keyboard添加down按钮

self.textView.inputAccessoryView = [self addToolbar];
- (UIToolbar *)addToolbar
{
    UIToolbar *toolbar = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, CGRectGetWidth(self.view.frame), 35)];
    toolbar.tintColor = [UIColor blueColor];
    toolbar.backgroundColor = [UIColor grayColor];
    UIBarButtonItem *nextButton = [[UIBarButtonItem alloc] initWithTitle:@"下一步" style:UIBarButtonItemStylePlain target:self action:@selector(nextTextField)];
    UIBarButtonItem *prevButton = [[UIBarButtonItem alloc] initWithTitle:@"上一步" style:UIBarButtonItemStylePlain target:self action:@selector(prevTextField)];
    UIBarButtonItem *space = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
    UIBarButtonItem *bar = [[UIBarButtonItem alloc] initWithTitle:@"完成" style:UIBarButtonItemStylePlain target:self action:@selector(textFieldDone)];
    toolbar.items = @[nextButton, prevButton, space, bar];
    return toolbar;
}