I wanna code a new event.

When the player open his inventory the event will be triggered.

But I don't know how to code it.

please help me!!!

For what you want to do, I don't think you need a custom event.  The inventory is a GUI and there is already events for GUIs being open.  I would create a handler for GuiOpenEvent and check if event.gui is an instance of an inventory gui.

 

But if you really wanted to create a custom event, here is some further info.

 

To create a custom event, I think that part is probably easy -- you extend an existing event like PlayerEvent and add the fields you additionally want to pass (if needed), you "post" the event to the event bus, and you register a handler for it.

 

To post an event to the bus, you can follow how the regular events are posted.  For example, here is the code for a built-in event posting:

        BlockEvent.HarvestDropsEvent event = new BlockEvent.HarvestDropsEvent(x, y, z, world, block, meta, fortune, dropChance, drops, player, silkTouch);
        MinecraftForge.EVENT_BUS.post(event);

 

However, the trick is you have to put the code that posts the event in the place you want it.  This is easy for your own code, but might be difficult in other cases.