我也遇到了这个问题并找到了解决方案。

I also had this problem and found the solution.

下面的代码适用于iOS 8.0以及以下版本。

Below is the code which will work for iOS 8.0 and also for below versions.

我在iOS上测试过它7和8.0（Xcode版本6.0.1）

I have tested it on iOS 7 and 8.0 (Xcode Version 6.0.1)

- (void)addButtonToKeyboard
{
    // create custom button
    self.doneButton = [UIButton buttonWithType:UIButtonTypeCustom];
    self.doneButton.frame = CGRectMake(0, 163+44, 106, 53);
    self.doneButton.adjustsImageWhenHighlighted = NO;
    [self.doneButton setTag:67123];
    [self.doneButton setImage:[UIImage imageNamed:@"doneup1.png"] forState:UIControlStateNormal];
    [self.doneButton setImage:[UIImage imageNamed:@"donedown1.png"] forState:UIControlStateHighlighted];

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

    // locate keyboard view
    int windowCount = [[[UIApplication sharedApplication] windows] count];
    if (windowCount < 2) {
        return;
    }

    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];
    UIView* keyboard;

    for(int i = 0 ; i < [tempWindow.subviews count] ; i++)
    {
        keyboard = [tempWindow.subviews objectAtIndex:i];
        // keyboard found, add the button

        if([[keyboard description] hasPrefix:@"<UIPeripheralHost"] == YES){
            UIButton* searchbtn = (UIButton*)[keyboard viewWithTag:67123];
            if (searchbtn == nil)//to avoid adding again and again as per my requirement (previous and next button on keyboard)
                [keyboard addSubview:self.doneButton];

        }//This code will work on iOS 8.0
        else if([[keyboard description] hasPrefix:@"<UIInputSetContainerView"] == YES){

            for(int i = 0 ; i < [keyboard.subviews count] ; i++)
            {
                UIView* hostkeyboard = [keyboard.subviews objectAtIndex:i];

                if([[hostkeyboard description] hasPrefix:@"<UIInputSetHost"] == YES){
                    UIButton* donebtn = (UIButton*)[hostkeyboard viewWithTag:67123];
                    if (donebtn == nil)//to avoid adding again and again as per my requirement (previous and next button on keyboard)
                        [hostkeyboard addSubview:self.doneButton];
                }
            }
        }
    }
}

>

>

    -(void) removedSearchButtonFromKeypad{

    int windowCount = [[[UIApplication sharedApplication] windows] count];
    if (windowCount < 2) {
        return;
    }

    UIWindow* tempWindow = [[[UIApplication sharedApplication] windows] objectAtIndex:1];

    for(int i = 0 ; i < [tempWindow.subviews count] ; i++)
    {
        UIView* keyboard = [tempWindow.subviews objectAtIndex:i];

        if([[keyboard description] hasPrefix:@"<UIPeripheralHost"] == YES){
            [self removeButton:keyboard];

        }else if([[keyboard description] hasPrefix:@"<UIInputSetContainerView"] == YES){

            for(int i = 0 ; i < [keyboard.subviews count] ; i++)
            {
                UIView* hostkeyboard = [keyboard.subviews objectAtIndex:i];

                if([[hostkeyboard description] hasPrefix:@"<UIInputSetHost"] == YES){
                    [self removeButton:hostkeyboard];
                }
            }
        }
    }
}


-(void) removeButton:(UIView*)keypadView{
    UIButton* donebtn = (UIButton*)[keypadView viewWithTag:67123];
    if(donebtn){
        [donebtn removeFromSuperview];
        donebtn = nil;
    }
}

希望这有帮助。

Hope this helps.