Custom inventory checking a few things

When I make a custom inventory, I attempt to make an inventory menu.

How do I do the following:
- Check to see if the item clicked is NOT from the players inventory

 

Just do:

Code:

if(!event.getInventory().getTitle().equalsIgnoreCase("Your title")) {
//Player has clicked item which is not in your custom inventory. 
} 

or something along the lines of that.

 

I do that, I although if the player clicks a stone in his inventory, it some how acts as if he clicked it from the custom inventory.

 

@Neilnet What I do is add a lore to the inventory's items, if you really don't want a lore, you can add an empty lore like
lore.add(ChatColor.RED +"" + ChatColor.BLUE + ""); Then check if the item clicked has a lore (ChatColor.RED +"" + ChatColor.BLUE + "")

 

That'll work, cheers.