In a Blazor component, you can create a generic parameter for use in a method just as you can in a typical C# class. To do this, the syntax is:
@typeparam T
But I would like to know how to constrain it as you can in a C# class. Something like
// pseudocode
@typeparam T : ICloneable
For instance, I had the need to create the following component that allows a developer to pass a "Model" of generic type:
.../GESD.Blazor/Shared/GesdTrForm.razor
@typeparam modelType
<EditForm Model="@Model"
OnValidSubmit="@OnValidSubmit"
style="display:table-row"
>
@ChildContent
</EditForm>
@code {
[Parameter]
public RenderFragment ChildContent { get; set; }
[Parameter]
public modelType Model { get; set; } // here is the use of the generic
[Parameter]
public EventCallback<EditContext> OnValidSubmit { get; set; }
void demo () {
var cloned = Model.Clone();
}
}
But at .Clone()
I get the following error:
'modelType' does not contain a definition for 'Clone' ...
'.../GESD.Blazor/Shared/GesdTrForm.razor' creates a partial class called 'GesdTrForm' under the namespace 'GESD.Blazor.Shared'. Because it's a partial class, you can create a .cs file, delare the class as partial, and put the constraint in there.
.../GESD.Blazor/Shared/GesdTrForm.cs
using System;
namespace GESD.Blazor.Shared {
public partial class GesdTrForm<modelType> where modelType : ICloneable {}
}
For future searchers, I have just found that this feature is available in .NET 6.
Usage looks like:
@typeparam T where T : IMyInterface
If the generic type cannot be determined by the compiler then it can be specified explicitly:
<MyComponent T=MyType>
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