iphone 線程總結— detachNewThreadSelector的使用

不管是iphone中還是其他的作業系統，多線程在各種程式設計語言中都是難點，很多語言中實作起來很麻煩，objective-c雖然源于c,但其多線程程式設計卻相當簡單，可以與java相媲美。多線程程式設計是防止主線程堵塞，增加運作效率等等的最佳方法。而原始的多線程方法存在很多的毛病，包括線程鎖死等。

一、線程建立與啟動

線程建立主要有二種方式：

 
 (id)init; // designated initializer         
      
 (id)initWithTarget:(id)target selector:         
      
 (SEL)selector object:(id)argument;        
     
    

當然，還有一種比較特殊，就是使用所謂的convenient method，這個方法可以直接生成一個線程并啟動它，而且無需為線程的清理負責。這個方法的接口是：

 
 (void)detachNewThreadSelector:         
      
 (SEL)aSelector toTarget:         
      
 (id)aTarget withObject:         
      
 (id)anArgument        
     
    

前兩種方法建立後，需要手機啟動，啟動的方法是：

 
 (void)start;        
     
    

二、線程的同步與鎖

要說明線程的同步與鎖，最好的例子可能就是多個視窗同時售票的售票系統了。我們知道在java中，使用synchronized來同步，而iphone雖然沒有提供類似java下的synchronized關鍵字，但提供了NSCondition對象接口。檢視NSCondition的接口說明可以看出，NSCondition是iphone下的鎖對象，是以我們可以使用NSCondition實作iphone中的線程安全。這是來源于網上的一個例子：

SellTicketsAppDelegate.h 檔案

 
 // SellTicketsAppDelegate.h         
      
 import <UIKit/UIKit.h>        
      
 @interface SellTicketsAppDelegate : NSObject <UIApplicationDelegate> {         
      
      int tickets;         
      
      int count;         
      
      NSThread* ticketsThreadone;         
      
      NSThread* ticketsThreadtwo;         
      
      NSCondition* ticketsCondition;         
      
      UIWindow *window;         
      
 }         
      
 @property (nonatomic, retain) IBOutlet UIWindow *window;         
      
 @end         
      
 SellTicketsAppDelegate.m 檔案         
      
 // SellTicketsAppDelegate.m         
      
 import "SellTicketsAppDelegate.h"         
      
 @implementation SellTicketsAppDelegate         
      
 @synthesize window;         
      
 - (void)applicationDidFinishLaunching:(UIApplication *)application {         
      
      tickets = 100;         
      
      count = 0;         
      
      // 鎖對象         
      
      ticketCondition = [[NSCondition alloc] init];         
      
      ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];         
      
      [ticketsThreadone setName:@"Thread-1"];         
      
      [ticketsThreadone start];         
      
      ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];         
      
      [ticketsThreadtwo setName:@"Thread-2"];         
      
      [ticketsThreadtwo start];         
      
      //[NSThread detachNewThreadSelector:@selector(run) toTarget:self withObject:nil];         
      
       // Override point for customization after application launch         
      
      [window makeKeyAndVisible];         
          
 }         
          
 - (void)run{         
      
      while (TRUE) {         
      
      // 上鎖         
      
          [ticketsCondition lock];         
      
          if(tickets > 0){         
      
              [NSThread sleepForTimeInterval:0.5];         
      
              count = 100 - tickets;         
      
              NSLog(@"目前票數是:%d,售出:%d,線程名:%@",tickets,count,[[NSThread currentThread] name]);         
      
              tickets--;         
      
          }else{         
      
              break;         
      
          }         
      
          [ticketsCondition unlock];         
      
      }         
      
 }         
      
 - (void)dealloc {         
      
 [ticketsThreadone release];         
      
      [ticketsThreadtwo release];         
      
      [ticketsCondition release];          
      
      [window release];         
      
      [super dealloc];         
      
 }         
      
 @end        
     
    

三、線程的互動

線程在運作過程中，可能需要與其它線程進行通信，如在主線程中修改界面等等，可以使用如下接口：

 
 (void)performSelectorOnMainThread:         
      
 (SEL)aSelector withObject:         
      
 (id)arg waitUntilDone:         
      
 (BOOL)wait        
     
    

由于在本過程中，可能需要釋放一些資源，則需要使用NSAutoreleasePool來進行管理,如：

 
 (void)startTheBackgroundJob {              
      
 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];         
      
     // to do something in your thread job         
      
     ...         
      
