Blazor Invoking null

Question

I have a small but interesting problem which I can't wrap my head around. I have a custom DatePicker component which uses TValue as Value (generic, you can pass DateTime or DateTime? as TValue). And inside a calendar I have button 'x' which clears the Value to default of TValue

    [Parameter]
    public EventCallback<TValue> ValueChanged { get; set; }
    
    protected async void ClearInputData()
    {
        await ValueChanged.InvokeAsync(default(TValue));
        Value = default(TValue);
        selectedHour = 0;
        selectedMinute = 0;
        selectedSecond = 0;
        OnInput?.Invoke();
    }

The problem is that default(TValue) if TValue == DateTime is null, and you cannot invoke null; What could be the smartest way ot getting around this?

but the place where I invoke that value I need to know that the value is unselected. For example, I have typed 2020-06-06, and when I press x I need to inform my other component, that the value now is null — Povilas Dirse
– Povilas Dirse, Commented Jun 30, 2021 at 13:32
Start by making it an async Task method and see if the problem persists. If so, post exact error messages or other results. — Henk Holterman
– Henk Holterman, Commented Jun 30, 2021 at 14:46
Ah, I found the problem. It was a deeper problem. I'm also using custom grid, and inside inserting template I was using ValueChanged=((args) => data.Date = args.Value). And args was null and Value would crash... Sorry for such a dumb error, that's totally my bad... Lesson learn, debug your code deeper — Povilas Dirse
– Povilas Dirse, Commented Jun 30, 2021 at 20:03

Caveman74 · Accepted Answer · 2021-08-03 15:38:35Z

2

I tried to reproduce your problem.

My DateComponent:

    <h3>DateComponent</h3>
    
    @typeparam TValue
    <p>Value: @Value</p>
    <button @onclick="() => ClearInputData()">X</button>
    
    @code {
        [Parameter]
        public EventCallback<TValue> ValueChanged { get; set; }
    
        [Parameter]
        public TValue Value { get; set; }
    
        protected async Task ClearInputData()
        {
            await ValueChanged.InvokeAsync(default(TValue));
            Value = default(TValue);
        }
    }

My consumer:

    <DateComponent TValue="DateTime?" @bind-Value="@Value1"></DateComponent>
    <p>@(Value1.HasValue ? Value1 : "(null)")</p>
    
    <DateComponent TValue="DateTime" @bind-Value="@Value2"></DateComponent>
    <p>@Value2</p>
    
    @code {
        DateTime? Value1 { get; set; } = DateTime.Now;
        DateTime Value2 { get; set; } = DateTime.Now;
    }

In my example, everything works as expected. Did I miss something?

edited Aug 3, 2021 at 15:38

answered Jun 30, 2021 at 15:11

Caveman74

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5 Comments

Henk Holterman Over a year ago

Can you try again with async void ClearInputData() ?

Povilas Dirse Over a year ago

Mhm.... Okey, I will try to implement, maybe my problem might be on the other end

Povilas Dirse Over a year ago

Worked like a charm. A problem was because of void, Task fixed it. EDIT: I found, my other component was the problem. I think that datepicker component was working as it should, but my custom grid was getting an error here

Caveman74 Over a year ago

@HenkHolterman: It doesn't matter whether void or task is returned.

Henk Holterman Over a year ago

Leave the Task in anyway. Just for coy/pasters.

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