iPad模擬器出錯，但iPhone出現錯誤

Question

我有一個segue，我喜歡這樣：

[self performSegueWithIdentifier:@"PlanToBusiness" sender:self];

它適用於iPhone而不適用於iPad。 我所做的是遠程調用服務器，當服務器響應正確返回時，我嘗試將用戶帶到具有該segue的新頁面。

它適用於iPhone模擬器，但不適用於iPad（兩者的識別字符串相同），並且在iPad上它會因此錯誤而崩潰：

bool _WebTryThreadLock(bool), 0x68f9cb0: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now...
1   WebThreadLock
2   -[UITextRangeImpl isEmpty]
3   -[UITextRange(UITextSelectionAdditions) _isCaret]
4   -[UITextSelectionView setCaretBlinks:]
5   -[UIKeyboardImpl setCaretBlinks:]
6   -[UIKeyboardImpl setDelegate:force:]
7   -[UIKeyboardImpl setDelegate:]
8   -[UIPeripheralHost(UIKitInternal) _reloadInputViewsForResponder:]
9   -[UINavigationController navigationTransitionView:didStartTransition:]
10  -[UINavigationTransitionView transition:fromView:toView:]
11  -[UINavigationTransitionView transition:toView:]
12  -[UINavigationController _startTransition:fromViewController:toViewController:]
13  -[UINavigationController _startDeferredTransitionIfNeeded]
14  -[UINavigationController pushViewController:transition:forceImmediate:]
15  -[UINavigationController pushViewController:animated:]
16  -[UIStoryboardPushSegue perform]
17  -[UIStoryboardSegueTemplate perform:]
18  -[UIViewController performSegueWithIdentifier:sender:]
19  __41-[PlanBusinessController submitBusiness:]_block_invoke_0
20  __block_global_0
21  -[NSBlockOperation main]
22  -[__NSOperationInternal start]
23  -[NSOperation start]
24  __block_global_6
25  _dispatch_call_block_and_release
26  _dispatch_worker_thread2
27  _pthread_wqthread
28  start_wqthread

我也不習慣讀取Obective-C堆棧跟蹤，因此我很難確定問題所在。

我是這樣做的：

- (IBAction)submitBusiness:(id)sender 
{    
     // Make a url to send

     NSURL *url = [NSURL URLWithString:full_encoded_url_string];
     NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];

        // ***************
        // TODO: ok I dont really understand what this is
        NSOperationQueue *queue = [[NSOperationQueue alloc] init];
        // **************

        [NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
         {   
                         // I took out a lot of the logic code that is not needed

                         [self performSegueWithIdentifier:@"PlanToBusiness" sender:self];
         }];
    }
}

Answer 1

當觸摸UI的方法（例如執行segue時），確保從主線程調用該代碼非常重要。 最簡單的方法是制作一個這樣的方法：

- (void)performPlanToBusinessSegueOnMainThread
{
    [self performSegueWithIdentifier:@"PlanToBusiness" sender:self];
}

然后，您可以在完成的塊中調用此方法，如下所示：

[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
 {   
     // I took out a lot of the logic code that is not needed

     [self performSelectorOnMainThread:@selector(performPlanToBusinessSegueOnMainThread) 
                            withObject:nil 
                         waitUntilDone:YES];
 }];

這有點迂回，但它應該修復你的異常。 如果我們可以在performSelectorOnMainThread方法中調用performSegueWithIdentifier會更好，但它有太多的參數。