XAF Blazor - How to Implement a TreeList Editor to Display Hierarchical Data

Note
We created this example only for demonstration purposes. We can't guarantee that it will work in all usage scenarios. If you need to add some functionality to it, feel free to do this on your own. Researching DevExpress source code will help you with this task. Also, refer to the following help topic for more information: Debug DevExpress .NET Source Code with Debug Symbols. Unfortunately extending this example with custom code is outside the scope of our Support Service: Technical Support Scope.

Implement the following components to add the TreeList Editor to your ASP.NET Core Blazor application:

• A Razor component based on the DevExtreme TreeList widget.
• A component model that changes the state of the component.
• A component renderer that binds the component model with the component.
• A List Editor that integrates the component into your XAF application.

The following image demonstrates the result:

Alternative Solutions

Group List View Data Using DxGridListEditor

If this DevExtreme-based solution does not meet your requirements (for instance, you do not want to implement the ITreeNode contract in your data model from scratch or do not want to inherit your class from our HCategory), you can consider using the data grid and group by the 'Parent' property to emulate a tree: Group List View Data. In this case, it is also natural to enable a 'Split View' (MasterDetailMode = ListAndDetailView): Enable Split Layout in a List View.

Implement a Custom List Editor or View Item from Scratch

Of course, you can also build your own List Editor or View Item to display your custom data model using suitable DevExtreme or Blazor components: Using a Custom Control that is not Integrated by Default.

Implementation Details

ITreeNode-based Data Model

XAF has a built-in ITreeNode interface, which can be implemented by business objects to visualize them as a tree in a ListView (refer to the Category and related classes in this example). You can find more example code of ITreeNode-based data models below OR you can inherit your business class from our built-in HCategory class):

• EF Core: "c:\Program Files\DevExpress 2X.Y\Components\Sources\DevExpress.Persistent\DevExpress.Persistent.BaseImpl.EFCore\HCategory.cs"
• XPO: "c:\Program Files\DevExpress 2X.Y\Components\Sources\DevExpress.Persistent\DevExpress.Persistent.BaseImpl.Xpo\HCategory.cs"

This hierarchical data visualization is currently supported for WinForms and ASP.NET WebForms out-of-the-box (hence this example for ASP.NET Core Blazor).

Razor Component

1. Create a Razor class library (RCL) project (BlazorComponents). Reference it in your TreeListDemoEF.Blazor.Server project.

2. Register DevExtreme libraries in the TreeListDemoEF.Blazor.Server/Pages/_Host.cshtml page as described in the following topic: Add DevExtreme to a jQuery Application.

3. Add the TreeList.razor Razor component to the BlazorComponents project.

   The following table describes the APIs implemented in this component:

   API	Type	Description
   GetDataAsync	parameter	Encapsulates a method that fetches data on demand.
   FieldNames	parameter	Stores an array of field names.
   GetFieldDisplayText	parameter	Encapsulates a method that returns field captions.
   GetKey	parameter	Encapsulates a method that returns the current key value.
   HasChildren	parameter	Encapsulates a method that determines whether the currently processed node has child nodes.
   RowClick	parameter	Encapsulates a method that handles an event when users click a row.
   SelectionChanged	parameter	Encapsulates a method that handles an event when users change selection.
   OnRowClick and OnSelectionChanged	methods	Used to raise the RowClick and SelectionChanged events.
   OnAfterRenderAsync	method	Initializes the necessary IJSObjectReference, ElementReference, and DotNetObjectReference fields for interaction with the DevExtreme TreeList widget.
   OnGetDataAsync	method	Creates a dictionary of field name-value pairs. This method is called from JavaScript code to fetch data based on the passed parent key value.
   Refresh	method	Calls the JavaScript TreeList.refresh method.

4. Add the treeListModule.js script with the TreeList API to the BlazorComponents\wwwroot folder. In the script, configure TreeList to load data on demand as described in the following article: Load Data on Demand. Use the DotNetObjectReference object to call the declared .NET OnGetDataAsync method and fetch data. Handle the TreeList.rowClick and TreeList.selectionChanged events to call the declared .NET OnRowClick and OnSelectionChanged methods.

See also:

• Call .NET methods from JavaScript functions in ASP.NET Core Blazor
• Call JavaScript functions from .NET methods in ASP.NET Core Blazor
• Tree List > Data Binding > Load Data on Demand

Component Model

1. In the Blazor project (TreeListDemoEF.Blazor.Server), create the ComponentModelBase descendant and name it TreeListModel.cs.

   The following table describes the APIs implemented in this component:

   API	Type	Description
   GetDataAsync	property	Encapsulates a method that fetches data on demand.
   FieldNames	property	Stores an array of field names.
   GetFieldDisplayText	property	Encapsulates a method that returns field captions.
   GetKey	property	Encapsulates a method that returns the current key value.
   HasChildren	property	Encapsulates a method that determines whether the currently processed node has child nodes.
   RowClick, SelectionChanged, RefreshRequested	events	Occur when users click a row and change selection.
   OnRowClick, OnSelectionChanged, Refresh	methods	Used to raise the corresponding events.

2. Create EventArgs descendants to pass key values to the RowClick and SelectionChanged event handlers. See these classes in the following file: TreeListModel.cs.

Component Renderer

1. In the Blazor project (TreeListDemoEF.Blazor.Server), create a new Razor component and name it TreeListRenderer.razor. This component renders the TreeList component from the RCL project.
2. Ensure that the component’s Build Action property is set to Content.
3. Declare the required parameters and implement the IDisposable interface.

List Editor

1. Create a ListEditor descendant, apply the ListEditorAttribute to this class, and pass an ITreeNode type as a parameter.
2. Implement the IComplexListEditor interface. In the IComplexListEditor.Setup method, initialize an Object Space instance.

The following table describes the API implemented in this List Editor:

API	Type	Description
SelectionType	property	Returns SelectionType.Full. This setting allows users to open the Detail View by click.
CreateControlsCore	method	Returns an instance of the TreeList component.
AssignDataSourceToControl	method	Assigns the List Editor’s data source to the component model. If the data source implements the IBindingList interface, this method handles data change notifications.
OnControlsCreated	method	Passes methods to the created delegates, initializes the arrays of field names, and subscribes to the component model’s RowClick and SelectionChanged events.
BreakLinksToControls	method	Unsubscribes from the component model’s events and resets its data to release resources.
Refresh	method	Calls the component model's Refresh method to update the List Editor layout when its data is changed.
GetSelectedObjects	method	Returns an array of selected objects.

Supported Data Access mode

As the created tree list editor supports only the 'Client' Data Access mode, you need to use the RegisterEditorSupportedModes method as shown here:

xaf-treelist-editor-blazor/CS/EFCore/TreeListDemoEF/TreeListDemoEF.Blazor.Server/BlazorModule.cs

Line 21 in 34ef525

DataAccessModeHelper.RegisterEditorSupportedModes(typeof(TreeListEditor), new[] { CollectionSourceDataAccessMode.Client });

Files to Review

• BlazorComponents/TreeList.razor
• BlazorComponents/wwwroot/treeListModule.js
• EFCore/XAFTreeList.Module.Blazor/Editors/TreeListModel.cs
• EFCore/XAFTreeList.Module.Blazor/Editors/TreeListRenderer.razor
• EFCore/XAFTreeList.Module.Blazor/Editors/TreeListEditor.cs

Documentation

• How to: Use a Custom Component to Implement List Editor (Blazor)
• Using a Custom Control that is not Integrated by Default

More Examples

• Use a Custom Component to Implement List Editor (Blazor)

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