在Swift中使用块给出错误“变量在其自己的初始值内使用”

Question

这是我在obj-c中的代码：

__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]; }];

这是Swift中转换后的代码：

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)
})

我已经转换并提出了这段代码。 一切都在这个代码中工作但我收到错误：

“在其自身初始值内使用的变量”

Answer 1

Swift编译器非常严格，在使用之前检查每个变量是否都有定义的值。 编译器不知道在您的情况下，只有在定义了requestReference变量之后才会执行闭包。

在这种情况下，您可以使用隐式解包的可选项：

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)
})

隐式展开的可选项是对编译器的承诺：变量现在没有值，但在使用时它将具有值。

Answer 2

首先定义它，然后使用它：

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