How to specify notificationSender? (Cocoa Touch)

Question

All of the examples I can find of setting up a notification look like this:

[nc addObserver:self selector:@selector(keyboardWillShow:) name: UIKeyboardWillShowNotification object:nil];

where object is always being set to nil. object is the notificationSender, which is defined thusly in the documentation:

"The object whose notifications the observer wants to receive; that is, only notifications sent by this sender are delivered to the observer. When nil, the notification center doesn’t use a notification’s sender to decide whether to deliver it to the observer."

I want to receive the keyboard notification only for one particular text view, so I want to tell addObserver that, but I don't know what to give it for the object. I tried the outlet variable that's bound to the text view I'm interested in, but that just resulted in my getting no notifications at all.

Any suggestions?

Answer 1

In this case you can not get the notification only for one particular text view, as the docu for UIKeyboardWillShowNotification says "The notification object is nil.".

You have to check in your keyboardWillShow impl if your particular text view isFirstResponder.

Answer 2

The UIKeyboardWillShowNotification is coming from your window instance, and for all intents and purposes is a "system" notification. The keyboard is either showing or not showing, it's not really something that is tied to a specific control.

If you want to do something when a user enters a specific text field, you should probably control that in the text field's delegate instead.

Answer 3

I had two competing needs - I had to use the keyboard notification because I needed to get the keyboard height, which appears to be only available that way, but I also needed to know which text view I was in, which meant also using the textViewDidBeginEditing delegate. After much messing around I finally resorted to getting the keyboard height in the notification method and storing it in an instance variable, which was then available to use in the delegate method (I need to scroll the view up so the bottom text view is not mostly hidden under they keyboard when they start typing). A bit inelegant, but it works.

Thanks for the pointers!