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Observable Data

Databound components can benefit from live data - when the data source collection changes, the components should update to reflect that change. Most data-bound components in the Telerik UI for Blazor suite implement such functionality.

When the Data of the component is a collection that implements the INotifyCollectionChanged interface (such as ObservableCollection), the Telerik components subscribe to its CollectionChanged event to update. This means that adding items, removing items, or clearing the collection updates the components (its .Add(), .Remove() and .Clear() methods).

The following components support observable data for their Data parameter:

  • AutoComplete

  • ComboBox

  • DropDownList

  • Grid

  • ListView

  • MultiSelect

  • TreeList

  • TreeView

The Scheduler, Menu, Drawer, ContextMenu will receive this feature in a future release.

Refresh Data

The most common reason you would use an ObservableCollection is to make a component (like a grid, treeview, treelist, dropdown) change or react when you change that collection.

When you want to refresh the component data source like that, there are two important framework behaviors you need to be aware of:

  • Observable collections fire the CollectionChanged event (which the Telerik components subscribe to) only when their Add, Remove and Clear methods are called.

    They do not fire it when you change the value of a field of one of their elements.

  • In Blazor, the framework will fire the OnParametersSet event of a child component (which is how child components can react to outside changes) only when it can detect a change in the object it receives through the corresponding parameter (like Data for the data sources of Telerik components). This detection works as follows:

    • For primitive types (such as numbers, strings), this happens when their value changes.

    • For complex types (such as data collections like List, or any IEnumerable, and application-specific models/objects), this happens when the object reference changes.

      Thus, you would usually need to create a new reference for the view-model field (such as TreeViewData = new List<MyTreeViewItem>(theUpdatedDataCollection);) when you want the component to update.

You can find some more explanations and examples for the Grid component in the Force a Grid to Refresh Knowledge Base article.

See Also

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