我对异步编程的概念很陌生，但我得到了它的一般要点（事情在后台运行）。
我遇到的问题是我有一种利用AFNetworking 2.0发出HTTP帖子请求的方法，它在大多数情况下都有效。
但是，我无法弄清楚如何在方法返回时让方法实际返回从响应中接收的值，然后THEN从响应中获取值。
-(int) registerUser
{
self.responseValue = 000; //Notice I set this to 000 at start of method
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.requestSerializer = [AFJSONRequestSerializer serializer];
NSDictionary *parameters = @{ @"Username": @"SomeUsername" };
[manager POST:@"http://XXX/register"
parameters:parameters
success:^(AFHTTPRequestOperation *operation, id responseObject)
{
NSLog(@"JSON: %@", responseObject);
NSError *err = nil;
self.responseValue = [[responseObject objectForKey:@"res"] intValue];
//Note: This^ value returns 99 and NSLogs confirm this
}
failure:^(AFHTTPRequestOperation *operation, NSError *err)
{
NSLog(@"Error: %@", err);
}];
return self.responseValue; //This will return 000 and never 99!
}
什么是正确的＆＃39;处理这种情况的方法？我听过使用“回调”的耳语，但在这种情况下，我真的不明白如何实现这一点。
任何指导或帮助都会很棒，欢呼！
答案 0 :(得分：1)
问题在于，POST异步运行，正如您所指出的那样，所以在实际return属性之前，您正在点击responseValue行设置，因为success块稍后运行。在其中放置断点/ NSLog语句，您将首先看到您正在点击return行。
您通常不会从异步方法中获取return值，而是采用完成块模式。例如：
- (void)registerUserWithCompletion:(void (^)(int responseValue, NSError *error))completion
{
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
manager.requestSerializer = [AFJSONRequestSerializer serializer];
NSDictionary *parameters = @{ @"Username": @"SomeUsername" };
[manager POST:@"http://XXX/register"
parameters:parameters
success:^(AFHTTPRequestOperation *operation, id responseObject)
{
NSLog(@"JSON: %@", responseObject);
int responseValue = [[responseObject objectForKey:@"res"] intValue];
if (completion)
completion(responseValue, nil);
}
failure:^(AFHTTPRequestOperation *operation, NSError *err)
{
NSLog(@"Error: %@", err);
if (completion)
completion(-1, err); // I don't know what you want to return if it failed, but handle it appropriately
}];
}
然后，您可以按如下方式使用它：
[self registerUserWithCompletion:^(int responseValue, NSError *error) {
if (error)
NSLog(@"%s: registerUserWithCompletion error: %@", __FUNCTION__, error);
else
NSLog(@"%d", responseValue);
// do whatever you want with that responseValue here, inside the block
}];
// Needless to say, don't try to use the `responseValue` here, because
// `registerUserWithCompletion` runs asynchronously, and you will probably
// hit this line of code well before the above block is executed. Anything
// that is dependent upon the registration must called from within the above
// completion block, not here after the block.
请注意，我建议您退出之前拥有的responseValue财产，因为现在您正在使用完成功能块，您可以通过该机制将其传回给您，而不是依靠在类属性上。
答案 1 :(得分：1)