PanelBar - 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:
Rebind Method
You can refresh the data by invoking the Rebind method. Use the component reference to call the Rebind method after you have made the data changes (for example adding, removing items). This is needed in case you are not using Observable data or resetting the collection reference. Calling Rebind will force the component process the available data anew to reflect the updates.
Use the Rebind method to refresh the data.
@* Add/remove an item and rebind the PanelBar to react to that change. *@
<TelerikButton OnClick="@AddItem">Add item</TelerikButton>
<TelerikButton OnClick="@RemoveItem">Remove first item</TelerikButton>
<TelerikPanelBar @ref="@PanelBarRef"
Data="@Items">
</TelerikPanelBar>
@code {
private TelerikPanelBar PanelBarRef;
private List<PanelBarItem> Items { get; set; }
private void AddItem()
{
Items.Add(new PanelBarItem()
{
Text = "Item 4"
});
PanelBarRef.Rebind();
}
private void RemoveItem()
{
Items.RemoveAt(0);
PanelBarRef.Rebind();
}
protected override void OnInitialized()
{
Items = GenerateData();
base.OnInitialized();
}
private List<PanelBarItem> GenerateData()
{
List<PanelBarItem> collection = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1.1"
},
new PanelBarItem()
{
Text = "Item 1.2",
Disabled = true,
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1.2.1"
},
new PanelBarItem()
{
Text = "Item 1.2.2"
}
}
}
}
},
new PanelBarItem()
{
Text = "Item 2",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 2.1",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 2.1.1"
}
}
},
new PanelBarItem()
{
Text = "Item 2.2",
Url = "https://google.com"
}
}
},
new PanelBarItem()
{
Text = "Item 3"
}
};
return collection;
}
public class PanelBarItem
{
public string Text { get; set; }
public bool Disabled { get; set; }
public string Url { get; set; }
public List<PanelBarItem> Items { get; set; }
}
}
Observable Data
Databound components can benefit from live updates - 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 make live 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.
Bind the PanelBar to an ObservableCollection, so it can react to collection changes.
@* Add/remove an item to see how the PanelBar reacts to that change. *@
@using System.Collections.ObjectModel
<TelerikButton OnClick="@AddItem">Add item</TelerikButton>
<TelerikButton OnClick="@RemoveItem">Remove first item</TelerikButton>
<TelerikPanelBar Data="@Items"/>
@code {
private ObservableCollection<PanelBarItem> Items { get; set; }
private void AddItem()
{
Items.Add(new PanelBarItem()
{
Text = "Item 4"
});
}
private void RemoveItem()
{
Items.RemoveAt(0);
}
protected override void OnInitialized()
{
Items = GenerateData();
base.OnInitialized();
}
private ObservableCollection<PanelBarItem> GenerateData()
{
ObservableCollection<PanelBarItem> collection = new ObservableCollection<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1.1"
},
new PanelBarItem()
{
Text = "Item 1.2",
Disabled = true,
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1.2.1"
},
new PanelBarItem()
{
Text = "Item 1.2.2"
}
}
}
}
},
new PanelBarItem()
{
Text = "Item 2",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 2.1",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 2.1.1"
}
}
},
new PanelBarItem()
{
Text = "Item 2.2",
Url = "https://google.com"
}
}
},
new PanelBarItem()
{
Text = "Item 3"
}
};
return collection;
}
public class PanelBarItem
{
public string Text { get; set; }
public bool Disabled { get; set; }
public string Url { get; set; }
public List<PanelBarItem> Items { get; set; }
}
}
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 strings and value types, this happens when their value changes.
-
For reference types (such as data collections like
List, or anyIEnumerable, and application-specific objects), this happens when the object reference changes.Thus, you would usually need to create a
newreference for the view-model field (such asTreeViewData = new List<MyTreeViewItem>(theUpdatedDataCollection);) when you want the component to update.
Create new collection reference to refresh the PanelBar data.
@* Add/remove an item to see how the PanelBar reacts to that change. *@
<TelerikButton OnClick="@AddItem">Add item</TelerikButton>
<TelerikButton OnClick="@RemoveItem">Remove first item</TelerikButton>
<TelerikPanelBar Data="@Items"/>
@code {
private List<PanelBarItem> Items { get; set; }
private void AddItem()
{
Items.Add(new PanelBarItem()
{
Text = "Item 4"
});
Items = new List<PanelBarItem>(Items);
}
private void RemoveItem()
{
Items.RemoveAt(0);
Items = new List<PanelBarItem>(Items);
}
protected override void OnInitialized()
{
Items = GenerateData();
base.OnInitialized();
}
private List<PanelBarItem> GenerateData()
{
List<PanelBarItem> collection = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1.1"
},
new PanelBarItem()
{
Text = "Item 1.2",
Disabled = true,
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 1.2.1"
},
new PanelBarItem()
{
Text = "Item 1.2.2"
}
}
}
}
},
new PanelBarItem()
{
Text = "Item 2",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 2.1",
Items = new List<PanelBarItem>()
{
new PanelBarItem()
{
Text = "Item 2.1.1"
}
}
},
new PanelBarItem()
{
Text = "Item 2.2",
Url = "https://google.com"
}
}
},
new PanelBarItem()
{
Text = "Item 3"
}
};
return collection;
}
public class PanelBarItem
{
public string Text { get; set; }
public bool Disabled { get; set; }
public string Url { get; set; }
public List<PanelBarItem> Items { get; set; }
}
}