在UIToolBar上使用Done按钮关闭UIPickerView

// 创建UIToolBar对象
UIToolbar *toolbar = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, 44)];

// 创建UIBarButtonItem对象
UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(doneButtonTapped:)];

// 将UIBarButtonItem设置为UIToolBar的右侧按钮
UIBarButtonItem *flexibleSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
[toolbar setItems:@[flexibleSpace, doneButton]];

// 将UIToolBar添加到UIPickerView的顶部
yourPickerView.inputAccessoryView = toolbar;

// Done按钮的点击事件
- (void)doneButtonTapped:(id)sender {
    // 关闭UIPickerView
    [yourPickerView resignFirstResponder];
}