ios 任務、線程、定時器

一：operations（任務）

 

cocoa提供了三種不同的operations

 

1：Block operations（NSBlockOperation）
These facilitate 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;
                            <span>f</span>or (counter = 0;counter < 1000;counter++){
                                NSLog(@"Count = %lu", (unsigned long)counter);
                            }
                                }];

    /* Make sure we keep the re<span>f</span>erence somewhere */
    sel<span>f</span>.simpleOperation = newBlockOperation;

    /* Start the operation */
    [sel<span>f</span>.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:selfselector:@selector(simpleOperationEntry:) object:simpleObject];

[newOperation  start];

 

 

調用start方法執行改任務

 

#import <UIKit/UIKit.h>
@inter<span>f</span>ace 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 did<span>F</span>inishLaunchingWithOptions:(NSDictionary *)launchOptions {

    NSNumber *simpleObject = [NSNumber numberWithInteger:123];
    NSInvocationOperation *newOperation =[[NSInvocationOperation alloc] initWithTarget:sel<span>f</span> selector:@selector(simpleOperationEntry:) object:simpleObject];
    sel<span>f</span>.simpleOperation = newOperation;
    [newOperation release];

    [sel<span>f</span>.simpleOperation start];
    [window makeKeyAndVisible];
    return YES;
}

- (void)dealloc {

    [simpleOperation release];
    [window release];
    [super dealloc];
}

 

 

 

 

 

 

3：Plain operations（簡單的任務）NSOperation的子類

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.

 

 

@inter<span>f</span>ace MyTask : NSOperation {
    int operationId;
}

@property int operationId;

@end

 

這里的operationId屬性不是必須的

 

@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

 

 

必須
- (void)main;方法，[MyTask start]是執行main方法

 

 

二：任務隊列（NSOperationQueue）

 

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

 

 

以上三種Operation都可以添加到NSOperationQueue中，添加后立即被執行。

 

NSOperationQueue 可以設置最大並行執行任務數。默認值為-1無限制。

 

 

三：多個任務之間存在依賴關系

 

設置方式：

[self.firstOperation addDependency:self.secondOperation];

 

dependency：附屬的意思

 

把secondOperation做為firstOperation的附屬。因此先執行secondOperation，再執行firstOperation 。

 

 

四：延時執行某個方法

 

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 ... */
}

 

該方法只能接受一個參數。如果需要傳遞多個參數怎么辦呢???

     讓selector調用的方法接受的參數類型修改為Dictionary類型。

 

 

（1）如果調用的selector不接受參數則，withObject：nil

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

 

 

2：取消延時執行的方法

 

（1）cancelPreviousPerformRequestsWithTarget: 

（2） cancelPreviousPerformRequestsWithTarget:selector:object:

 

 

五：NSTimer

 

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

 

2：invalidate

調用invalidate方法，不僅是釋放NSTimer，還釋放userinfo對象。
如果repeats設置為NO，NSTimer在調用完成之后就知道失效，隨即釋放userinfo對象

 

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:

   （用該方式，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:

  （用該方式，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 響應函數定義格式

 

並需有一個NSTimer *類型的參數

 

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

 

 

 

六：NSThread

 

1：initWithTarget:selector:object:

 

2：detachNewThreadSelector:toTarget: withObject:

 

以上兩種方式，selector調用的函數，必須聲明自己的NSAutoreleasePool

 

 

3：performSelectorInBackground: withObject:

     一個簡單的方法來創建線程，而無需直接處理線程。

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

 

4:start

調用start方法啟動線程

 

5:cancel

調用cancel方法，並把變量賦值為nil

 

6:cancel vs exit

 

對於線程調用cancel方法停止，不要調用exit，因為exit方法沒有給線程清理自己並釋放資源的時間

 

7:線程的內存泄露

 

 - (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];-------------自動釋放池的范圍

 

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

調用改方法myImage 對象被添加進該新建線程的自動釋放池，但因為在這里沒有聲明NSAutoreleasePool 造成內存泄露

 

 /* This will NOT cause a memory leak */
[self performSelectorOnMainThread:@selector(allocateSomething)
withObject:nil
     waitUntilDone:YES];

 

調用改方法myImage 對象被放進主線程的自動釋放池，在主線程銷毀是被自動釋放