如何從GCD返回UIImage類型

Question

我有一個名爲「ComLog」的「UIImage」返回類型方法。我想從這個方法返回一個圖像。在「ComLog」方法中，我使用GCD從數組中獲取圖像值。我使用下面的代碼，「NSLog（@」qqqqqqqqqqq％@「，exiIco）」打印'image'的值，但NSLog（@「qqqqqqqqqqqq％@」，exiIco）;「不要 這裏是細節：

-(UIImage*) ComLog 
{ 
ExibitorInfo *currentExibitor100 = [[ExibitorInfo alloc] init]; 
currentExibitor100 = [self.exibitorsArray objectAtIndex:0]; 

imageQueueCompanyLogo = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); 
dispatch_async(imageQueueCompanyLogo,^
{ 
    UIImage *imageCompanyLogo = [UIImage imageWithData:[NSData dataWithContentsOfURL: [NSURL URLWithString:[currentExibitor100 companyLogoURL]]]]; 
    dispatch_async(dispatch_get_main_queue(),^
    { 
     self.exibitorIcoImageView.image = imageCompanyLogo; 
     exiIco = imageCompanyLogo; 
     NSLog(@"qqqqqqqqqqq %@", exiIco); 
    }); 
}); 
return exiIco; 
} 


- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    UIImage *a = [self ComLog]; 
    NSLog(@"It should be a image %@", a); 
} 

這裏所有屬性全局聲明（在「Myclass.h」文件）。我在目的C.新，如果你知道答案，請給予答覆。 在此先感謝。

Answer 1

第一總之，我建議您閱讀關於Objective C中的塊。您在函數內部使用的dispatch_async塊是異步的，因此在使用它之後會立即返回，因爲它在它自己的池中運行。調用另一種方法t o返回塊內的圖像處理，或在圖像準備就緒後張貼NSNotification。像這樣：

-(void) ComLog 
{ 
    ExibitorInfo *currentExibitor100 = [[ExibitorInfo alloc] init]; 
    currentExibitor100 = [self.exibitorsArray objectAtIndex:0]; 

    imageQueueCompanyLogo = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); 
    dispatch_async(imageQueueCompanyLogo,^
    { 
     UIImage *imageCompanyLogo = [UIImage imageWithData:[NSData dataWithContentsOfURL: [NSURL URLWithString:[currentExibitor100 companyLogoURL]]]]; 
     dispatch_async(dispatch_get_main_queue(),^
         { 
          self.exibitorIcoImageView.image = imageCompanyLogo; 
          exiIco = imageCompanyLogo; 
          NSLog(@"qqqqqqqqqqq %@", exiIco); 
          [self imageIsReady:exiIco]; 
         }); 
    }); 
// return exiIco; 
} 

- (void)imageIsReady:(uiimage *)image 
{ 
    //do whatever you want with the image 
    NSLog(@"Image is here %@", image); 
} 

Answer 2

你的代碼片段有太多錯誤，很難決定從哪裏開始。

我建議現在就離開GCD，稍後當你更有經驗時再看看它。

基本上，您想要從遠程服務器加載圖像。 NSURLConnection爲此提供了一個方便的方法這足以滿足非常簡單的用例：

+ (void)sendAsynchronousRequest:(NSURLRequest *)request queue:(NSOperationQueue *)queue completionHandler:(void (^)(NSURLResponse*, NSData*, NSError*))handler;

您可以在這裏找到的文檔：NSURLConnection Class Reference。

加載遠程資源的推薦方法是使用NSURLConnection以異步模式實現代理。你可以在這裏找到更多的信息： URL Loading System Programming Guide - Using NSURL Connection

我也建議閱讀Conventions。

下面是一個簡短示例如何使用sendAsynchronousRequest：執行塊

NSURL* url = [NSURL URLWithString:[currentExibitor100 companyLogoURL]]; 
NSMutableURLRequest* urlRequest = [NSURLRequest requestWithURL:url];  
NSOperationQueue* queue = [[NSOperationQueue alloc] init]; 

[NSURLConnection sendAsynchronousRequest:urlRequest 
            queue:queue  
         completionHandler:^(NSURLResponse* response, 
                NSData* data, 
               NSError* error) 
{ 
    if (data) {   
     // check status code, and optionally MIME type 
     if ([(NSHTTPURLResponse*)(response) statusCode] == 200 /* OK */) { 
      UIImage* image = [UIImage imageWithData:data]; 
      if (image) { 
       dispatch_async(dispatch_get_main_queue(), ^{ 
        self.exibitorIcoImageView.image = image; 
       }); 
      } else { 
       NSError* err = [NSError errorWithDomain: ...]; 
       [self handleError:err]; // execute on main thread! 
      }     
     } 
     else { 
      // status code indicates error, or didn't receive type of data requested 
      NSError* err = [NSError errorWithDomain:...]; 
      [self handleError:err]; // execute on main thread! 
     }      
    } 
    else { 
     // request failed - error contains info about the failure 
     [self handleError:error]; // execute on main thread! 
    }   
}];