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How can I restrict TModel to be classes only or to be implementing a specific interface?
@typeparam TModel
cannot get the syntax working.
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You can constrain the generic type by interface, thereby allowing only classes that implement that interface or classes that inherit from classes that implement the interface as the type parameter.
A type constraint on a generic type parameter indicates a requirement that a type must fulfill in order to be accepted as a type argument for that type parameter. (For example, it might have to be a given class type or a subtype of that class type, or it might have to implement a given interface.)
To create generic Blazor components, you can use the @typeparam directive. In the example below, I first use a component that doesn't have a code-behind file. Then I show what you need to do when you have a code-behind file. The main “trick” is to use a partial class.
C# allows you to use constraints to restrict client code to specify certain types while instantiating generic types. It will give a compile-time error if you try to instantiate a generic type using a type that is not allowed by the specified constraints.
From ASP.NET Core 6.0 onwards, you can use the following syntax to specify generic type constraints:
@typeparam TModel where TModel : IModel
The solution is to put the type constraint additionally in a partial code behind class. It works!
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