Question

我正在尝试从我的应用发送电子邮件。发送电子邮件窗口打开时，未设置收件人和正文。每当我尝试按任何字段来编辑它们时，我的应用程序崩溃并给我这个错误：

***断言失败 - [UIKeyboardTaskQueue waituntilalltasksarefinished]，/sourcuecache / UIKIt_Sim / UIKit-3318.16.14 / KeyTothQaskue.m：374 由于未捕获的异常终止应用程序＆＃39; NSInternalInconsistencyException＆＃39;，原因：＆＃39;仅在主线程上运行！

我查看了电子邮件教程，但无法找到我做错的事情。代码已添加供参考：

if ([MFMailComposeViewController canSendMail]) {
    // Get current date/time
    NSDate *date = picker.date;
    MFMailComposeViewController *mailer = [[MFMailComposeViewController alloc]init];
    mailer.mailComposeDelegate = self;
    mailer.modalPresentationStyle = UIModalPresentationCurrentContext;
    // Set title
    NSDateFormatter *dateFmt = [[NSDateFormatter alloc] init];
    [dateFmt setDateStyle:NSDateFormatterMediumStyle];
    [mailer setSubject:[NSString stringWithFormat:@"test email: sent on %@", [dateFmt stringFromDate:date]]];
    // Set recipient
    [mailer setToRecipients:@[@"testingEmail@example.com"]];
    // Set attachment
    CGRect r = CGRectMake(0, 0, 200, 200);
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
        UIGraphicsBeginImageContextWithOptions(r.size, NO, [UIScreen mainScreen].scale);
    else
        UIGraphicsBeginImageContext(r.size);

    CGContextRef c = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(UIGraphicsGetCurrentContext(), - mapview.center.x + r.size.width / 2.f, - mapview.center.y + r.size.height / 2.f);
    [mapholder.layer renderInContext:c];
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    NSData *imageData = UIImagePNGRepresentation(img);
    [mailer addAttachmentData:imageData mimeType:@"image/png" fileName:@"map"];
    // Set email body
    [dateFmt setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    CLLocationCoordinate2D loc = mapview.centerCoordinate;
    NSString *emailBody = [NSString stringWithFormat:@"BRO it is Time: %@\n Location: %f,%f", [dateFmt stringFromDate:date], loc.latitude, loc.longitude];
    [mailer setMessageBody:emailBody isHTML:NO];
    [self presentViewController:mailer animated:YES completion:nil];
}

和

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

Answer 1

你的例外说，原因：＆＃39;只在主线程上运行

使用以下命令检查代码是否在后台队列上运行：

NSLog(@"%@",[NSOperationQueue currentQueue]);

它应该在主队列中运行。如果没有尝试将代码包装在：

dispatch_async(dispatch_get_main_queue(), ^{
   ...
});

Answer 2

您无法在后台线程上显示UI。通常，您不应该对后台线程执行任何UIKit工作。通过在后台线程上调用像（UIImagePNGRepresentation）这样的重型映像API，您处于正确的轨道上。完成创建屏幕截图等后，需要调度到主队列以显示邮件视图控制器。

// Create mail composer with screenshots etc
// ...

// Now present mail composer on "MAIN" thread
dispatch_async(dispatch_get_main_queue(), ^{
    [self presentViewController:mailer animated:YES completion:nil];
}

MFMailComposeViewController无法正常工作

2 个答案: