Your new editor window won't display itself, and so, at the start of this recipe, it is mentioned that you should have implemented a custom menu or toolbar button or a console command that we can use to trigger the display of our new window.
All of Slate's widgets are usually interacted with in the form of TSharedRef< > or TSharedPtr< >.
The SNew() function returns a TSharedRef that's been templated on the requested widget class.
As we mentioned previously, Slate widgets have a number of functions that they implement, which all return the object that the function was invoked on. This allows for method chaining to be used to configure the object at creation time.
This is what allows for the Slate syntax of <Widget>.Property(Value).Property(Value).
The properties that are set on the widget in this recipe are the window title, the window size, and whether the window can be maximized and minimized.
Once all the requisite properties on a widget have been set, the bracket operators ([]) can be used to specify the content to be placed inside the widget, for example, a picture or label inside a button.
SWindow is a top-level widget with only one slot for child widgets, so we don't need to add a slot for it ourselves. We place content into that slot by creating it inside the pair of brackets.
The content we create is SVerticalBox, which is a widget that can have an arbitrary number of slots for child widgets that are displayed in a vertical list.
For each widget we want to place into the vertical list, we need to create a slot.
The easiest way to do this is to use the overloaded + operator and the SVerticalBox::Slot() function.
Slot() returns a widget like any other, so we can set properties on it like we did on our SWindow.
This recipe centers the Slot's content on both horizontal and vertical axes using HAlign and VAlign.
A Slot has a single child widget, and it's created inside the [] operators, just like they are for SWindow.
Inside the Slot content, we create a text block with some custom text.
Our new SWindow now has its child widgets added, but it isn't being displayed yet because it hasn't been added to the window hierarchy.
The main frame module is used to check if we have a top-level editor window, and if it exists, our new window is added as a child.
If there's no top-level window to be added as a child to, then we use the Slate Application singleton to add our window without a parent.
If you would like to see the hierarchy of the window we've created, you can use the Slate Widget Reflector, which can be accessed via Window | Developer Tools | Widget Reflector.
If you select Pick Painted Widget and hover your cursor over the text in the center of our custom window, you will be able to see the SWindow with our custom widgets added to its hierarchy:
