ios - 显示消息会导致崩溃吗？答案

【问题标题】：ios - can showing a message cause a crash?ios - 显示消息会导致崩溃吗？
【发布时间】：2012-11-18 22:04:41
【问题描述】：

我有这个代码：

[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
 {         
     NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;

     if ( error != nil )
     {
         // Display a message to the screen.
         UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"There was a server error getting your business plan. We use a remote server to backup your work." 
                    message:@"Please make sure your phone is connected to the Internet. If the problem persists, please let us know about this." 
                delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];

         [message show];

但它在 NSUrlConnection 从服务器返回时执行。它在极少数情况下会造成崩溃。可能吗？这似乎是一段无害的代码。

谢谢！

【问题讨论】：

您的消息内容是从NSURLConnection 中提取的吗？
这段代码在哪里？它是否放置在NSURLConnectionDelegate 指定的委托方法中？如果是这样，问题就在于此。如果您可以发布更多示例代码，我们将更容易为您提供帮助。
@esqew 不，内容只是纯文本。
刚刚发布了一个更大的代码时钟。

标签： ios ios5 nsurlconnection

【解决方案1】：

NSURLConnection 是否在某个奇怪的线程上返回结果？我不知道，但我怀疑 UIAlertView 仅适用于 UI 线程，因为它从 UI 开始。

 (dispatch_async(dispatch_get_main_queue(), ^{ 
    UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"There was a server error getting your business plan. We use a remote server to backup your work." 
                message:@"Please make sure your phone is connected to the Internet. If the problem persists, please let us know about this." 
            delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];

     [message show];
 });)

抱歉，这里没有编译，可能有错别字。

【讨论】：

代码在 NSUrlConnection 调用后执行的块中。不建议在那里显示该消息吗？我应该如何正确地向用户展示内容？
对不起，这里写的不够小。看下一个答案！

【解决方案2】：

如果是进入条件块显示错误不是因为UIAlert，是因为NSURLConnection遇到了错误。我会将错误信息输出到控制台，以便您在遇到这些罕见情况时看到错误是什么，并使用 NSURLConnection 解决问题

【讨论】：

Crashalytics 提供了有关错误的额外信息：异常类型：SIGSEGVCode:SEGV_ACCERR
__36-[BusinessController viewDidAppear:]_block_invoke_0
但是我将如何重构代码以使其更安全且不会崩溃？
当它出错时，我会输出由localizedDescription 和localizedFailureReason 返回的字符串，如 NSError 类参考中所指定的，以深入了解 NSURLConnection 失败的原因。参考：developer.apple.com/library/mac/#documentation/Cocoa/Reference/…

【解决方案3】：

问题是，您没有在主线程中显示 alertView。所有与 UI 相关的代码都需要在主线程上工作。

当我在另一个线程上显示 alertView 时，我遇到了类似的崩溃。

您需要更改方法，例如：

[NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
 {         
     NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;

     if ( error != nil )
     {
         // Display a message to the screen.
        dispatch_async(dispatch_get_main_queue(), ^{

          UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"There was a server error getting your business plan. We use a remote server to backup your work." 
                    message:@"Please make sure your phone is connected to the Internet. If the problem persists, please let us know about this." 
                delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];

          [message show];
       });
     }
}

或将其更改为：

 [NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
 {         
     NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;

     if ( error != nil )
     {
         // Display a message to the screen.
          UIAlertView *message = [[UIAlertView alloc] initWithTitle:@"There was a server error getting your business plan. We use a remote server to backup your work." 
                    message:@"Please make sure your phone is connected to the Internet. If the problem persists, please let us know about this." 
                delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
         [message performSelectorOnMainThread:@selector(show) withObject:nil waitUntillDone:NO];

     }
}

【讨论】：