Handle keyboard show/hide in Xamarin.iOS.

keyboardIOS.cs

NSObject keyboardShowObserver;
NSObject keyboardHideObserver;
public override void ViewWillAppear(bool animated) {
    base.ViewWillAppear(animated);

    keyboardShowObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification, (notification) => {
        NSValue nsKeyboardBounds = (NSValue)notification.UserInfo.ObjectForKey(UIKeyboard.BoundsUserInfoKey);
        RectangleF keyboardBounds = nsKeyboardBounds.RectangleFValue;
        float height = View.Bounds.Height - keyboardBounds.Height;
        if (NavigationController != null && NavigationController.TabBarController != null && NavigationController.TabBarController.TabBar != null) {
            // Re-add tab bar height since it is hidden under keyboard but still excluded from View.Bounds.Height.
            height += NavigationController.TabBarController.TabBar.Frame.Height;
        }
        
        someScrollView.Frame = new RectangleF(someScrollView.Frame.Location, new SizeF(View.Bounds.Width, height));
    });
    keyboardHideObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification, (notification) => {
        UIApplication.EnsureUIThread();
        
        someScrollView.Frame = new RectangleF(someScrollView.Frame.Location, View.Bounds.Size);
    });
}
public override void ViewDidDisappear(bool animated) {
    base.ViewDidDisappear(animated);
    if (keyboardShowObserver != null) {
        NSNotificationCenter.DefaultCenter.RemoveObserver(keyboardShowObserver);
    }
    if (keyboardHideObserver != null) {
        NSNotificationCenter.DefaultCenter.RemoveObserver(keyboardHideObserver);
    }
}