You can create custom binding types to extend the runtime binding system. To create a custom binding type, create a class and inherit it from the CustomBinding class.
The CustomBinding is like the IBinding interface, which allows you to register multiple binding instances instead of a single one. The CustomBinding is an extensibility entry point and only provides an Update method to update the binding. However, you can implement the following methods to receive a callback when a binding is registered, unregistered, and when the data source context has changed on an element:
To define the data source and data source path for a binding type, implement the IDataSourceProvider interface. The binding system uses the dataSource and dataSourcePath properties provided by this interface to determine the resolved data source and data source path. These properties are referred to as “local” because they override the values obtained from the hierarchy. Importantly, modifying these “local” properties doesn’t impact the element itself or any of its descendants.
By default, the binding system updates a CustomBinding instance on every frame.
To define update triggers, use the following methods:
MarkDirty: Sets the binding object as dirty so that it gets updated during the next cycle.updateTrigger: Use this enum property to change how the binding is updated.BindingResult: Use this method to customize the update process. The BindingResult is a struct that tells you whether the update was successful. It contains a status and a message.The BindingResult contains a status and a message. The following are the possible values of status:
You can use the Pending result of the BindingResult method to inform the binding system if a binding object needs to be updated on the next cycle.
This section provides an example to demonstrate how to create a custom binding type and set up the binding in UI Builder, UXML, and C#.
The following example creates a custom binding type that displays the current time. You can bind it to the text property of a Label to create a clock.
[!code-cs[(Modules/UIElements/Tests/UIElementsExamples/Assets/Examples/CustomBinding_CurrentTime.cs)]
When you create a custom binding type, it appears in the Add binding window in UI Builder. To set up the binding in UI Builder, in the Add Binding window, select CurrentTimeBinding from the Type list.
The UXML equivalent of this binding is as follows:
<ui:Label text="Label">
<Bindings>
<CurrentTimeBinding property="text" />
</Bindings>
</ui:Label>
The C# equivalent of this binding is as follows:
var label = new Label();
label.SetBinding("text", new CurrentTimeBinding());
Follow these tips and best practices to optimize performance:
BindingUpdateTrigger.OnSourceChanged: When your binding type only requires updates when changes are detected in the source, set the updateTrigger to BindingUpdateTrigger.OnSourceChanged. This ensures that the binding type is updated only when necessary, optimizing performance.BindingUpdateTrigger.WhenDirty for manual updates: If you update your binding type manually and don’t require immediate synchronization, set the updateTrigger to BindingUpdateTrigger.WhenDirty. This allows you to manually control when the binding type updates, providing flexibility and control over synchronization.OnActivated, OnDeactivated, or OnDataSourceChanged callbacks instead of the Update callback. These callbacks are triggered at specific lifecycle events, reducing unnecessary updates and improving efficiency. By using the appropriate callback, you can optimize your binding type’s behavior and ensure updates occur precisely when needed.