Razor component disconnects Blazor when passing a class instance

[mrlife]

When visiting Index.cshtml, the browser console displays the below errors.

Index.cshtml

@{
	var myObject = new MyClass(1, "test");
}

<component type="typeof(MyComponent)" render-mode="ServerPrerendered" param-MyObject="@myObject" />

MyClass.cs

public class MyClass
{
	public int MyInt { get; set; }
	public string MyString { get; set; }

	public MyClass(int myInt, string myString)
	{
		MyInt = myInt;
		MyString = myString;
	}
}

MyComponent.razor

<p>
	@MyObject.MyInt
	@MyObject.MyString
</p>

@code {
	[Parameter]
	public MyClass MyObject { get; set; }
}

Browser console

Error: The list of component records is not valid.
Information: Connection disconnected.
Unhandled Promise Rejection: Error: Invocation canceled due to the underlying connection being closed.

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

Further technical details

• ASP.NET Core version
• Include the output of dotnet --info
• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version

[guardrex]

Related doc issue 👉 dotnet/AspNetCore.Docs#17210

... but I don't repro any such error here.

[pranavkm]

@mrlife parameters passed to the component need to be serializable by System.Text.Json. System.Text.Json does not support immutable types - https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-migrate-from-newtonsoft-how-to#deserialize-to-immutable-classes-and-structs. You'll need to have a public parameterless constructor for this to work correctly.

@javiercn the exception should be thrown here: https://github.com/dotnet/aspnetcore/blob/master/src/Components/Server/src/Circuits/ComponentParameterDeserializer.cs#L68, but the exception is logged as Debug. Should this be surfaced more readily to the user?

[mrlife]

@pranavkm Thanks for letting me know. I just tried it out, and it seems to work. Is this right?

Code

var myObject = new MyClass(1, "test");
var serialized = System.Text.Json.JsonSerializer.Serialize(myObject);

Contents of serialized

"{"MyInt":1,"MyString":"test"}"

[pranavkm]

It's the deserialization routine that needs a parameterless constructor.

[mrlife]

It's the deserialization routine that needs a parameterless constructor.

This is true, thank you. It works when serializing but does throw a runtime error when deserializing.

NotSupportedException: Deserialization of reference types without parameterless constructor is not supported.

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