ios 任务、线程、定时器

From : http://o0o0o0o.iteye.com/blog/1326772

一：operations（任务）

 

cocoa提供了三种不同的operations

 

1：Block operations（NSBlockOperation ）
These f acilitate the execution of one or more block objects.

 

 

#import <UIKit/UIKit.h>
@inter<span>f</span>ace OperationsAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
    NSBlockOperation *simpleOperation;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) NSBlockOperation *simpleOperation;

@end

 

#import "OperationsAppDelegate.h"

@implementation OperationsAppDelegate
@synthesize window;
@synthesize simpleOperation;

- (BOOL
) application:(UIApplication *)application did<span>F</span>inishLaunchingWithOptions:(NSDictionary *)launchOptions {
    /* Here is our block */
    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);
                            }
                                }];

    /* Make sure we keep the reference somewhere */
    self.simpleOperation = newBlockOperation;

    /* Start the operation */
    [self.simpleOperation start];

    /* Print something out just to test i<span>f</span> we have to wait
    <span>f</span>or the block to execute its code or not */

    NSLog(@"Main thread is here"
);
    [window makeKeyAndVisible];
    return
 YES;
}


- (void
)dealloc {
    [simpleOperation release];
    [window release];
    [super dealloc];
}

@end

 

 

2：Invocation operations（NSInvocationOperation ）
These allow you to invoke a method in another, currently existing object.

 

NSNumber *simpleObject = [NSNumber numberWithInteger:123];

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

[newOperation  start];

 

 

调用start方法执行改任务

 

#import <UIKit/UIKit.h>
@interface OperationsAppDelegate : NSObject <UIApplicationDelegate> {
    UIWindow *window;
    NSInvocationOperation *simpleOperation;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) NSInvocationOperation *simpleOperation;

@end

 

- (
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. The code to be executed
will be written inside the main method of the operation object.

 

 

@interface MyTask : NSOperation {
    int
 operationId;
}

@property int
 operationId;

@end

 

这里的operationId属性不是必须的

 

@implementation MyTask

@synthesize operationId;

- (void
)main{
    NSLog(@"task %i run … "
,operationId);
    [NSThread sleep<span>F</span>orTimeInterval:10];
    NSLog(@"task %i is <span>f</span>inished. "
,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.firstOperation addDependency :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:

 

 

- (
void
) connectionHasFailedWithError:(NSError *)paramError onRemoteURL:(NSURL *)paramRemoteURL{
    /* We failed to download the file. Attempt to download it again after 3 seconds */
    [self performSelector:@selector(attemptToDownloadRemoteURL:) withObject:paramRemoteURL afterDelay:3.0f];
}

- (void
) attemptToDownloadRemoteURL:(NSURL *)paramRemoteURL{
    /* Attempt to download the remote file again here by initializing
    a new connection ... */
}

 

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:

 

- (
void
) startPainting{
    SEL selectorToCall = @selector(paint:);
    NSMethodSignature *methodSignature = [[self class
] instanceMethodSignatureForSelector:selectorToCall];
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
    [invocation setTarget:self];
    [invocation setSelector:selectorToCall];

/* Start a scheduled timer now */
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）

 

- (
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）

- (
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

 

- (
void
) paint:(NSTimer *)paramTimer{
    /* Do something here */
    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。

[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

 

 - (
void
) newThreadEntryPoint{
    /* A thread without an autorelease pool to test the following code */
    //NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    /* This WILL cause a memory leak */
    [self performSelector:@selector(allocateSomething)];

    /* This will NOT cause a memory leak */
    [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];
    /* Do something with the image here */
}

- (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

 

/* This WILL cause a memory leak */
[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

 

 /* This will NOT cause a memory leak */
[self performSelectorOnMainThread:@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