在Swift中使用塊給出錯誤“變量在其自己的初始值內使用”

Question

這是我在obj-c中的代碼：

__block NSString *requestReference = [self operation:method url:url parameters:parameters headers:headers success:^(NSURLSessionDataTask *task, id responseObject) {
NSError *error = [NSError errorWithSessionTask:task responseObject:responseObject];
if (error) {
    NSLog(@"error - %@", error);
    [delegate requestWithReference:requestReference didFinishWithBusinessError:error];
} else {
    id responseModel;
    if (modelClass && responseObject) {
        if ([responseObject isKindOfClass:[NSDictionary class]]) {
            // if response is a dictionary, create model out of it
            responseModel = [modelClass objectFromDictionary:responseObject error:&error];
        } else if ([responseObject isKindOfClass:[NSArray class]]) {
        }
    }
} } failure:^(NSURLSessionDataTask *task, NSError *error) {
[delegate requestWithReference:requestReference didFailWithError:error]; }];

這是Swift中轉換后的代碼：

var requestReference = self.operation(method, url: url, parameters: parameters, headers: headers, success: {(_ task: URLSessionDataTask, _ responseObject: Any) -> Void in
    var error = Error(sessionTask: task, responseObject: responseObject)
    if error {
        print("error - \(error)")
        delegate.request(with: requestReference, didFinishWithBusinessError: error)
    }
    else {
        var responseModel: Any!
        if modelClass && responseObject {
            if (responseObject is [AnyHashable: Any]) {
                // if response is a dictionary, create model out of it
                do {
                    responseModel = try modelClass.object(fromDictionary: responseObject)
                }
                catch {
                }
            }
            else if (responseObject is [Any]) {

            }
        }
    }
}, failure: {(_ task: URLSessionDataTask, _ error: Error) -> Void in
    delegate.request(with: requestReference, didFailWithError: error)
})

我已經轉換並提出了這段代碼。 一切都在這個代碼中工作但我收到錯誤：

“在其自身初始值內使用的變量”

Answer 1

Swift編譯器非常嚴格，在使用之前檢查每個變量是否都有定義的值。 編譯器不知道在您的情況下，只有在定義了requestReference變量之后才會執行閉包。

在這種情況下，您可以使用隱式解包的可選項：

var requestReference: String! 
requestReference = self.operation(..., success: {(_ task: URLSessionDataTask, _ responseObject: Any) -> Void in
    // ... 
    delegate.request(with: requestReference, didFinishWithBusinessError: error)
}, failure: {(_ task: URLSessionDataTask, _ error: Error) -> Void in
    delegate.request(with: requestReference, didFailWithError: error)
})

隱式展開的可選項是對編譯器的承諾：變量現在沒有值，但在使用時它將具有值。

Answer 2

首先定義它，然后使用它：

var requestReference = ""
requestReference = self.operation...