How to pass a value into partial tag helper? (ASP.NET Core)

Question

I'm trying to render a partial view inside a form, I need to use the value of the loop (+1 of course because it starts at 0) as one of the values in my partial, any ideas how I can make this work?

I've tried to do this with ViewData or ViewBag but either this is the wrong method or I'm implementing it wrong

Here is my main form:

@model Measurement

<form asp-action="Create" method="post">
    <div class="form-group" hidden>
        <label asp-for="LymphSiteId"></label>
        <input asp-for="LymphSiteId" [email protected] />
        <span asp-validation-for="LymphSiteId"></span>
    </div>
    <div class="form-group" hidden>
        <label asp-for="UserId"></label>
        <input asp-for="UserId" value="1" />
        <span asp-validation-for="UserId"></span>
    </div>
    <div class="form-group">
        <label asp-for="MeasurementDate"></label>
        <input asp-for="MeasurementDate" />
        <span asp-validation-for="MeasurementDate"></span>
    </div>

    @for (int i = 0; i < ViewBag.NumMeasuringPoints; i++)
    {
        <partial name="_New" view-data=@(i+1) />
    }
    <button type="submit">Submit</button>
</form>

Here is my partial:

@model Circumference
    <div class="form-group" hidden>
        <input asp-for="Id" />
    </div>
    <div class="form-group" hidden>
        <input asp-for="MeasurementId" value="@ViewBag.Id" />
    </div>
    <div class="form-group">
        <label asp-for="PositionFromStart">Position from Start</label>
        <input asp-for="PositionFromStart" value="@ViewData" />
    </div>
    <div class="form-group">
        <label asp-for="DistanceAround">Circumference at point (cm)</label>
        <input asp-for="DistanceAround" />
    </div>

Any help greatly appreciated - thanks!

Answer 1

I'm trying to render a partial view inside a form, I need to use the value of the loop (+1 of course because it starts at 0) as one of the values in my partial, any ideas how I can make this work?

You can try to modify the code like below to assigns a ViewDataDictionary to pass to your partial view.

In main form

@for (int i = 0; i < ViewBag.NumMeasuringPoints; i++)
{
    ViewData["PositionFromStart"] = i + 1;

    var pmodel = new Circumference();

    <partial name="_New" model="pmodel" view-data="ViewData" />
}

In partial view

@model Circumference

<div class="form-group" hidden>
    <input asp-for="Id" />
</div>
<div class="form-group">
    <input asp-for="MeasurementId" value="@ViewBag.Id" />
</div>
<div class="form-group">
    <label asp-for="PositionFromStart">Position from Start</label>
    <input asp-for="PositionFromStart" value="@ViewData["PositionFromStart"]" />
</div>
<div class="form-group">
    <label asp-for="DistanceAround">Circumference at point (cm)</label>
    <input asp-for="DistanceAround" />
</div>