Iphone 单击uiBarButton时出错

单击uiBarButton时，会发生NSInvalidArgumentException，我的代码如下：

-(IBAction) sendSms:(id)sender {

        MFMessageComposeViewController *picker = [[MFMessageComposeViewController alloc] init];
        picker.messageComposeDelegate = self;

        picker.recipients = [NSArray arrayWithObject:@"1234567890"];  
        picker.body = @"Help me";

        [self presentModalViewController:picker animated:YES];
        [picker release];
}

- (void)messageComposeViewController:(MFMessageComposeViewController *)controller didFinishWithResult:(MessageComposeResult)result {
    NSString *message = [[NSString alloc] init];
    switch(result) {
        case MessageComposeResultCancelled:
            message = [[NSString alloc] initWithFormat:@"Result: cancelled"];
            NSLog(@"Result: canceled");
            break;
        case MessageComposeResultSent:
            message = [[NSString alloc] initWithFormat:@"Result: sent"];
            NSLog(@"Result: sent");
            break;
        case MessageComposeResultFailed:
            message = [[NSString alloc] initWithFormat:@"Result: failed"];
            NSLog(@"Result: failed");
            break;
        default:
            message = [[NSString alloc] initWithFormat:@"Result: not sent"];
            NSLog(@"Result: not sent");
            break;
    }
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Message Status" message:message delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert show];
    [alert release];
    [message release];

    [self dismissModalViewControllerAnimated:YES];

}

错误显示目标上的nil模态视图控制器。请告诉我我的错误，我已经将uibarButton的操作与interface builder中的IBAaction正确链接。请尽快帮助我。提前谢谢。

请检查此项

MFMessageComposeViewController对象（选择器）未正确初始化。

---

此处列出了无法初始化的条件。

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