Add CascadingTypeParameter for automatic ItemType inference in GridView/DataGrid columns

[Copilot]

GridView and DataGrid required redundant ItemType specification on every child column component (BoundField, TemplateField, HyperLinkField, ButtonField), creating verbose markup prone to type mismatches.

Changes

• Added @attribute [CascadingTypeParameter(nameof(ItemType))] to GridView.razor and DataGrid.razor
• Child columns now automatically infer ItemType from parent component
• Updated sample pages and documentation to demonstrate simplified syntax

Impact

Before:

<GridView ItemType="Customer" AutoGenerateColumns="false">
  <Columns>
    <BoundField ItemType="Customer" DataField="Name" HeaderText="Name" />
    <BoundField ItemType="Customer" DataField="Email" HeaderText="Email" />
    <TemplateField ItemType="Customer" HeaderText="Actions">
      <ItemTemplate Context="Item">...</ItemTemplate>
    </TemplateField>
  </Columns>
</GridView>

After:

<GridView ItemType="Customer" AutoGenerateColumns="false">
  <Columns>
    <BoundField DataField="Name" HeaderText="Name" />
    <BoundField DataField="Email" HeaderText="Email" />
    <TemplateField HeaderText="Actions">
      <ItemTemplate Context="Item">...</ItemTemplate>
    </TemplateField>
  </Columns>
</GridView>

Fully backward compatible—explicit ItemType on columns continues to work.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Pass through ItemTypes to childcomponents</issue_title>
<issue_description>Example: For a GridView, need to pass the ItemType of the Grid through to the column child components so that we don't have to repeat the ItemType on each of the child components</issue_description>

<agent_instructions>I think we can do this with a cascading parameter type or something like that</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@csharpfritz Very interesting approach... I like the simplicity of the approach and re-use of other components we've already completed

Jeff

On Fri, Apr 17, 2020 at 3:45 AM Egil Hansen notifications@github.com
wrote:

I like the general idea of implementing the GridView through the ListView.
Users should not see a difference on the surface.

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• Fixes Pass through ItemTypes to childcomponents #163

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