CustomInventoriesAPI 1.19

This is basically an API, not a libraby, you have to install it as a plugin in plugins folder, after add it as dependecy on your project and start coding, this plugin doesn't use any type of database so it's really fast, also it have a item builder to make the things easier...

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Source (Updated)

Item builder :

Code (Java):

//Create the customItem
CustomItem customItem = CustomItem.builder(Material.REDSTONE).setName("&cRedstone").build();
//Conver the CustomItem to ItemStack
ItemStack itemStack = customItem.build();
//Since the API have variables you can also build the item like this to replace variables
ItemStack itemStack = customItem.build(Player);
 

Icons :

Code (Java):

//There are two types of Icons NormalIcon and Icon.

//First NormalIcon, to create a NormalIcon we will need a CustomItem
NormalIcon normalIcon = new NormalIcon(customItem);
//We can also put on the constructor the click type
NormalIcon normalIcon = new NormalIcon(customitem ,ClickType.LEFT_CLICK);
//Add actions, the actions is what will happen when somebody click on the Icon, to add an action :
normalIcon.addClickAction(new ClickAction() {
@Override
public void excute(Player player) {
  //Stuff
}
};

//We can also set permission
IPermission permission = new IPermission(plugin, "permission");
//If we wanna make our permission a child from a existing permission
IPermission permission = new IPermission(plugin, "permission", parent);

normalIcon.setPermission(permission);

//We can also set the visibility of the icon, ¿ what does this mean ? When a player opens the inventory and don't have the permission for the icon he won't be able to see the icon

normalIcon.setVisibilityRestricted(true);

//Icon, they main differente between NormalIcon and Icon is that when we intialize the Icon class we will have to implement an abstract method, also the constructor doesn't need a customItem.

Icon icon = new Icon() {
@Override
public CustomItem getCustomItem(Player player) {
  return customItem;
}
};

// When a player opens the inventory this will load the item, lets say we want to create an Icon with the player chestplate so we can easily do it like this, the icon will change depending on who opens the inventory.

Icon icon = new Icon() {
@Override
public CustomItem getCustomItem(Player player) {
  return CustomItem.toCustomItem(player.getInventory.getChestplate());
}
};
 

Create an inventory :

Code (Java):

//Create and Inventory and set an Icon
CustomInventory inventory = new CustomInventory(Size.ONE_LINE, title);

//Set an icon
inventory.setIcon(position, normalIcon);