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Context Menu - 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 - when ObservableCollection instances fire events, and how to refresh the data of a component when it is not an observable collection.

In this article:

Observable Data

The Context Menu will receive this feature in a future release. You can currently refresh its Data by creating a New collection reference.

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 Observable collections fire the CollectionChanged event 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.

New Collection Reference

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.

Create new collection reference to refresh the Context Menu data.

@* Add/remove an item or change the data collection to see how the Context Menu reacts to that change. *@

<TelerikButton OnClick="@AddItem">Add item</TelerikButton>

<TelerikButton OnClick="@RemoveItem">Remove item</TelerikButton>

<TelerikButton OnClick="@ChangeData">Change data</TelerikButton>

<div id="context-menu-target" style="background:yellow; width:200px; height:50px">right click for context menu</div>

<TelerikContextMenu Data="@MenuData"
                    Selector="#context-menu-target"
                    IconField="@nameof(MenuModel.TelerikIcon)"
                    ImageUrlField="@nameof(MenuModel.MyImage)"
                    IconClassField="@nameof(MenuModel.MyIconClass)">
</TelerikContextMenu>

@code {
    public List<MenuModel> MenuData { get; set; }

    void AddItem()
    {
        MenuData.Add(
            new MenuModel()
            {
                Text = "Info",
                TelerikIcon = "info-circle"
            });
        MenuData = new List<MenuModel>(MenuData);
    }

    void RemoveItem()
    {
        if (MenuData.Count > 0)
        {
            MenuData.RemoveAt(MenuData.IndexOf(MenuData.Last()));
            MenuData = new List<MenuModel>(MenuData);
        }
    }

    void ChangeData()
    {
        MenuData = new List<MenuModel>()
        {
            new MenuModel()
            {
                Text = "Copy",
                TelerikIcon = "copy"
            },
            new MenuModel()
            {
                Text = "Cut",
                TelerikIcon = "cut"
            }
        };
        MenuData = new List<MenuModel>(MenuData);
    }

    protected override void OnInitialized()
    {
        MenuData = new List<MenuModel>()
        {
            new MenuModel()
            {
                Text = "IconField",
                TelerikIcon = "email"
            },
            new MenuModel()
            {
                Text = "IconClassField",
                MyIconClass = "oi oi-wrench",
            },
            new MenuModel()
             {
                Text = "ImageUrlField",
                MyImage = "https://docs.telerik.com/blazor-ui/images/video.png"
             }
        };
    }

    public class MenuModel
    {
        public string Text { get; set; }
        public string TelerikIcon { get; set; }
        public string MyImage { get; set; }
        public string MyIconClass { get; set; }
    }
}

See Also

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