Documentation for Addon to contain Validation info

[oaldrian]

Is your feature request related to a problem? Please describe.
When working with Addon and Validation, there are a few extra steps to take to make it visually "correct".
These are described in #4106

Describe the solution you'd like
The solution (or a different one, that has a similar result) of #4106 should be added to the Addon docs, as apart from this issue the info is not easily available.

[sturlath]

I guess this “solves” this one #3802 right?

[stsrki]

@sturlath Yes, it should work with #3802. But you will have to adjust the Addons structure according to the documentation example.

[sturlath]

@stsrki Just tried this with 1.3.1 and this code here does not work. And I can´t see better than your validation example doesn´t either..

<Column>
    <Field>
        <FieldLabel>@L["StartingDate"]</FieldLabel>
        <Validation Validator="@ValidateEventStartingDate">
            <Addons>
                <Addon AddonType="AddonType.Body">
                    <DatePicker @ref="@startingDatePicker" TValue="DateTime?" InputMode="DateInputMode.Date" Date="@NewStreamEvent.StartingDate" DateChanged="@OnStartingDateChanged" DisplayFormat="dd-MM-Y" Disabled="@DisabledMode">
                    </DatePicker>
                </Addon>
                <Addon AddonType="AddonType.End">
                    <Button Color="Color.Light" Clicked="@(()=>startingDatePicker.ToggleAsync())">
                        <Icon Name="IconName.CalendarDay" />
                    </Button>
                </Addon>
            </Addons>
            <ValidationNone></ValidationNone>
            <ValidationSuccess></ValidationSuccess>
            <ValidationError>@L["PleaseSelectValidFutureStartingDateForEventDate"]</ValidationError>
        </Validation>
    </Field>
</Column>

  private void ValidateEventStartingDate(ValidatorEventArgs e)
  {
      if (StartingDateInPastNotAllowed)
      {
          if (!NewStreamEvent.StartingDate.HasValue || NewStreamEvent.StartingDate.Value.DayOfYear < Clock.Now.DayOfYear)
          {
              e.Status = ValidationStatus.Error;
          }
          else
          {
              e.Status = ValidationStatus.Success;
          }
      }
  }