当键盘滑入键盘时，如何禁用NAV栏的“完成”按钮？

Question

我相信我无法禁用它，因为我无法访问 UIBarButttonItem 以编程方式
（使用ViewWithTag或 rightBarButtonItem).

有任何建议（添加没有IB的界面的简短）？
作为测试，我还尝试通过编程添加一个按钮（在NAV栏的左侧），但没有在NAV栏中显示。

相关代码（在 MyEditorViewControler.m):

    - (void)textFieldDidBeginEditing:(UITextField *)sender { //successfully executes when keyboard slides in

        UINavigationItem *item = self.navigationItem; //item  = 0x6420e0  OK.  (value at debugger breakpoints)
        UIBarButtonItem *doneButton4    = (UIBarButtonItem *) [self.view viewWithTag:44]; //doneButton4 = 0x0,  not OK.
        doneButton4.enabled = NO; 
    }
    - (void)textFieldDidEndEditing:(UITextField *)sender {  //successfully executes when keyboard  slides out.  
        ...
        UIButton* doneButton = (UIButton *)[self.view viewWithTag:44]; //Attempt to re-enable button.
        doneButton.enabled = YES;
    }
    - (void)viewDidLoad {   //Attempt to programmatically add a *left* button to the nav bar. Result: Button does not display in nav bar.
        .... 
        UIBarButtonItem *leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(done)];
        self.navigationItem.leftBarButtonItem = leftBarButtonItem;
        [leftBarButtonItem release];
    }

细节
我认为这是一个常见的情况，因为那个完成按钮：
a）是 UIBarButttonItem 从IB库中添加到带有一些滚动视图中的导航栏 UITextField's.
b）行为如预期的（保存用户输入的数据等），
除了出现键盘时未被禁用。
c）IB> Inspector> BAR按钮项属性显示：
标识符=完成
标签= 44
class = UIBarButtonItem

Answer 1

您可以收听通知（UIKeyboardWillShowNotification）键盘滑动时发布：

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

然后实现 -keyboardWillShow:.

-(void)keyboardWillShow {
    UIButton *button = self.navigationItem.leftBarButtonItem;
    button.enabled = NO;
}

要再次重新确定按钮，请对 UIKeyboardDidHideNotification

Answer 2

你应该只使用

UIBarButtonItem *doneButton = self.navigationItem.leftBarButtonItem; 
doneButton.enabled = YES;

//Both of these should work, you shouldn't need any type of IBOutlets for this

UINavigationItem *item = self.navigationItem;
UIBarButtonItem *doneButton = item.leftBarButtonItem;