MFMessageComposeViewController alloc returns nil

问题

In my application, MFMailComposeViewController works fine but creating a new instance of MFMessageComposeViewController fails.

Here is the code for both:

-( IBAction)sendSMS: (id)sender
{
 MFMessageComposeViewController *picker = [[[MFMessageComposeViewController alloc] init] autorelease];
 picker.messageComposeDelegate = self;

 NSArray *toRecipients = [NSArray arrayWithObject: cell.currentTitle ]; 

 picker.recipients = toRecipients;

 [self presentModalViewController:picker animated:YES];
}

-( IBAction)sendEmail: (id)sender
{
 MFMailComposeViewController *picker = [[[MFMailComposeViewController alloc] init] autorelease];
 picker.mailComposeDelegate = self;

 NSArray *toRecipients = [NSArray arrayWithObject: email.currentTitle ]; 

 [picker setToRecipients:toRecipients];

 [self presentModalViewController:picker animated:YES];
}

Its seemingly obvious that everything is linking correctly because the email view controller works fine. Is there something I am missing maybe configuration wise?

回答1:

Have you checked +[MFMessageComposeViewController canSendText]?

From the MFMessageComposeViewController Class Reference,

Before presenting a message composition view, call the canSendText class method to ensure that the user’s device is appropriately configured. Do not attempt to present a message composition view if the canSendText method returns NO. If SMS delivery isn’t available, you can notify the user or simply disable the SMS features in your application.

Starting in iOS 5, you can register to be notified of changes to the availability of text message sending by way of the MFMessageComposeViewControllerTextMessageAvailabilityDidChangeNotification notification.

Reasons it might be returning nil:

• Device isn't running iOS 4.
• Device is an iPod Touch/iPad without iMessage enabled.
• No SIM card? (The view now shows in iOS 6; the app is not notified of the message send failure.)
• "Device" is actually the simulator. (Perhaps this works in iOS 6 too.)

Similarly, [[MFMailComposeViewController alloc] init] returns nil when no mail accounts are enabled (you can quickly test this by disabling accounts in Settings), but also shows a "No mail accounts configured" alert for you. MFMessageComposeViewController does not do this.

来源：https://stackoverflow.com/questions/3498531/mfmessagecomposeviewcontroller-alloc-returns-nil