iOS 多线程详解

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一：operations（任务）

cocoa提供了三种不同的operations

1：Block operations（NSBlockOperation）
These facilitate the execution of one ormore block objects.

代码

#import   @interface OperationsAppDelegate : NSObject  {      UIWindow *window;      NSBlockOperation *simpleOperation;  }    @property (nonatomic, retain) IBOutlet UIWindow *window;  @property (nonatomic, retain) NSBlockOperation *simpleOperation;    @end

代码

#import "OperationsAppDelegate.h"    @implementation OperationsAppDelegate  @synthesize window;  @synthesize simpleOperation;    - (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {            NSBlockOperation *newBlockOperation = [NSBlockOperation blockOperationWithBlock:^{                              NSLog(@"Main Thread = %@", [NSThread mainThread]);                              NSLog(@"Current Thread = %@", [NSThread currentThread]);                              NSUInteger counter = 0;                              for (counter = 0;counter < 1000;counter++){                                  NSLog(@"Count = %lu", (unsigned long)counter);                              }                                  }];              self.simpleOperation = newBlockOperation;                  [self.simpleOperation start];                    NSLog(@"Main thread is here");      [window makeKeyAndVisible];      return YES;  }      - (void)dealloc {      [simpleOperation release];      [window release];      [super dealloc];  }    @end

2：Invocationoperations（NSInvocationOperation）
These allow you to invoke a method in another, currently existingobject.

NSNumber *simpleObject = [NSNumber numberWithInteger:123];

NSInvocationOperation *newOperation = [[NSInvocationOperationalloc] initWithTarget:selfselector:@selector(simpleOperationEntry:) object:simpleObject];

[newOperation start];

调用start方法执行改任务

代码

#import   @interface OperationsAppDelegate : NSObject  {      UIWindow *window;      NSInvocationOperation *simpleOperation;  }    @property (nonatomic, retain) IBOutlet UIWindow *window;  @property (nonatomic, retain) NSInvocationOperation *simpleOperation;    @end

代码

- (void) simpleOperationEntry:(id)paramObject{        NSLog(@"Parameter Object = %@", paramObject);      NSLog(@"Main Thread = %@", [NSThread mainThread]);      NSLog(@"Current Thread = %@", [NSThread currentThread]);  }    - (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {        NSNumber *simpleObject = [NSNumber numberWithInteger:123];      NSInvocationOperation *newOperation =[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(simpleOperationEntry:) object:simpleObject];      self.simpleOperation = newOperation;      [newOperation release];        [self.simpleOperation start];      [window makeKeyAndVisible];      return YES;  }    - (void)dealloc {        [simpleOperation release];      [window release];      [super dealloc];  }

3：Plain operations（简单的任务）NSOperation的子类

These are plain operation classes that need to be subclassed. Thecode to be executed
will be written inside the main methodof the operation object.

代码

@interface MyTask : NSOperation {       int operationId;   }    @property int operationId;    @end

这里的operationId属性不是必须的

代码

@implementation MyTask    @synthesize operationId;    - (void)main{       NSLog(@"task %i run … ",operationId);       [NSThread sleepForTimeInterval:10];       NSLog(@"task %i is finished. ",operationId);   }    @end

必须
- (void)main;方法，[MyTask start]是执行main方法

二：任务队列（NSOperationQueue）

NSOperationQueue *newOperationQueue = [[NSOperationQueue alloc]init];
[ newOperationQueue addOperation:Operation];

以上三种Operation都可以添加到NSOperationQueue中，添加后立即被执行。

NSOperationQueue 可以设置最大并行执行任务数。默认值为-1无限制。

三：多个任务之间存在依赖关系

设置方式：

[self.firstOperationaddDependency:self.secondOperation];

dependency：附属的意思

把secondOperation做为firstOperation的附属。因此先执行secondOperation，再执行firstOperation。

四：延时执行某个方法

1：performSelector:withObject:afterDelay:

代码

- (void) connectionHasFailedWithError:(NSError *)paramError onRemoteURL:(NSURL *)paramRemoteURL{            [self performSelector:@selector(attemptToDownloadRemoteURL:) withObject:paramRemoteURL afterDelay:3.0f];  }    - (void) attemptToDownloadRemoteURL:(NSURL *)paramRemoteURL{        }

该方法只能接受一个参数。如果需要传递多个参数怎么办呢???

