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Add CascadingTypeParameter for automatic ItemType inference in GridView/DataGrid columns (#320)
* Initial plan * Add CascadingTypeParameter to GridView and DataGrid for automatic ItemType inference Co-authored-by: csharpfritz <78577+csharpfritz@users.noreply.github.com> * Update sample pages to demonstrate optional ItemType on columns Co-authored-by: csharpfritz <78577+csharpfritz@users.noreply.github.com> * Update documentation to explain ItemType cascading feature Co-authored-by: csharpfritz <78577+csharpfritz@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: csharpfritz <78577+csharpfritz@users.noreply.github.com>
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‎docs/DataControls/DataGrid.md‎

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@@ -15,6 +15,7 @@ The DataGrid component is meant to emulate the asp:DataGrid control in markup an
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- The `ItemCommand.CommandSource` object will be populated with the `ButtonField` object
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- DataGrid uses the same column types as GridView (BoundField, ButtonField, etc.)
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- DataGrid is a legacy control superseded by GridView in ASP.NET 2.0, but is provided for compatibility
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- **ItemType cascading** - The `ItemType` parameter is automatically cascaded from the DataGrid to child columns. You only need to specify it once on the DataGrid, and all child columns (BoundField, TemplateField, HyperLinkField, ButtonField) will automatically infer the type. For backward compatibility, you can still explicitly specify `ItemType` on individual columns if desired.
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## Web Forms Features NOT Supported
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‎docs/DataControls/GridView.md‎

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- The `RowCommand.CommandSource` object will be populated with the `ButtonField` object
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- **Context attribute** - When using `<TemplateField>`, add `Context="Item"` to access the current row item as `@Item` instead of Blazor's default `@context`
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- **ItemType cascading** - The `ItemType` parameter is automatically cascaded from the GridView to child columns. You only need to specify it once on the GridView, and all child columns (BoundField, TemplateField, HyperLinkField, ButtonField) will automatically infer the type. For backward compatibility, you can still explicitly specify `ItemType` on individual columns if desired.
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## Web Forms Declarative Syntax
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Visible=bool
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>
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<Columns>
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<!-- Note: ItemType is optional on columns and will be automatically
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inferred from the parent GridView. You can still explicitly
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specify ItemType on individual columns for clarity if desired. -->
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<BoundField
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DataField=string
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DataFormatString=string
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HeaderText=string
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ItemType=Type (optional, inferred from parent)
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Visible=bool
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>
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</BoundField>
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DataTextField="string"
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DataTextFormatString="string"
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HeaderText="string"
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ItemType=Type (optional, inferred from parent)
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NavigateUrl="uri"
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Target="string|_blank|_parent|_search|_self|_top"
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Text="string"
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Visible="True|False">
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</HyperLinkField>
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<TemplateField
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HeaderText=string
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ItemType=Type (optional, inferred from parent)
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Visible=bool
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>
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<ItemTemplate Context="Item">

‎samples/AfterBlazorServerSide/Components/Pages/ControlSamples/DataGrid/Default.razor‎

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SelectMethod="Customer.GetCustomers"
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EmptyDataText="No data available">
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<Columns>
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<BoundField ItemType="Customer" DataField="CustomerID" HeaderText="ID" />
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<BoundField ItemType="Customer" DataField="CompanyName" HeaderText="CompanyName" />
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<BoundField ItemType="Customer" DataField="FirstName" HeaderText="FirstName"/>
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<BoundField ItemType="Customer" DataField="LastName" HeaderText="LastName"/>
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<TemplateField ItemType="Customer">
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<BoundField DataField="CustomerID" HeaderText="ID" />
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<BoundField DataField="CompanyName" HeaderText="CompanyName" />
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<BoundField DataField="FirstName" HeaderText="FirstName"/>
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<BoundField DataField="LastName" HeaderText="LastName"/>
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<TemplateField>
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<ItemTemplate Context="Item">
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<button type="button">Click Me! @Item.FirstName</button>
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</ItemTemplate>
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</TemplateField>
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<ButtonField ItemType="Customer" ButtonType="ButtonType.Button" DataTextField="CompanyName" DataTextFormatString="{0}" CommandName="Customer"></ButtonField>
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<ButtonField ButtonType="ButtonType.Button" DataTextField="CompanyName" DataTextFormatString="{0}" CommandName="Customer"></ButtonField>
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</Columns>
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</DataGrid>
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<code>
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&lt;DataGrid ItemType="Customer" AutoGenerateColumns="false" DataKeyField="CustomerID"&gt;<br />
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&nbsp;&nbsp;&lt;Columns&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField ItemType="Customer" DataField="CustomerID" HeaderText="ID" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField ItemType="Customer" DataField="CompanyName" HeaderText="CompanyName" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;TemplateField ItemType="Customer"&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;!-- Note: ItemType is now optional on columns and inferred from parent DataGrid --&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField DataField="CustomerID" HeaderText="ID" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField DataField="CompanyName" HeaderText="CompanyName" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;TemplateField&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;ItemTemplate Context="Item"&gt;...&lt;/ItemTemplate&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;/TemplateField&gt;<br />
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&nbsp;&nbsp;&lt;/Columns&gt;<br />

‎samples/AfterBlazorServerSide/Components/Pages/ControlSamples/GridView/Default.razor‎

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SelectMethod="Customer.GetCustomers"
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EmptyDataText="No data available">
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<Columns>
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<BoundField ItemType="Customer" DataField="CustomerID" HeaderText="ID" />
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<BoundField ItemType="Customer" DataField="CompanyName" HeaderText="CompanyName" />
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<BoundField ItemType="Customer" DataField="FirstName" HeaderText="FirstName"/>
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<BoundField ItemType="Customer" DataField="LastName" HeaderText="LastName"/>
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<TemplateField ItemType="Customer">
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<BoundField DataField="CustomerID" HeaderText="ID" />
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<BoundField DataField="CompanyName" HeaderText="CompanyName" />
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<BoundField DataField="FirstName" HeaderText="FirstName"/>
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<BoundField DataField="LastName" HeaderText="LastName"/>
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<TemplateField>
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<ItemTemplate Context="Item">
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<button type="button">Click Me! @Item.FirstName</button>
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</ItemTemplate>
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</TemplateField>
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<ButtonField ItemType="Customer" ButtonType="ButtonType.Button" DataTextField="CompanyName" DataTextFormatString="{0}" CommandName="Customer"></ButtonField>
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<ButtonField ButtonType="ButtonType.Button" DataTextField="CompanyName" DataTextFormatString="{0}" CommandName="Customer"></ButtonField>
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</Columns>
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</GridView>
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<code>
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&lt;GridView ItemType="Customer" AutoGenerateColumns="false" DataKeyNames="CustomerID"&gt;<br />
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&nbsp;&nbsp;&lt;Columns&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField ItemType="Customer" DataField="CustomerID" HeaderText="ID" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField ItemType="Customer" DataField="CompanyName" HeaderText="CompanyName" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;TemplateField ItemType="Customer"&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;!-- Note: ItemType is now optional on columns and inferred from parent GridView --&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField DataField="CustomerID" HeaderText="ID" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;BoundField DataField="CompanyName" HeaderText="CompanyName" /&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;TemplateField&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&lt;ItemTemplate Context="Item"&gt;...&lt;/ItemTemplate&gt;<br />
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&nbsp;&nbsp;&nbsp;&nbsp;&lt;/TemplateField&gt;<br />
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&nbsp;&nbsp;&lt;/Columns&gt;<br />

‎samples/AfterBlazorServerSide/Components/Pages/ControlSamples/GridView/TemplateFields.razor‎

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AutoGenerateColumns="false"
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ItemType="SharedSampleObjects.Models.Widget">
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<Columns>
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<TemplateField HeaderText="Name" ItemType="SharedSampleObjects.Models.Widget">
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<TemplateField HeaderText="Name">
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<ItemTemplate Context="Item">
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<Label ID="lblName" Text="@Item.Name"></Label>
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</ItemTemplate>
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</TemplateField>
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<TemplateField HeaderText="Price" ItemType="SharedSampleObjects.Models.Widget">
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<TemplateField HeaderText="Price">
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<ItemTemplate Context="Item">
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<Label ID="lblPrice" Text="@Item.Price.ToString()"></Label>
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</ItemTemplate>

‎src/BlazorWebFormsComponents.Test/DataGrid/CascadedItemType.razor‎

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@code {
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[Fact]
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public void DataGrid_CascadedItemType_ColumnsInferTypeFromParent()
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{
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// Test that columns can omit ItemType when parent DataGrid has it
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// This uses the CascadingTypeParameter feature
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var cut = Render(@<DataGrid ItemType="Widget"
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AutoGenerateColumns="false"
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SelectMethod="GetWidgets">
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<Columns>
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<BoundField DataField="Id" HeaderText="ID" />
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<BoundField DataField="Name" HeaderText="Widget Name" />
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</Columns>
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</DataGrid>);
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// Check headers
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var tableHeaders = cut.FindAll("th");
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tableHeaders.Count.ShouldBe(2, "Wrong number of TH elements");
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tableHeaders[0].TextContent.ShouldBe("ID");
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tableHeaders[1].TextContent.ShouldBe("Widget Name");
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// Check first data row to see that it bound stuff correctly
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var firstDataRow = cut.FindAll("tr")[1]; // Row #0 is the header, so row #1 is the first data row
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var firstDataRowCells = firstDataRow.ChildNodes.OfType<AngleSharp.Dom.IElement>().ToList();
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var idCellHtml = firstDataRowCells[0].InnerHtml.Trim();
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idCellHtml.ShouldBe("1");
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var nameCellHtml = firstDataRowCells[1].InnerHtml.Trim();
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nameCellHtml.ShouldBe("First Widget");
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}
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[Fact]
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public void DataGrid_CascadedItemType_BackwardCompatibility()
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{
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// Test backward compatibility - explicit ItemType on columns should still work
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var cut = Render(@<DataGrid ItemType="Widget"
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AutoGenerateColumns="false"
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SelectMethod="GetWidgets">
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<Columns>
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<BoundField ItemType="Widget" DataField="Id" HeaderText="ID" />
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<BoundField ItemType="Widget" DataField="Name" HeaderText="Widget Name" />
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</Columns>
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</DataGrid>);
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var tableHeaders = cut.FindAll("th");
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tableHeaders.Count.ShouldBe(2);
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tableHeaders[0].TextContent.ShouldBe("ID");
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tableHeaders[1].TextContent.ShouldBe("Widget Name");
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}
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IQueryable<Widget> GetWidgets(int maxRows, int startRowIndex, string sortByExpression, out int totalRowCount)
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{
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totalRowCount = Widget.SimpleWidgetList.Length;
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return Widget.SimpleWidgetList.AsQueryable();
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}
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}

‎src/BlazorWebFormsComponents.Test/GridView/CascadedItemType.razor‎

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@code {
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[Fact]
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public void GridView_CascadedItemType_ColumnsInferTypeFromParent()
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{
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// Test that columns can omit ItemType when parent GridView has it
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// This uses the CascadingTypeParameter feature
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var cut = Render(@<GridView ItemType="Widget"
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AutoGenerateColumns="false"
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SelectMethod="GetWidgets">
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<Columns>
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<BoundField DataField="Id" HeaderText="ID" />
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<BoundField DataField="Name" HeaderText="Widget Name" />
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<BoundField DataField="LastUpdate.Year" HeaderText="Last Update Year" />
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</Columns>
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</GridView>);
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// Check headers
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var tableHeaders = cut.FindAll("th");
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tableHeaders.Count.ShouldBe(3, "Wrong number of TH elements");
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tableHeaders[0].TextContent.ShouldBe("ID");
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tableHeaders[1].TextContent.ShouldBe("Widget Name");
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tableHeaders[2].TextContent.ShouldBe("Last Update Year");
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// Check first data row to see that it bound stuff correctly
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var firstDataRow = cut.FindAll("tr")[1]; // Row #0 is the header, so row #1 is the first data row
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var firstDataRowCells = firstDataRow.ChildNodes.OfType<AngleSharp.Dom.IElement>().ToList();
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var idCellHtml = firstDataRowCells[0].InnerHtml.Trim();
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idCellHtml.ShouldBe("1");
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var nameCellHtml = firstDataRowCells[1].InnerHtml.Trim();
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nameCellHtml.ShouldBe("First Widget");
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var updateYearCellHtml = firstDataRowCells[2].InnerHtml.Trim();
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updateYearCellHtml.ShouldBe(Widget.SimpleWidgetList.First().LastUpdate.Year.ToString());
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}
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[Fact]
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public void GridView_CascadedItemType_MixedWithExplicitTypeStillWorks()
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{
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// Test backward compatibility - explicit ItemType on columns should still work
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var cut = Render(@<GridView ItemType="Widget"
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AutoGenerateColumns="false"
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SelectMethod="GetWidgets">
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<Columns>
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<BoundField ItemType="Widget" DataField="Id" HeaderText="ID" />
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<BoundField DataField="Name" HeaderText="Widget Name" />
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</Columns>
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</GridView>);
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var tableHeaders = cut.FindAll("th");
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tableHeaders.Count.ShouldBe(2);
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tableHeaders[0].TextContent.ShouldBe("ID");
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tableHeaders[1].TextContent.ShouldBe("Widget Name");
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}
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[Fact]
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public void GridView_CascadedItemType_TemplateFieldWorks()
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{
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// Test that TemplateField also benefits from cascaded type
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var cut = Render(@<GridView ItemType="Widget"
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AutoGenerateColumns="false"
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SelectMethod="GetWidgets">
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<Columns>
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<BoundField DataField="Id" HeaderText="ID" />
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<TemplateField HeaderText="Custom">
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<ItemTemplate Context="Item">
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<span>@Item.Name</span>
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</ItemTemplate>
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</TemplateField>
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</Columns>
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</GridView>);
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var tableHeaders = cut.FindAll("th");
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tableHeaders.Count.ShouldBe(2);
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tableHeaders[1].TextContent.ShouldBe("Custom");
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// Check that template rendered correctly
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var firstDataRow = cut.FindAll("tr")[1];
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var cells = firstDataRow.ChildNodes.OfType<AngleSharp.Dom.IElement>().ToList();
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cells[1].InnerHtml.Trim().ShouldContain("First Widget");
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}
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IQueryable<Widget> GetWidgets(int maxRows, int startRowIndex, string sortByExpression, out int totalRowCount)
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{
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totalRowCount = Widget.SimpleWidgetList.Length;
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return Widget.SimpleWidgetList.AsQueryable();
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}
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}

‎src/BlazorWebFormsComponents/DataGrid.razor‎

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@using BlazorWebFormsComponents.DataBinding
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@using Interfaces
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@typeparam ItemType
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@attribute [CascadingTypeParameter(nameof(ItemType))]
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@inherits DataBoundComponent<ItemType>
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@if (ColumnList.Any())
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{

‎src/BlazorWebFormsComponents/GridView.razor‎

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@using BlazorWebFormsComponents.DataBinding
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@using Interfaces
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@typeparam ItemType
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@attribute [CascadingTypeParameter(nameof(ItemType))]
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@inherits DataBoundComponent<ItemType>
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@if (ColumnList.Any())
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{

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