如何处理NSFetchedResultsController获取错误？

This is from the Apple sample code:

这是来自Apple示例代码：

if (![fetchedResultsController_ performFetch:&error]) {
     /*
      Replace this implementation with code to handle the error appropriately.
      ...
      If it is not possible to recover from the error, ...
      */
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

I am wondering whether it is really necessary to always terminate the app? How could you "replace this implementation with code to handle the error appropriately"? And how would you "recover from the error"?

我想知道是否真的有必要总是终止应用程序？你怎么能“用代码替换这个实现来适当地处理错误”？你将如何“从错误中恢复”？

Any suggestions would be appreciated, F*

任何建议都将受到赞赏，F*

1 个解决方案

#1

Well, apparently nobody has another (better?) solution, so here is my approach:

好吧，显然没有人有另一个（更好的？）解决方案，所以这是我的方法：

In my AppController I added a instance variable errorString and this method:

在我的AppController中，我添加了一个实例变量errorString和这个方法：

- (void)presentCoreDataError:(NSError *)error
                    withText:(NSString *)text
{
    NSMutableString *localErrorString = [[NSMutableString alloc] init];

    [localErrorString appendFormat:@"Failed to %@: %@", text, [error localizedDescription]];

    NSArray* detailedErrors = [[error userInfo] objectForKey:NSDetailedErrorsKey];
    if(detailedErrors != nil && [detailedErrors count] > 0) {
        for(NSError* detailedError in detailedErrors) {
            [localErrorString appendFormat:@"- Detail: %@", [detailedError userInfo]];
        }
    } else {
        [localErrorString appendFormat:@"- %@", [error userInfo]];
    }

    UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"Failed to %@", text]
                                                     message:@"Please send a report to the developer."
                                                    delegate:self
                                           cancelButtonTitle:@"Cancel"
                                           otherButtonTitles:@"Send Report", nil] autorelease];
    [alert show];

    self.errorString = localErrorString;
    [localErrorString release];
}

The UIAlertView delegate displays an MFMailComposeViewController with the errorString in the cool courier font :) if "Send Report" is tapped. Otherwise it calls abort():

如果点击“发送报告”，则UIAlertView委托以冷却快递字体:)显示带有errorString的MFMailComposeViewController。否则它调用abort（）：

- (void) alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    if (buttonIndex == 1) {     // Send Report
        MFMailComposeViewController *picker = [[MFMailComposeViewController alloc] init];
        picker.mailComposeDelegate = self;
        NSArray *toRecipients = [NSArray arrayWithObject:@"first@example.com"];
        [picker setToRecipients:toRecipients];
        [picker setSubject:@"Error Report"];
        [picker setMessageBody:[NSString stringWithFormat:@"The application crashed with the following error:<br><br><FONT FACE=%@> %@ </FONT>", 
                                @"courier", errorString] 
                        isHTML:YES];

        [navigationController presentModalViewController:picker animated:YES];
        [picker release];
    } else {
        abort();
    }
}

And the MFMailComposeViewControllerDelegate displays a second UIAlertView with only one button (obviously the button has index 0, so it will call abort()):

并且MFMailComposeViewControllerDelegate只显示一个带有一个按钮的UIAlertView（显然按钮的索引为0，因此它将调用abort（））：

- (void)mailComposeController:(MFMailComposeViewController *)controller
          didFinishWithResult:(MFMailComposeResult)result
                        error:(NSError *)error
{
    [navigationController dismissModalViewControllerAnimated:YES];

    NSMutableString *messageString = [[NSMutableString alloc] init];

    if (result == MFMailComposeResultSent) {
        [messageString appendFormat:@"Thanks! "];
    }

    [messageString appendFormat:@"The application has to quit now."];
    UIAlertView *abortAlert = [[[UIAlertView alloc] initWithTitle:nil
                                                          message:messageString
                                                         delegate:self
                                                cancelButtonTitle:@"OK"
                                                otherButtonTitles:nil] autorelease];

    [abortAlert show];

    [messageString release];
}

#1