button item lost when hide and unhide toolbar

i dont know, why the button are disappear after the toolbar set to hide and unhide. how can i fix it?

setup a button code

-(void)viewDidAppear:(BOOL)animated {
    //NSLog(@"viewDidAppear ");

    [self becomeFirstResponder];
    //Create a button
    UIBarButtonItem *back = [[UIBarButtonItem alloc] 
                        initWithBarButtonSystemItem:UIBarButtonSystemItemRewind 
                target:self action:@selector(goback:)];

    UIBarButtonItem *fixspace1 = [[UIBarButtonItem alloc] 
                                 initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace 
                                 target:self action:nil];

    UIBarButtonItem *next = [[UIBarButtonItem alloc] 
                             initWithBarButtonSystemItem:UIBarButtonSystemItemFastForward 
                             target:self action:@selector(gofwd:)];
    UIBarButtonItem *stop = [[UIBarButtonItem alloc] 
                             initWithBarButtonSystemItem:UIBarButtonSystemItemStop 
                             target:self action:@selector(stopload:)];

    UIBarButtonItem *refresh = [[UIBarButtonItem alloc] 
                             initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh 
                             target:self action:@selector(refreshWeb:)];


    [self.navigationController.toolbar setItems:[NSArray arrayWithObjects:fixspace1, back, fixspace1, stop, fixspace1, next, fixspace1, nil] animated:YES];
    [self.navigationItem setRightB开发者_开发知识库arButtonItem:refresh animated:YES];

    [self.navigationController.view addSubview:self.navigationController.toolbar];

    [stop release];
    [next release];
    [back release];
    [refresh release];
    [fixspace1 release];
}

and i setup my button at this method

-(void)viewDidAppear:(BOOL)animated 

this code use for hide toolbar

    [self.navigationController setNavigationBarHidden:YES animated:YES];
    [[UIApplication sharedApplication] setStatusBarHidden:YES animated:YES];
    [self.navigationController setToolbarHidden:YES animated:YES];

The documented method for setting toolbar items is via the toolbarItems property of the view controller. The same UINavigationController Reference also lists the toolbar property as read-only and specifically warns

You should not modify the UIToolbar object directly.

Therefore, try changing

[self.navigationController.toolbar setItems:[NSArray arrayWithObjects:fixspace1, back, fixspace1, stop, fixspace1, next, fixspace1, nil] animated:YES];

to

[self setToolbarItems:[NSArray arrayWithObjects:fixspace1, back, fixspace1, stop, fixspace1, next, fixspace1, nil] animated:YES];

Seeing no better answers, I'll promote my earlier comment. Try taking out this line:

[self.navigationController.view addSubview:self.navigationController.toolbar];

I haven't experimented with anything like that but it looks wrong and very much against the iPhone SDK philosophy. If the controller object already has a pointer to the toolbar, why would you need to add it to the view? If that's the right place for it, the controller object would do that itself.

I doub't that you should release your toolbar buttons immediately after adding them to the toolbar. You should save them in instance variables and release them in your dealloc.