I'm trying to have a UIPickerView slide from the bottom of the screen (over the top of a tab bar) but can't seem to get it to show up. The actual code for the animation is coming from one of Apple's example code projects (DateCell). I'm calling this code from the first view controller (FirstViewController.m) under the tab bar controller.

- (IBAction)showModePicker:(id)sender {
if (self.modePicker.superview == nil) {
    [self.view.window addSubview:self.modePicker];

    // size up the picker view to our screen and compute the start/end frame origin for our slide up animation
    //
    // compute the start frame
    CGRect screenRect = [[UIScreen mainScreen] applicationFrame];
    CGSize pickerSize = [self.modePicker sizeThatFits:CGSizeZero];
    CGRect startRect = CGRectMake(0.0, screenRect.origin.y + screenRect.size.height, pickerSize.width, pickerSize.height);
    self.modePicker.frame = startRect;

    // compute the end frame
    CGRect pickerRect = CGRectMake(0.0, screenRect.origin.y + screenRect.size.height - pickerSize.height, pickerSize.width, pickerSize.height);

    // start the slide up animation
    [UIView beginAnimations:nil context:NULL];
    [UIView setAnimationDuration:0.3];

    // we need to perform some post operations after the animation is complete
    [UIView setAnimationDelegate:self];

    self.modePicker.frame = pickerRect;

    // shrink the vertical size to make room for the picker
    CGRect newFrame = self.view.frame;
    newFrame.size.height -= self.modePicker.frame.size.height;
    self.view.frame = newFrame;
    [UIView commitAnimations];

    // add the "Done" button to the nav bar
    self.navigationItem.rightBarButtonItem = self.doneButton;
}}

Whenever this action fires via a UIBarButtonItem that lives in a UINavigationBar (which is all under the FirstViewController) nothing happens. Can anyone please offer some advice?