在数字键盘上添加button

//定义一个消息中心

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil]; //addObserver:注册一个观察员 name:消息名称

- (void)keyboardWillShow:(NSNotification *)note {

    // create custom button

    UIButton *doneButton = [UIButton buttonWithType:UIButtonTypeCustom];

    doneButton.frame = CGRectMake(0, 163, 106, 53);

    [doneButton setImage:[UIImage imageNamed:@"5.png"] forState:UIControlStateNormal];

    [doneButton addTarget:self action:@selector(addRadixPoint) forControlEvents:UIControlEventTouchUpInside];

  

    // locate keyboard view

    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];//返回应用程序window

    UIView* keyboard;

    for(int i=0; i<[tempWindow.subviews count]; i++) //遍历window上的所有subview

    {

        keyboard = [tempWindow.subviews objectAtIndex:i];

        // keyboard view found; add the custom button to it

        if([[keyboard description] hasPrefix:@"<UIKeyboard"] == YES)

        [keyboard addSubview:doneButton];

    }

}