让selector调用的方法接受的参数类型修改为Dictionary类型。

（1）如果调用的selector不接受参数则，withObject：nil

（2）通过performSelector:withObjcet:afterDelay调用的方法不能有返回值

2：取消延时执行的方法

（1）cancelPreviousPerformRequestsWithTarget:

（2） cancelPreviousPerformRequestsWithTarget:selector:object:

五：NSTimer

1：scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:

2：invalidate

调用invalidate方法，不仅是释放NSTimer，还释放userinfo对象。
如果repeats设置为NO，NSTimer在调用完成之后就知道失效，随即释放userinfo对象

3：scheduledTimerWithTimeInterval:invocation:repeats:

代码

- (void) startPainting{      SEL selectorToCall = @selector(paint:);      NSMethodSignature *methodSignature = [[self class] instanceMethodSignatureForSelector:selectorToCall];      NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];      [invocation setTarget:self];      [invocation setSelector:selectorToCall];      NSTimer *newTimer =[NSTimer scheduledTimerWithTimeInterval:1.0                          invocation:invocation                             repeats:YES];        self.paintingTimer = newTimer;  }

4：timerWithTimeInterval:target:selector:userInfo:repeats:

（用该方式，需要把timer添加到runloop中）

代码

- (void) startPainting{      NSTimer *newTimer = [NSTimer timerWithTimeInterval:1.0                              target:self                            selector:@selector(paint:)                            userInfo:nil                             repeats:YES];        self.paintingTimer = newTimer;        [[NSRunLoop currentRunLoop] addTimer:self.paintingTimer forMode:NSDefaultRunLoopMode];  }

5：timerWithTimeInterval:invocation:repeats:

（用该方式，需要把timer添加到runloop中）

代码

- (void) startPainting{       SEL selectorToCall = @selector(paint:);      NSMethodSignature *methodSignature =[[self class] instanceMethodSignatureForSelector:selectorToCall];      NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];        [invocation setTarget:self];      [invocation setSelector:selectorToCall];      NSTimer *newTimer = [NSTimer timerWithTimeInterval:1.0                          invocation:invocation                             repeats:YES];      self.paintingTimer = newTimer;      [[NSRunLoop currentRunLoop] addTimer:self.paintingTimer                       forMode:NSDefaultRunLoopMode];  }

6：NSTimer 响应函数定义格式

并需有一个NSTimer *类型的参数

代码

- (void) paint:(NSTimer *)paramTimer{            NSLog(@"Painting");  }

六：NSThread

1：initWithTarget:selector:object:

2：detachNewThreadSelector:toTarget: withObject:

以上两种方式，selector调用的函数，必须声明自己的NSAutoreleasePool

3：performSelectorInBackground: withObject:

一个简单的方法来创建线程，而无需直接处理线程。

代码

  [self performSelectorInBackground:@selector(thirdCounter) withObject:nil];

4:start

调用start方法启动线程

5:cancel

调用cancel方法，并把变量赋值为nil

6:cancel vs exit

对于线程调用cancel方法停止，不要调用exit，因为exit方法没有给线程清理自己并释放资源的时间

7:线程的内存泄露

代码

- (void) newThreadEntryPoint{            //NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];                  [self performSelector:@selector(allocateSomething)];              [self performSelectorOnMainThread:@selector(allocateSomething)                  withObject:nil                   waitUntilDone:YES];      //[pool release];  }    - (void) allocateSomething{      NSBundle *mainBundle = [NSBundle mainBundle];      NSString *imagePath = [mainBundle pathForResource:@"MyImage" ofType:@"png"];      NSData *imageData = [NSData dataWithContentsOfFile:imagePath];      UIImage *myImage = [[[UIImage alloc] initWithData:imageData] autorelease];        }    - (void)viewDidLoad {        [NSThread detachNewThreadSelector:@selector(newThreadEntryPoint)                   toTarget:self                     withObject:nil];  }

UIImage *myImage = [[[UIImage alloc] initWithData:imageData]autorelease];-------------自动释放池的范围

[self performSelector:@selector(allocateSomething)];

调用改方法myImage 对象被添加进该新建线程的自动释放池，但因为在这里没有声明NSAutoreleasePool造成内存泄露

[selfperformSelectorOnMainThread:@selector(allocateSomething)
withObject:nil
waitUntilDone:YES];

调用改方法myImage 对象被放进主线程的自动释放池，在主线程销毁是被自动释放

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