Documentation

Unity Engine

User Manual

Script Reference

Unity Engine

Define binding mode and update trigger

Define binding modes and update triggers to configure how changes are replicated between the data source and the UI.
Read time 2 minutesLast updated a month ago
To define how changes are replicated between the data source and the UI, you can set the binding mode and update triggers for a binding object. You can set the binding mode and update triggers in UI Builder, UXML, or C#.

Define binding modes

Binding modes configure how changes are replicated between the data source and the UI. The following binding modes are available:
  • TwoWay: Changes are replicated from the data source to the UI and from the UI to the data source. This is the default binding mode.
  • ToTarget: Changes are replicated from the data source to the UI only.
  • ToSource: Changes are replicated from the UI to the data source only.
  • ToTargetOnce: Changes are replicated from the data source to the UI only once, unless it's marked as dirty.
Tip
Ensure that you set the appropriate binding mode based on your needs. For example, to prevent changes in the UI from being reflected in the source or if the UI is read-only, set the 
bindingMode
to 
BindingMode.ToTarget
.

Define update triggers

You can update binding objects on every frame or when a change occurs in the data source. The following update triggers are available:
  • Every frame
  • On change detection or every frame if change detection is impossible. Refer to Define data sources for more details.
  • When explicitly marked as 
    dirty
To define update triggers, use the following properties:
  • MarkDirty
    : Sets the binding object as 
    dirty
    , so that it gets updated during the next cycle.
  • updateTrigger
    : Updates a binding object on every frame, regardless of the data source version.
Note
Don't keep per-element states in your binding types as much as possible. You can use a binding instance across multiple elements and properties simultaneously. During updates and callbacks, the binding system passes in a context object that contains the target element, binding ID, and relevant data. You can't use the context object itself to store the per-element state, but you can use it to store data as a key in a dictionary.

Additional resources