应用程序试图在 iOS 10 的目标上呈现一个 nil 模式视图控制器？

Question

当我点击我的邮件按钮时，我正在我的应用程序中实现 MFMailComposeViewController 我收到以下错误。

应用程序试图在目标强文本上呈现一个零模式视图控制器

这是我的代码：

    NSString *iOSVersion = [[UIDevice currentDevice] systemVersion];
    NSString * version = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleShortVersionString"];

    NSString * build = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"];

    mailComposer = [[MFMailComposeViewController alloc]init];
    mailComposer.navigationBar.tintColor = [UIColor blackColor];
    [mailComposer.navigationBar setTitleTextAttributes:
     @{NSForegroundColorAttributeName:[UIColor blackColor]}];
    mailComposer.mailComposeDelegate = self;

    [mailComposer setSubject:@"Co - Contact Us"];

    [mailComposer setToRecipients:@[@"contact@co.org"]];
    NSString *supportText = @"Enter your comment here:\n\n\n\n\n";
    supportText = [supportText stringByAppendingString:[NSString stringWithFormat:@"iOS Version: %@\nCorner Version:%@\nBuild:%@\n\n",iOSVersion,version, build]];
    [mailComposer setMessageBody:supportText isHTML:NO];

    [self presentViewController:mailComposer animated:YES completion:nil];

我的代码有什么问题。请帮忙

Answer 1

如果设备没有配置邮件或使用模拟器可能会导致崩溃或异常。

mailComposer = [[MFMailComposeViewController alloc] init];

上面的代码行可能会导致问题。在模拟器中初始化方法可能返回NULL 或nil。

所以，在呈现模态视图控制器之前检查canSendMail：

喜欢，

    NSString *iOSVersion = [[UIDevice currentDevice] systemVersion];
    NSString * version = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleShortVersionString"];

    NSString * build = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"CFBundleVersion"];

    mailComposer = [[MFMailComposeViewController alloc]init];

    if ([MFMailComposeViewController canSendMail] && mailComposer) {

       mailComposer.navigationBar.tintColor = [UIColor blackColor];
       [mailComposer.navigationBar setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor blackColor]}];
       mailComposer.mailComposeDelegate = self;

       [mailComposer setSubject:@"Corner - Contact Us"];

       [mailComposer setToRecipients:@[@"contact@corner.org"]];
       NSString *supportText = @"Enter your comment here:\n\n\n\n\n";
       supportText = [supportText stringByAppendingString:[NSString stringWithFormat:@"iOS Version: %@\nCorner Version:%@\nBuild:%@\n\n",iOSVersion,version, build]];
       [mailComposer setMessageBody:supportText isHTML:NO];

      [self presentViewController:mailComposer animated:YES completion:nil];
}