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(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary 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.
using System;
using Unity.Properties;
using UnityEngine.UIElements;
[UxmlObject]
public partial class CurrentTimeBinding : CustomBinding
{
[UxmlAttribute]
public string timeFormat = "HH:mm:ss";
public CurrentTimeBinding()
{
updateTrigger = BindingUpdateTrigger.EveryUpdate;
}
protected override BindingResult Update(in BindingContext context)
{
var timeNow = DateTime.Now.ToString(timeFormat);
var element = context.targetElement;
if (ConverterGroups.TrySetValueGlobal(ref element, context.bindingId, timeNow, out var errorCode))
return new BindingResult(BindingStatus.Success);
// Error handling
var bindingTypename = TypeUtility.GetTypeDisplayName(typeof(CurrentTimeBinding));
var bindingId = $"{TypeUtility.GetTypeDisplayName(element.GetType())}.{context.bindingId}";
return errorCode switch
{
VisitReturnCode.InvalidPath => new BindingResult(BindingStatus.Failure, $"{bindingTypename}: Binding id `{bindingId}` is either invalid or contains a `null` value."),
VisitReturnCode.InvalidCast => new BindingResult(BindingStatus.Failure, $"{bindingTypename}: Invalid conversion from `string` for binding id `{bindingId}`"),
VisitReturnCode.AccessViolation => new BindingResult(BindingStatus.Failure, $"{bindingTypename}: Trying set value for binding id `{bindingId}`, but it is read-only."),
_ => throw new ArgumentOutOfRangeException()
};
}
}
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.