IOS:Create subMenu using UIMenuItemController inside a UIWebView

Question

I would like the behaviour is that:

When I click on my custom UIMenuItem, it would show another list of UIMenuItems to choose. I have implemented in that way.

@implementation CustomUIWebView{
    BOOL clickedShowSubMenu;
    NSArray *mainMenuItems;
    NSArray *subMenuItems;
}

-(id)initWithCoder:(NSCoder *)aDecoder{
    self = [super initWithCoder:aDecoder];
    if(self){
        UIMenuController *mc = [UIMenuController sharedMenuController];

        UIMenuItem *testSubMenu = [[UIMenuItem alloc] initWithTitle:@"TestSubMenu" action:@selector(testSubMenu:)];
        mainMenuItems = [NSArray arrayWithObjects:testSubMenu, nil];

        UIMenuItem *subItem1 = [[UIMenuItem alloc] initWithTitle:@"Item1" action:@selector(item1:)];
        UIMenuItem *subItem2 = [[UIMenuItem alloc] initWithTitle:@"Item2" action:@selector(item2:)];
        subMenuItems = [NSArray arrayWithObjects:subItem1, subItem2, nil];

        [mc setMenuItems:mainMenuItems];

        [NSNotificationCenter defaultCenter] addObserver:self selector:@selector(onMenuItemDismissed:) name:UIMenuControllerDidHideMenuNotification object:nil];

        clickedShowSubMenu = NO;
    }
    return self;
}

- (void)testSubMenu:(id)sender{
    UIMenuController *mc = [UIMenuController sharedMenuController];
    [mc setMenuItems:subMenuItems];
    mc.menuVisible = YES; //from te doc, it say it would keep the menu not dismiss when this function end
    clickedShowSubMenu = YES;
}

- (void)item1:(id)sender{
}

- (void)item2:(id)sender{
}

- (void)onMenuItemDismissed:(id)sender{
    if(clickedShowSubMenu == YES){
        UIMenuController *mc = [UIMenuController sharedMenuController];
        [mc setMenuItems:mainMenuItems];
        clickedShowSubMenu = NO;
    }
}

- (BOOL)canPerformAction:(SEL)action withSender:(id)sender{
    if(action == @selector(testSubMenu:))return YES;
    else if(action == @selector(item1:))return YES;
    else if(action == @selector(item2:))return YES;
    return NO;
}

@end

It works when I select long touch some text and click the Test Sub Menu, it did appear the "subMenu": Item1 and Item2 on the same position that Test Sub Menu appear.

However, the problem is the second time and later. I select other text and the Test Sub Menu appear correctly, but when I click it ,the Item1 and Item2 is showed on the OLD position that it first appear. Their position is never changed. I do not know what cause this.

EDIT Ok. By making use of How to get coordinates (CGRect) for the selected text in UIWebView? to get the rect boundary of the selection and say [mc setTargetRect:theRect inView:self]; before mc.menuVisible = YES;

It work and the sub menu show approximate same position of the main menu. Is it recommended? There is still little problem that when I highlight a whole paragraph, the main menu is show UNDER the paragraph, however, the sub menu show ABOVE the paragraph.