MFMailComposeViewController - iPad

Question

我已经设置了一个MFMailComposeViewController，它在iPhone上工作得很好，但是在iPad上它崩溃了，它说：

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present a nil modal view controller on target...

那么为什么这会创建一个nil模式视图呢？

    MFMailComposeViewController *message = [[MFMailComposeViewController alloc] init];
    [message setMessageBody:@"My message here"  isHTML:NO];
    [message setToRecipients:[NSArray arrayWithObject:@"my@domain.com"]];
    [message setSubject:@"Request Info"];
    message.mailComposeDelegate = self;
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)
        message.modalPresentationStyle = UIModalPresentationFormSheet;
    [self presentModalViewController:message animated:YES];
    [message release];

有什么想法吗？

Answer 1

像MFMailComposeViewController这样的nil不是出于某种原因而创建的，因此具有Loo的价值。在演示之前检查它是否为nil (尽管此解决方法不能回答此处出现问题的原因...)。

在尝试使用+canSendMail方法创建和呈现邮件之前，您还应该检查邮件编写器是否可以发送邮件(它将返回NO，例如，如果设备上没有设置邮件帐户)：

 if ([MFMailComposeViewController canSendMail]){
    // Create and show composer
 }
 else{
   // Show some error message here
 }

Answer 2

在创建MFMailComposerViewController对象之前，您必须放入check canSendMail，查看来自MFMailComposeViewController.h类的以下注释：

/*!
@method     canSendMail
@abstract   Returns <tt>YES</tt> if the user has set up the device for sending email.
@discussion The client may continue to set the recipients and content if the return value was <tt>YES</tt>.  If <tt>NO</tt>
            was the result, the client has a couple options.  It may choose to simply notify the user of the inability to
            send mail, or it may issue a "mailto" URL via <tt>-[UIApplication openURL:]</tt>.
*/

+ (BOOL)canSendMail __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_0);

在您的设备设置为发送邮件之前，您的对象不会被初始化。

Answer 3

if ([MFMailComposeViewController   canSendMail]){
    //execute  your    code 
else{
    UIAlertView *anAlert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"No mail account setup on device" delegate:self cancelButtonTitle:nil otherButtonTitles:nil];     
    [anAlert addButtonWithTitle:@"OK"];
    [anAlert show];
}

如果您收到警报，请在手机上配置您的邮件帐户。