[Blazor] Explicitly set values should trump splatted attributes

The position of @attributes relative to the position of element attributes is important. When @attributes are splatted on the element, the attributes are processed from right to left (last to first)

https://docs.microsoft.com/en-us/aspnet/core/blazor/components/?view=aspnetcore-3.1

Attributes having to have a special order is not immediately obvious when trying to understand why an explicitly set parameter value is incorrect.

The position of @attributes should be irrelevant. The @attributes should be splatted first so that explicitly set parameters cannot be overridden by the consumer of the component.

[mrpmorris]

Ah no, not that it matters now, but you were thinking of a different approach.

All you have to do is this

[Parameter]
public string Something { get; set; }

protected override async SetParametersAsync(ParameterView parameters)
{
  await base.SetParametersAsync(parameters);
  if (Something is null)
    Something = "the default value";
}

[javiercn]

I don’t understand what this means.

The way SetParametersAsync is implemented today, if you override you’ll have to call base for things like OnInitialized to run when extending componentbase (the most common case). If you override, do something and call base afterwards, it will have no effect since the base implementation will set the parameters. If you call base and then do something afterward, all the OnInititalized and OnParametersSet will run with the wrong set of parameter values. That is something we could fix by introducing an additional lifecycle method that can be overriden, but we haven’t seen the need for it yet.