asp.net core - Property values of the same type are updated incorrectly in Blazor

Question

Background:

I wanted to achieve the following:

1. Keep a copy of the data context and use the copy for editing
2. So that I can reset the data context back to its unchanged state using an onclick event by doing copyValue = unchangedValue

Here is my attempt (it's been trimmed down in size to reduce noises but it has the same issue):

**index.razor**

@page "/"
@using SolutionName.Data
@using System.Reflection

<EditForm Model="Items2">
    <table class="table">
        <thead>
            <tr>
                <th>Summary</th>
            </tr>
        </thead>
        <tbody>
            @foreach (var i in Items2)
            {
                <tr @key="@i.GetHashCode()">
                    <InputText @bind-Value="i.Summary"></InputText>
                </tr>
            }
        </tbody>
    </table>
</EditForm>



//
//reflections for debuggings
//
@if (Items != null)
{
    <p>
        @foreach (var item in Items)
        {
            <span>@($"Items.{typeof(WeatherForecast).GetProperty(nameof(WeatherForecast.Summary)).Name}={typeof(WeatherForecast).GetProperty(nameof(WeatherForecast.Summary)).GetValue(item)}")</span>
        }
    </p>
}
@if (Items2 != null)
{
    <p>
        @foreach (var item in Items2)
        {
            <span>@($"Items2.{typeof(WeatherForecast).GetProperty(nameof(WeatherForecast.Summary)).Name}={typeof(WeatherForecast).GetProperty(nameof(WeatherForecast.Summary)).GetValue(item)}")</span>
        }
    </p>
}


@code{
    List<WeatherForecast> Items = new List<WeatherForecast>();

    List<WeatherForecast> Items2 = new List<WeatherForecast>();
    protected override void OnInitialized()
    {
        Items = new List<WeatherForecast>()
        {
            new WeatherForecast()
            {
                Date = DateTime.Now,
                Summary = "123",
                TemperatureC = 1
            }
        };
        Items2 = Items;
    }
    private void ResetItems2()
    {
        Items2 = Items;
    }
}

As you can see, I am binding Items2, and not Items, to the <EditForm>. However, updating the summary seems to update both Items2 and Items. I also noticed that this will not happen if Items and Items2 are of two different types (say that they have exactly the same properties, and I cast one to another...)

Two questions:

Why is Item updated in this case?

Is there a way to only update Items2 and not Items, while allowing Items and Items2 to be the same type?

Detailed steps to reproduce the issue:

Step 1. Initialized and render for the first time

Step 2. Change the value to 456 and then tab away

The expected result should be

Items.Summary=123 (not 456)

Items2.Summary=456

Answer 1

The issue is that you're using reference type assignment. When you assign Items to Items2, you actually assign a pointer to Itemss values. Both variable point to the same list of objects.

If it's applicable create a value type instead. Saving data in the local storage and then retrieving it is a viable solution.

This:

List<WeatherForecast> Items = new List<WeatherForecast>();

List<WeatherForecast> Items2 = new List<WeatherForecast>();

is superfluous. Code like this:

List<WeatherForecast> Items;

List<WeatherForecast> Items2;