问iOS 4短信编写器不能正常工作

EN

BOOL canText = [MFMessageComposeViewController canSendText];

if(canText){
    MFMessageComposeViewController * smsViewController = [[MFMessageComposeViewController alloc] init];
    if(smsViewController){

        smsViewController.body = @"test message";
        smsViewController.messageComposeDelegate = self;

        [self presentModalViewController:smsViewController animated:YES];
        [smsViewController release];

    }else{
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"SMS" 
                                                        message:@"Your cannot send SMS on this device." 
                                                       delegate:nil 
                                              cancelButtonTitle:@"ok" 
                                              otherButtonTitles:nil];

        [alert show];
        [alert release];

    }
}else{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"SMS" 
                                                    message:@"Your cannot send SMS on this device." 
                                                   delegate:nil 
                                          cancelButtonTitle:@"ok" 
                                          otherButtonTitles:nil];

    [alert show];
    [alert release];

}