileURLWithPath: soundFilePath];

  // create a new AVAudioPlayer initialized with the URL to the file
  AVAudioPlayer *newPlayer =
  [[AVAudioPlayer alloc] initWithContentsOfURL: fileURL
              error: nil];
  [fileURL release];

  // set our ivar equal to the new player
  self.player = newPlayer;
  [newPlayer release];

  // preloads buffers, gets ready to play
  [player prepareToPlay];

  // set delegate so we can get called back when the sound has finished playing
  [player setDelegate: self];


   //重要的两行
   // set category of audio
  [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
  // announce that we want to hook up to remote UI events
  [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];


 }

 

 

2：重写canBecomeFirstResponder 方法，使改view 可以成为第一响应者

 -(BOOL) canBecomeFirstResponder {
        return YES;
 }

 

 3：显示view时，设置为第一响应者

 -(void) viewDidAppear:(BOOL)animated {
        [self becomeFirstResponder];
 }

 

 

4：实现remoteControlReceivedWithEvent方法使程序接收 iphone 自动音乐控制事件

 

 -(void) remoteControlReceivedWithEvent:(UIEvent *)event {
  switch (event.subtype) {
        case UIEventSubtypeRemoteControlTogglePlayPause:
                 [self playPause];
        default:
        break;
      }
 }

 

 5：info.plist 设置，可以设置多种形式

 

 <key>UIBackgroundModes</key>
 <array>
  <string>audio</string>
 </array>

 

 

 六：NSUserDefaults  问题

 

如果程序在后台挂起，在转入到前台后不会调用viewDidLoad 方法，所以要在viewDidLoad 方法里面注册UIApplicationWillEnterForegroundNotification ，调用loadSettings

 

 -(void) loadSettings: (NSNotification *) notification {
          NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
          [defaults synchronize];
   }

 

 // Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
 - (void)viewDidLoad {

  [self loadSettings:nil];

  NSNotificationCenter *notificationCenter = [NSNotificationCenter defaultCenter];
  [notificationCenter addObserver:self
       selector:@selector(loadSettings:)
       name:UIApplicationWillEnterForegroundNotification
         object:nil];

     [super viewDidLoad];
 }

 

 

 

七：去除后台运行inof.list

 

application dose not run in background   设置为  true