Inventory Viewmodels
To exchange backend data with the UI, the Inventory System uses UMG Viewmodels. They support event-driven bindings that can trigger changes in the User Interface, when an update happens in the backend.
There are two categories of Viewmodels in the project:
Inventory: These will provide information and broadcast changes about the Layout, Attributes and Item Lists.
Item: These will provide information and broadcast changes from Fragments. You can expect a one-to-one relationship between Fragments and Viewmodels.
Initializing Viewmodels
You can decide what is the best way to initialize your Viewmodels. For the Inventory itself, it might be easier to simply initialize all pertinent view models during along with the widget's initialization.
As for the Items, you might need to ponder if you can have each item initializing all view models right away or manually initialize them and destroy them in more appropriate situations.
Regardless, it's recommended to have your Viewmodels configured to initialize along with each Item's widget, while the Inventory UI is being built. Once completed, you can profile and evaluate what is the best initialization strategy.
Inventory Initialization
Viewmodels that will connect to the Inventory itself will usually do so when the Inventory Manager broadcasts its initialization event. At that moment, Inventory Widgets connected to Viewmodels will broadcast any appropriate data.
Container Initialization
Certain Viewmodels must connect to Containers. this can be done in two ways:
By invoking the
SetContainerfunction at any appropriate moment. This will allow the Viewmodel to bind to the Container's delegates.Owning widgets will have a container set in their properties, or will receive one. When that happens, they will invoke the
SetContainerfunction.
Item Initialization
Similar to the Container Initialization, Viewmodels connected to Items will do so in two ways:
By invoking the
SetItemfunction at any appropriate moment. This will allow the Viewmodel to bind to the Item's delegates.Owning widgets storing items will invoke the
SetItemfunction whenever items are created. They will also sendnullvalues for empty items.
Binding Viewmodels
Viewmodels will expose properties that can be bound to Properties and Functions. These elements will be notified about any changes in the viewmodel's data, allowing them to and update accordingly.
Binding to Variables
Binding viewmodels to variables is the simplest form of integration between the backend and the UI. Whenever a value changes in the backend data, the variable will be updated to reflect that change. Here are some examples:
Binding the Inventory Window Title to the Layout's Display Name.
Binding the Stack fragment data to an Item's widget, so the current stack size is displayed.
Binding the Weight fragment data to an Item's widget, so the base and total weight are displayed.
Binding to Function
Binding viewmodels to Functions is a powerful way to trigger more complicated behavior that usually involves many aspects of the user interface. Here are some examples:
Binding to changes in Container Items to update an entire container.
Binding to the Quality Color to change the title and background color of an item widget.
Set a widget's visibility based on a boolean value.
Applying Conversions
Binding to a Function certainly allows a lot of flexibility while converting values between a viewmodel and a widget. Many functions are already available in the form of Conversions, which you can leverage in many ways, such as:
Convert a numeric value to a text representation, including rounding and grouping settings.
Modify texts to trim, or change case.