RadzenListBox, bug when using asynchronous call LoadData

Radzen.Blazor Components
#1

Hi team,

when using an HttpClient and set Multiple selection property true and AllowVirtualization [RadzenListBox],
throws an hard exception.

Error: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.Collections.Generic.List1.Enumerator.MoveNext()* *at System.Linq.Enumerable.SelectListIterator2.MoveNext()
at System.Linq.Enumerable.CastIterator[TResult](IEnumerable source)+MoveNext()
*at Radzen.DropDownBase`1.SelectItemFromValue(Object value) *
in ...\radzen-blazor\Radzen.Blazor\DropDownBase.cs:line 950

It tries to change the list in the same time as the list is read.
A quick fix would be to copy the list.

//Change from
foreach (object v in values)

//To
foreach (object v in values.ToList())

The method name is "SelectItemFromValue(object value)" in "DropDownBase" class

But this is not a clean solution.
I unfortunately do not have time for a clean solution and pull request
I hope the bug can be fixed quickly.

As an example:

<h4>Virtualization using LoadData event</h4>
<RadzenListBox AllowVirtualization="true" 
    Multiple="true"
    AllowFiltering="true" 
    Count="@count" 
    LoadData=@LoadDataVirtualization 
    Data=@attributesDataVirtualization
    TextProperty="Name"
    ValueProperty="Name"
    @bind-Value=@attributeValues
    Style="height:200px" Class="w-100" />

IEnumerable<string> attributeValues = new string[] {  };

async Task LoadDataVirtualization(LoadDataArgs args)
{
    var pagedResult = await GetAttributesAsync(args.Skip.HasValue ? args.Skip.Value : 0, args.Top.HasValue ? args.Top.Value : 10);

    count = items.Count;

    attributesDataVirtualization = pagedResult.Results;

    //var query = dbContext.Customers.AsQueryable();

    //if (!string.IsNullOrEmpty(args.Filter))
    //{
    //    query = query.Where(c => c.CustomerID.ToLower().Contains(args.Filter.ToLower()) || c.ContactName.ToLower().Contains(args.Filter.ToLower()));
    //}

    //console.Log($"LoadData with virtualization: Skip:{args.Skip}, Top:{args.Top}, Filter:{args.Filter}");

    //count = query.Count();

    //customCustomersDataVirtualization = query.Skip(args.Skip.HasValue ? args.Skip.Value : 0).Take(args.Top.HasValue ? args.Top.Value : 10).ToList();

    //InvokeAsync(StateHasChanged);
}

I have tested this directly in the Radzen demo (repo)

@Parijsy
There is probably a similar problem but I am not sure
RadzenListBox with Multiple and Virtualization

-Tom

#2

I have looked at this now.
The problem with asynchronous processing is the two-way binding value property.

At the same time a value is set multiple and read by forearch.
This triggers the exception.

@bind-Value=@values

DataBoundFormComponent<T> CLASS
[Parameter]
public object Value
{
    get
    {
        return _value;
    }
    set
    {
        if (_value != value)
        {
            _value = object.Equals(value, "null") ? null : value;
        }
    }
}

FIX
DropDownBase<T> CLASS
protected virtual void SelectItemFromValue(object value)
{
    if (value != null && View != null)
    {
        if (!Multiple)
        {
            //......
        }
        else
        {   
             /*NEW*/                  
            var values = value as IEnumerable<object>;
            /*CURRENT*/
            //var values = value as dynamic;
            if (values != null)
            {
                if (!string.IsNullOrEmpty(ValueProperty))
                {
                    /*NEW*/   
                    foreach (object v in values.ToArray())
                    /*CURRENT*/
                    //foreach (object v in values)
                    {
                       //......
                    }
                }
                else
                {
                       //......
                }
            }
        }
    }
    else
    {
        selectedItem = null;
    }
}

It is accessed read only you can make a shallow copy with ToArray().
It solves the problem.

I hope it is helpful.

-Tom

#3

Hi @Tom,

We would need a reproduction of this issue. How can we get this exception by modifying the RadzenListBox online demo?

#4

@korchev
Hi, can you invite me to github and I could create a branch and commit it ?
If that's ok?

You can get my email from my account here I think.

-Tom

#5

I can't invite you to github however you can open a pull request without an invitation. Still we prefer to reproduce the issue first hence my request.

#6

@korchev

No problem.
In the startup of the demo add the client.

services.AddHttpClient();

Then just replace the ListBoxPage and start the demo.

ListBoxPage.zip (1.9 KB)

Select the entries of the ListBox you want and scroll up and down.
Then the exception is thrown.

ListBox
ListBox1654×1106 161 KB

-Tom

#7

We've fixed this and the fix will be part of our next update before the end of the week.

1 Like
#8

@enchev
Good morning, this is fanatstic news.
I noticed that multipleValues has double entries after scrolling up and down when items are selected.

If there is time it would be great if this could be fixed.

@bind-Value="multipleValues"

-Tom

#9

@enchev

I have seen that it was fixed in the master branch.
Many thanks for the fast and professional work.

I have found another bug as written before.
After scrolling up and down the list of selected items is getting bigger.

For example: Two items selected, after scrolling there are 5

I added that in my example before.

ListBoxPage.zip (2.0 KB)

ListBoxSelectedItemsCount
ListBoxSelectedItemsCount551×1050 45 KB

It is about the list of values that is bound to the listbox.

@bind-Value=@multipleEntryValues
IEnumerable<string> multipleEntryValues = new string[] { };

-Tom

#10

Yes, we reproduced the problem. Hopefully fix for this will be released tomorrow with our next update.

#11

@enchev
Super fast your response really incredible :ok_hand:t3:
If my colleagues were sooo fast :wink:

-Tom

#12

@enchev
I have to bother you again :face_with_diagonal_mouth:

After scrolling up and down, you can no longer deselect the items.

-Tom

#13

We've just released update of Radzen.Blazor with your reports addressed.

#14

I have seen :ok_hand:t3:
Thanks a lot

-tom

#15

Hello Team,

i have found another bug and a performance leak.
Should I open a new topic or can I write it here?

-Tom

#16

It’s ok to continue here!

1 Like
#17

About the bug:

When the second dataset is loaded after scroll down, the select all checkbox is not deselected until I select an item from the list. Sometimes it works but usually it does not work.

Sometimes the behavior is also different.
Is difficult to explain :face_with_spiral_eyes:

Example:
SecondDataSet
SecondDataSet2

-Tom

#18

@enchev
Hi Enchev,

have you had the time to reproduce this?
Or do you need something from me to reproduce it?

-Tom

#19

I didn’t have time to look at this issue, I’ll try to check it this week.

#20

I've tried to reproduce this however select/deselect all worked normally:
dddg-sdall