如何在 GET 请求之外使用变量？

Question

我愿意：

• 在 GET 请求之前初始化变量 (AFNetworking)
• 赋值给请求成功内的变量
• 请求完成后使用变量

---

我得到的错误：

• 在 GET 请求之后尝试对变量执行某些操作时，它会中断，并声称该变量还没有任何值

---

以下是我的代码，我该如何解决这个问题？

- (IBAction)synchronisePressed {
    //Would like to initialise a variable here
    __block NSArray *received;
    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    [manager   GET:@"http://foo.com/foo/"
        parameters:nil
           success:^(AFHTTPRequestOperation *operation, id responseObject) {
               //Assign responseObject to received object
               received = responseObject;
               NSLog(@"Woo: %@", @"got here");
           }

           failure:^(AFHTTPRequestOperation *operation, NSError *error) {
               NSLog(@"Error: %@", error);
           }];
    //Now outside of request, so use array in some way
    [foo received];
}

Answer 1

问题不在代码或请求中。问题是 AFNetworking 的 GET 方法是异步的，您正在尝试同步使用它。

这意味着GET 方法将开始工作并在后台运行，其余代码将照常继续。只有当GET 请求完成后，块内的代码才会运行。

此代码是您开始请求后的 1 秒或 30 秒或任意时间。

在[foo received]; 行之前添加NSLog。

日志的顺序会是这样的......

1. Created NSArray called received.
2. Pass NSArray called received to method foo.
// some time later
3. AFNetworking GET request finished.
4. Assign value from the GET request to the NSArray called received.

在这种情况下，您需要做的是将您的调用放在完成块内的[foo received];。

这样的……

- (IBAction)synchronisePressed
{
    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];

    [manager   GET:@"http://foo.com/foo/"
        parameters:nil
           success:^(AFHTTPRequestOperation *operation, id responseObject) {
               //Assign responseObject to received object
               NSArray *received = responseObject;
               NSLog(@"Woo: %@", @"got here");
               [foo received];
           }

           failure:^(AFHTTPRequestOperation *operation, NSError *error) {
               NSLog(@"Error: %@", error);
           }];
}

现在你会得到...

1. Created NSArray called received.
// some time later
2. AFNetworking GET request finished.
3. Assign value from the GET request to the NSArray called received.
4. Pass NSArray called received to method foo.