Blazor WASM: Unhandled exception Object of type T has a property matching the name, but it does not have [ParameterAttribute] applied

Question

I'm a bit stumped here because I do have the parameter attribute applied. I seem to be simply following the documentation in a one to one fashion.

Error message

Unhandled exception rendering component: Object of type 'Onero.Client.Features.CourseManager.CourseModelRegister' has a property matching the name 'HighSchoolRegistrationModelId', but it does not have [ParameterAttribute] applied.

Component hierarchy

//parent

<CascadingValue Value="HighSchoolRegistrationModelId">
    <CourseModelAddForm></CourseModelAddForm>
</CascadingValue>

@code {
    public long HighSchoolRegistrationModelId;
    protected override async Task OnInitializedAsync()
    {
        await base.OnInitializedAsync();
        HighSchoolRegistrationModelId = await CourseService.GetHighSchool();
    }
}

//middle component
@if (add)
{
    <CourseModelRegister HighSchoolRegistrationModelId="@HighSchoolRegistrationModelId"> 
    </CourseModelRegister>
}

@code {
    [CascadingParameter] 
    protected long HighSchoolRegistrationModelId { get; set; }
    private bool add = false;
    protected override async Task OnParametersSetAsync()
    {
        await base.OnParametersSetAsync();
    }
    private void ShowAddForm()
    {
        add = true;
    }
}

//Grandchild where error occurs

@code {
    [CascadingParameter] 
    protected long HighSchoolRegistrationModelId { get; set; }
   // rest of code omitted
}

Am I missing something? Perhaps this has to do with lifecycle management? I tried using OnInitialized as well as OnParametersSet.

I know it has been 2 months, have you had a chance to find an answer to this? — Shuryno
– Shuryno, Commented Dec 14, 2021 at 14:36
No, I vaguely recall seeing somewhere that there was an error with passing to grandchildren that needed to be fixed. I ended up just using Parameter and it worked well enough. — amdorsey12
– amdorsey12, Commented Dec 17, 2021 at 0:42
Did you finally handle it? I have the same problem, and in my case seems the DynamicComponent component (which is in between) is breaking the cascade — Santiago
– Santiago, Commented Aug 31, 2022 at 14:31

Shuryno · Accepted Answer · 2021-12-17 14:06:01Z

3

I am pretty I have found the issue, I had the exact same situation, and its because I was passing value to the component's parameter and it was define as a [CascadingParameter], so it created a conflict.

So on this line:

<CourseModelRegister HighSchoolRegistrationModelId="@HighSchoolRegistrationModelId"> 
</CourseModelRegister>

You don't need to pass HighSchoolRegistrationModelId a value, because it will be filled by the [CascadingParameter]. In your case, you might need to make sure your middle component also has a [CascadingParameter] for the value to be passed to its children.

answered Dec 17, 2021 at 14:06

Shuryno

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1 Comment

amdorsey12 Over a year ago

Taking the value out of that tag still resulted in the same error, sadly.

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