Question

我有一个带有单个方法的类，它使用URLConnection将序列化的NSDictionary发送到某个URL的脚本，然后调用完成块。以下是该方法的代码：

- (void)sendDictionary:(NSDictionary *)dictionary toScript:(NSString *)scriptName completion:(void (^) (id response))completionBlock
{

    ...Serialize data and add it to an NSURLRequest request...

    H2URLConnection *connection = [[H2URLConnection alloc]initWithRequest:request];

    //Define a semaphore to block execution of later statements until the signal is received.
    dispatch_semaphore_t sem = dispatch_semaphore_create(0);

    [connection setCompletionBlock:[^(id obj, NSError *err)
     {
         if (!err) {
            //Catch the server response
             NSString *receivedString = [[NSString alloc] initWithData:obj encoding:NSUTF8StringEncoding];
             NSLog( @"ChecklistAppNetworkManager received string: %@", receivedString);

             //Convert the JSON response into an NSDictionary
             NSError *otherError;
             id deserializedJSON = [NSJSONSerialization JSONObjectWithData:obj options:kNilOptions error:&otherError];

             if (otherError) {
                 NSLog(@"ChecklistAppNetworkManager JSON Error: %@", otherError.description);
             }

             [completionBlock invoke];

             NSLog(@"ChecklistAppNetworkManager JSON Response: %@", deserializedJSON);

             //Dispatch the semaphore signal so that the main thread continues.
             dispatch_semaphore_signal(sem);

         } else {
             NSLog(@"ChecklistAppNetworkManager encountered an error connecting to the server: %@", [err description]);
         }

     }copy]];
    //Finalize and initate the connection.
    [connection start];

    //Since block is dispatched to main queue, stall with a loop until the semaphore signal arrives.
    while (dispatch_semaphore_wait(sem, DISPATCH_TIME_NOW)) {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:10]];
    }
}

我试图在另一个类中调用此类的实例，其中定义了完成块。这是我获得EXC_BAD_ACCESS的代码：

- (void)doSomeServerTask
{
    H2ChecklistAppNetworkManager *currentNetworkManager = ((H2AppDelegate *)[[UIApplication sharedApplication]delegate]).networkManager; //Instantiate class where that method is defined

    NSMutableDictionary *dictonary = [NSMutableDictionary dictionary];

    ...populate dictionary...

    [currentNetworkManager sendDictionary:dictionary toScript:@"script.php" completion:[^(id response)
     { //THIS iS THE LINE WHERE THE BAD ACCESS OCCURS

         NSLog(@"LoginViewController received response: %@", response);

     } copy]];
}

任何帮助将不胜感激！

Answer 1

该方法的completionBlock只接受一个参数，但您使用invoke方法调用该块。更可能的是，崩溃是因为运行时试图保留内存中应该是该参数的任何垃圾。

然而，您确实需要完全重构此代码。阻止主事件循环是不好的。 MEL上运行子runloop甚至更糟;它改变了调度队列处理语义的工作方式，并可能导致病态性能或行为不良。

你应该转向一个真正的异步模型。如果在完成这些查询之前应用程序无法继续，那么请设置阻止进度的模式指示器。

为此，您将代码松散地构造为：

•将用户界面置于“loading ...”或其他一些模态状态

•使用完成处理程序

执行数据的异步请求

•在完成处理程序中，将“更新UI”请求分派给主队列

•在“更新用户界面”上，拆除您的模态“loading ....”用户界面并更新用户的显示

无需阻止主事件循环执行任何操作。

块执行时EXC_BAD_ACCESS

1 个答案: