How to handle NSFetchedResultsController fetch errors?
This is from the Apple sample code:
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"?
Any 开发者_运维技巧suggestions would be appreciated, Fabian
Well, apparently nobody has another (better?) solution, so here is my approach:
In my AppController I added a instance variable errorString
and this method:
- (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()
:
- (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()
):
- (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];
}
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