如何在块内更改对象的值(作为参数传递) [英] How do I change object's value (passed as a parameter) inside block

问题描述

我的一个函数中有一个 POST 请求块，我想更改块内 NSString 对象的值.

I have an POST request block in one of my functions and I want to change the value of an NSString object inside the block.

我意识到通常可以只给变量 __block 加上前缀，但在我的例子中，想通过直接引用它的参数来更改 NSString 对象的值.

I realise that normally one could just prefix the variable __block, but in my case, want to change the value of an NSString object by directly referencing its parameter.

这是一个带有相关注释的代码框架.

Here's a code skeleton, with relevant comments.

- (void)getItemInformation:(NSString *)inputString{
    //setup stuff
    [manager  POST:@"http://foo.com/iphone_item_string/"
        parameters:parameters
           success:^(AFHTTPRequestOperation *operation, id responseObject) {
               //change inputString directly here
               inputString = (NSString *)responseObject[0];
               //this of course gives an error, but I'm
               //unsure of how to use __block with a parameter
           }
               //foo
           }
     ];
}

以及来自调用函数的一段

And a segment from the calling function

currentEntryData.foo = "lorem";
NSString *retrieveString;
[self getItemInformation:retrieveString];
currentEntryData.bar = retrieveString;
currentEntryData.oof = "ipsum";

推荐答案

可以使用块

- (void)getItemInformationWithCallback:(void(^)(NSString *resultString))callback {

    [manager POST:@"http://foo.com/iphone_item_string/"
        parameters:parameters
           success:^(AFHTTPRequestOperation *operation, id responseObject) {

               // Here you call the callback block
               //
               NSString *newString = (NSString *)responseObject[0];
               if (callback)
                   callback(newString)
           }
     }];
}

这就是你如何取回字符串

And that's how you get the string back

[self getItemInformationWithCallback:^(NSString *resultString) {
    NSLog(@"%@", resultString);
}];

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