是否有可能避免寫這個塊調用代碼'倒退'？

Question

我有一個Objective C中的異步方法，你傳遞一個完成處理程序。

我希望有條件地在兩個不同的對象上運行這個方法兩次，然後處理結果。

我可以找到做這項工作的唯一方法就是按照下面的方式寫代碼'向後'。

這意味着我的主要架構失敗。有沒有更好的辦法？

defines.h

#define BLOCK_SAFE_RUN(block, ...) block ? block(__VA_ARGS__) : nil 

myController.h

// Code executes in the order (0),(1),(2),(3),(4) - see comments 


    // (0) Create the origin completion handler 
    void (^originCompletionHandler)(FAPlacePoint *, BOOL, BOOL) = ^void (FAPlacePoint *savedOriginPP, BOOL geoCodeDidSucceed, BOOL saveDidSucceed) 
    { 

     // (2) Create the destination completion handler 
     void (^destinationCompletionHandler)(FAPlacePoint *, BOOL, BOOL) = ^void (FAPlacePoint *savedDestinationPP, BOOL geoCodeDidSucceed, BOOL saveDidSucceed) 
     { 

      // (4) 
      // Everything is finished. Do something with savedOriginPP and savedDestinationPP 


     }; 

     // (3) Conditionally run the geocode method with the dest point then call the destination completion handler 
     if (destinationPlacePoint.currentLocation) 
      [self reverseGeocodeThenSavePlacePoint:destinationPlacePoint completion:destinationCompletionHandler]; 
     else 
     { 
      FAPlacePoint * pp = [self storePlacePoint:destinationPlacePoint]; 
      BLOCK_SAFE_RUN(destinationCompletionHandler, pp, YES, YES); 
     } 


    }; 


    // (1) Conditionally run the geocode method with the origin point then call the origin completion handler 
    if (originPlacePoint.currentLocation) 
     [self reverseGeocodeThenSavePlacePoint:originPlacePoint completion:originCompletionHandler]; 
    else 
    { 
     FAPlacePoint * pp = [self storePlacePoint:originPlacePoint]; 
     BLOCK_SAFE_RUN(originCompletionHandler, pp, YES, YES); 
    } 

Answer 1

你有重複的代碼，所以應該分離到的方法：

- (void) processPoint:(FAPlacePoint*)point completionHandler:(void (^)(FAPlacePoint *savedPP, BOOL geoCodeDidSucceed, BOOL saveDidSucceed))completionHandler 
{ 
    if (point.currentLocation) 
     [self reverseGeocodeThenSavePlacePoint:point completion:completionHandler]; 
    else 
    { 
     FAPlacePoint * pp = [self storePlacePoint:point]; 
     BLOCK_SAFE_RUN(completionHandler, pp, YES, YES); 
    } 
} 

這可以讓你避免存儲在變量塊只是爲了避免重複它們。所以，你的代碼減少到：

[self processPoint:originPlacePoint completionHandler:^void (FAPlacePoint *savedOriginPP, BOOL geoCodeDidSucceed, BOOL saveDidSucceed) { 
    [self processPoint:destinationPlacePoint completionHandler:^void (FAPlacePoint *savedDestinationPP, BOOL geoCodeDidSucceed, BOOL saveDidSucceed) { 

     // Everything is finished. Do something with savedOriginPP and savedDestinationPP 

    }]; 
}]; 

Answer 2

這意味着在我的部分主要的建築失敗。有沒有更好的辦法？

不，它不。也許你只需要調整你的觀點。

在定義它之前，您不能使用變量來調用塊，因此類似完成處理程序的代碼將始終位於調用它的代碼之前。這沒什麼錯。這就像在執行之前告訴別人你的計劃：離開辦公室後，我會在雜貨店停下來。計算機語言通常不會有實際的將來時態，但它可能有助於在將它們稱爲未來時編寫代碼之前定義塊。

如果真的困擾你有導致它運行的代碼之前完成代碼，有時你可以把這些代碼在其自己的方法，這樣完成塊本身是由多一點打電話到該方法。當然，該方法可以跟隨調用它的代碼（但在使用完成塊本身之前仍需要定義它）。