Well, the part he’s showing is how to create the inventory slot, which goes inside the inventory, and that’s done by deleting the canvas.
Maybe you’re wondering, why not add buttons to the inventory and have them as slots? That would be a programming nightmare.
By making the inventory slot from a separate widget, you get a great deal of control of how it behaves and without this way of doing things you probably couldn’t do things like drag & drop operations.
So what’s with these deep hierarchies? And I agree, I find myself creating silly deep hierarchies when creating some widgets, but then again… there’s not much choice.
For example, the border can only have 1 child, so instead of directly filling the border with the stuff you want, you first have to add something that can hold more children.
Or, if you want two elements beside each other you have to use the horizontal box.
As for the size box, by default the widget components added tend to either try to take as little space as possible or as much as possible, if you want them to be a certain size, you got to use the size box. It’s a bit of a hassle.
I think I started by just reading the UE docs on umg while playing around with it in the engine. You will find yourself wanting to add something to something else, but you can’t since it can only have one child and it already has it, so you need to add something that can hold more children.
Want to create something with a header and a body which is divided into…? Okay start with the first part. Header and body are layout vertically, so you need a vertical box. Then look at the layout you want the body to be. It just kind of makes sense after a couple of days of messing around.