ios - NSInvalidArgumentException'，原因 : 'Application tried to present a nil modal view controller on target

Question

我使用 Xcode 7.3 beta 3 创建了一封电子邮件。我从 appcoda 获取代码

- (IBAction)showEmail:(id)sender {
    // Email Subject
    NSString *emailTitle = @"Test Email";
    // Email Content
    NSString *messageBody = @"iOS programming is so fun!";
    // To address
    NSArray *toRecipents = [NSArray arrayWithObject:@"support@appcoda.com"];

    MFMailComposeViewController *mc = [[MFMailComposeViewController alloc] init];
    mc.mailComposeDelegate = self;
    [mc setSubject:emailTitle];
    [mc setMessageBody:messageBody isHTML:NO];
    [mc setToRecipients:toRecipents];

    // Present mail view controller on screen
    [self presentViewController:mc animated:YES completion:NULL];

}

- (void) mailComposeController:(MFMailComposeViewController *)controller didFinishWithResult:(MFMailComposeResult)result error:(NSError *)error
{
    switch (result)
    {
        case MFMailComposeResultCancelled:
            NSLog(@"Mail cancelled");
            break;
        case MFMailComposeResultSaved:
            NSLog(@"Mail saved");
            break;
        case MFMailComposeResultSent:
            NSLog(@"Mail sent");
            break;
        case MFMailComposeResultFailed:
            NSLog(@"Mail sent failure: %@", [error localizedDescription]);
            break;
        default:
            break;
    }

    // Close the Mail Interface
    [self dismissViewControllerAnimated:YES completion:NULL];
}

但在 iPhone 上运行应用程序后，它给了我一个错误(如下所示)

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present a nil modal view controller on target .'* First throw call stack:()libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

NSInvalidArgumentException', reason: 'Application tried to present a nil modal view controller on target -- It means you try to implement the nil objcet on target check once if it is nil or not

MFMailComposeViewController *mc = [[MFMailComposeViewController alloc] init];
if (!mc) {  
  //When the device has not added mailViewController mail account is empty , the following present view controller causes the program to crash here
NSLog(@"no email accounts are set up in your device");  
return;  
} 

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