Using PerformSelector with @selector in MonoTouch

Question

I am trying to convert the following iOS code into MonoTouch and cannot figure out the proper conversion for the @selector(removebar) code. Can anyone provide guidance about the best way to handle @selector (since I've come across that in other places as well):

- (void)keyboardWillShow:(NSNotification *)note {
[self performSelector:@selector(removeBar) withObject:nil afterDelay:0];
}

My C# code is:

NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification,
              notify => this.PerformSelector(...stuck...);

I am basically trying to hide the Prev/Next buttons that show on the keyboard.

Thanks in advance for any help.

Answer 1

NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification, removeBar);

where removeBar is a method defined elsewhere.

void removeBar (NSNotification notification)
{
    //Do whatever you want here
}

Or, if you prefer using a lambda:

NSNotificationCenter.DefaultCenter.AddObserver (UIKeyboard.WillShowNotification, 
                                                notify => { 
                                                    /* Do your stuffs here */
                                                });

Answer 2

You have to take into account that:

[self performSelector:@selector(removeBar) withObject:nil afterDelay:0];

it's exactly the same that

[self removeBar];

The call to performSelector is just a method call using reflection. So what you really need to translate to C# is this code:

- (void)keyboardWillShow:(NSNotification *)note {
    [self removeBar];
}

And I guess that also the notification subscription, that sums up to this code:

protected virtual void RegisterForKeyboardNotifications()
{
    NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification, OnKeyboardNotification);
    NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification, OnKeyboardNotification);
}

private void OnKeyboardNotification (NSNotification notification)
{
    var keyboardVisible = notification.Name == UIKeyboard.WillShowNotification;

    if (keyboardVisible) 
    {
        // Hide the bar
    }
    else
    {
        // Show the bar again
    }
}

You usually want to call RegisterForKeyboardNotifications on ViewDidLoad.

Cheers!

Answer 3

Stephane shows one way you can use our improved bindings to convert that.

Let me share an even better one. What you are looking for is a keyboard notification, which we conveniently provide strong types for, and will make your life a lot easier:

http://iosapi.xamarin.com/?link=M%3aMonoTouch.UIKit.UIKeyboard%2bNotifications.ObserveWillShow

It contains a full sample that shows you how to access the strongly typed data that is provided for your notification as well.