     [self performSelectorOnMainThread:@selector(makeMyProgressBarMoving) withObject:nil waitUntilDone:NO];         
      
     [pool release];         
      
 }        
     
         
 
  

 
 
  
  
舉例說明怎麼簡單的建立一個子線程。

  
用到的類是NSThread類，這裡使用detachNewTheadSelector:toTagaet:withObject建立一個線程。

  
函數setupThread:(NSArray*)userInfor。通過userInfor将需要的資料傳到線程中。

  
函數定義：

  


  
           
 [代碼]c#/cpp/oc代碼：       
    

01	-( void )setupThread:(NSArray*)userInfor{

02

03	[NSThread detachNewThreadSelector:@selector(threadFunc:) toTarget:self withObject:(id)userInfor];

04

05

}

06

07	- ( void )threadFunc:(id)userInfor{

08

09	NSAutoreleasePool*pool = [[NSAutoreleasePool alloc] init];

10

11	//。。。。需要做的處理。

12

13	//這裡線程結束後立即傳回

14

15	[self performSelectorOnMainThread:@selector(endThread) withObject:nil waitUntilDone:NO];

16

17	[pool release];

18

19

}

performSelectorOnMainThread通知主線程執行函數endThread。也可以使用performSelector:onThread:withObject:waitUntil 通知某線程執行線程結束後的處理。

線程内不要重新整理界面。如果需要重新整理界面，通過performSelectorOnMainThread，調出主線程中的方法去重新整理。

例如，啟動一個線程下載下傳圖檔：

//啟動線程

[NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:url];

//線程函數

[代碼]c#/cpp/oc代碼：

01	- ( void ) downloadImage:(NSString*)url{

02

03	_subThreed = [NSThread currentThread];

04

05	self.uploadPool = [[NSAutoreleasePool alloc] init];

06	self.characterBuffer = [NSMutableData data];

07	done = NO;

08	[[NSURLCache sharedURLCache] removeAllCachedResponses];

09

10	NSMutableURLRequest *theRequest = [NSMutableURLRequest requestWithURL:[NSURLURLWithString:url]];

11

12	self.connection = [[NSURLConnection alloc] initWithRequest:theRequest  delegate :self];

13	[self performSelectorOnMainThread:@selector(httpConnectStart) withObject:nil waitUntilDone:NO];

14	if (connection != nil) {

15

do {

16	[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];

17	}  while (!done);

18

}

19

20	self.photo = [UIImage imageWithData:characterBuffer];

21

22

23	//下載下傳結束，重新整理

24	[self performSelectorOnMainThread:@selector(fillPhoto) withObject:nil waitUntilDone:NO];

25

26	// Release resources used only in this thread.

27	self.connection = nil;

28	[uploadPool release];

29	self.uploadPool = nil;

30

31	_subThreed = nil;

32

}

33

34

35

36	#pragma mark NSURLConnection Delegate methods

37

38

/*

39	Disable caching so that each time we run this app we are starting with a clean slate. You may not want to do this in your application.

40

*/

41	- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {

42

43	return nil;

44

}

45

46	// Forward errors to the delegate.

47	- ( void )connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {

48	done = YES;

49	[self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];

50	[characterBuffer setLength:0];

51

52

}

53

54	// Called when a chunk of data has been downloaded.

55	- ( void )connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

56	// Process the downloaded chunk of data.

57

58	[characterBuffer appendData:data];

59

60

}

61

62	- ( void )connectionDidFinishLoading:(NSURLConnection *)connection {

63

64	[self performSelectorOnMainThread:@selector(httpConnectEnd) withObject:nil waitUntilDone:NO];

65	// Set the condition which ends the run loop.

66	done = YES;

67

68

}

首先我們需要建立一個線程有兩種方法：

- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument

+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument

因為第二種方法不用對線程進行清理，是以我們常用第二種哦個方法。

[NSThread detachNewThreadSelector:@selector(new:) toTarget:self withObject:nil];

- (void)new:(id)sender{

[_myCondition lock];

//performSelectorInBackgroud主要進行邏輯上處理

[self performSelectorInBackgroud:@selector(doInBackgroud:) withObject:nil];

//perfomSelectorOnMainThread主要進行界面UI上的處理

[self perfomSelectorOnMainThread:@selector(doOnMain:) withObject:nil];

//[NSThread sleepForTimeInterval:n];

[_myCondition signal];

[_myCondition unlock];

[NSThread exit];

return;

}