iOS：如何在後臺線程中使用數據來努力工作？

Question

我有這樣的方法：

- (BOOL)shouldDoSomeWork { 
    BOOL result = // here I need do hard work with data in background thread and return result, so main thread should wait until the data is calculated and then return result; 
    return result; 
} 

如何實現的？

Answer 1

您正在尋找這樣的：

-(void) startWork 
{ 
    //Show activity indicator 
    [NSThread detachNewThreadSelector:@selector(doSomeWork) toTarget:self withObject:nil]; 
} 

-(void) doSomeWork 
{ 
    NSAutoreleasePool *pool = [NSAutoreleasePool new]; 
    //Do your work here 
    [pool release]; 
    [self performSelectorOnMainThread:@selector(doneWork) withObject:nil waitUntilDone:NO]; 
} 

-(void) doneWork 
{ 
    //Hide activity indicator 
} 

Answer 2

示例如何使用GCD做到這一點：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 

     // Your hard code here 
     // ... 

     //BOOL result = ... 

     dispatch_async(dispatch_get_main_queue(),^{ 
      [self callbackWithResult:result]; // Call some method and pass the result back to main thread 
     }); 

    }); 

Answer 3

Commonadvice是利用現有的抽象的最高水平，你執行任務。因此，NSThread應該在後臺執行工作的列表中相對較低。

您調查的API的順序應該是這樣的：

1. NSOperation/NSOperationQueue
2. Grand Central Dispatch（libdispatch）
3. NSThread
4. POSIX線程

與前兩個你把你的代碼寫成一個「工作單元」，然後把這個工作o一個隊列在某個點執行。系統負責爲您創建和銷燬線程，並且API很容易處理。以下是使用NSOperationQueue的示例。

NSBlockOperation * blockOperation = [NSBlockOperation blockOperationWithBlock:^{ 
    //Do work 


    //update your UI on the main thread. 
    [self performSelectorOnMainThread:@selector(workDone:) withObject:workResults waitUntilDone:NO]; 
}]; 

[self.operationQueue addOperation:blockOperation]; 

那樣容易。

Answer 4

這通常不會如何做到。您需要更像這樣的結構：

- (void)doSomeWorkAndThen:(^void)block { 
    dispatch_async(dispatch_get_global_queue(0, 0),^{ 
    // do 
    // some 
    // work 
    dispatch_sync(dispatch_get_main_queue(),^{ 
     block(); 
    }); 
    }); 

也就是說，您將請求和事後處理保存在一個地方。