I have a ComboBox/DropDownList that gets data from a remote service, using virtualization. When the PageSize property is big enough (in my case 20), I have issues scrolling up the selection box dropdown list. I'm trying to scroll but then resets to the currently selected item making it almost impossible to scroll up. You can use your own demo examples to replicate this issue.

To reproduce the issue, try the ComboBox - Virtualization, in Telerik REPL (Demo), change the PageSize from 10 to 20. Open the dropdown and select an item. Then, open again the dropdown and scroll slowly up.

I would like to change the text in the ComboBox dropdown when there is no data in the source collection.

At the moment the only option is through localization for all instances like here.

Transitioning our application from Telerik React to Blazor, our comboboxes in our React application are hooked up to OData endpoints because of the amount of data they could display, some as large as 30mb of json.

Server filtering, https://feedback.telerik.com/blazor/1447481-server-filtering-with-custom-data-request-event-that-can-accommodate-remote-data, almost works, however:

• I can't set PageSize on the combobox
• I can't set TotalCount on the combobox
• Using Telerik.Blazor.ExtensionMethods.ToOdataString throws a NullReferenceException when I try to use it in the ReadItems method with the ComboBoxReadEventArgs args.Reqeuest.ToOdataString()

I tried setting up my combobox like my OData Grid, i.e.

<TelerikComboBox Data="@Dtos"
                         OnRead="@ReadItems"
                         Filterable="true"
                         Placeholder="Find what you seek by typing"
                         @bind-Value="@SelectedValue"
                         TextField="Name" 
                         ValueField="Id"
                         Pageable="true" 
                         PageSize="20" 
                         TotalCount=@Dtos.Count
                         >

However it throws an exception:

blazor.webassembly.js:1 WASM: System.InvalidOperationException: Object of type 'Telerik.Blazor.Components.TelerikComboBox`2[[MyType, MyNamespace, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[System.Guid, mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]' does not have a property matching the name 'Pageable'.

Was hoping this would 'just work' like it does with the Grid, which is amazing!

ComboBox value binding broken in 2.9.0, works fine in 2.8.0

Please see your own documentation example:

<TelerikComboBox Data="@MyList" @bind-Value="MyItem">
</TelerikComboBox>

@code {
    protected List<string> MyList = new List<string>() { "first", "second", "third" };
    protected string MyItem { get; set; } = "second";
}

The popup window is not closed when the ComboBox is disabled from code.

Reproduction code:

Selected value: @selectedValue
<br />

<TelerikComboBox Data="@myComboData"
                 TextField="MyTextField"
                 ValueField="MyValueField"
                 Value="selectedValue"
                 ValueChanged="@((int value) => ValueChangedHandler(value))"
                 Placeholder="Select an item..."
                 ClearButton="true"
                 Enabled="@isEnabled"
                 Filterable="true">
</TelerikComboBox>

@code {
    public bool isEnabled { get; set; } = true;
    IEnumerable<MyDdlModel> myComboData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });

    int selectedValue { get; set; } = 3; //usually the current value should come from the model data

    public async Task ValueChangedHandler(int value)
    {
        isEnabled = false;
        await Task.Delay(4000); //simulate network delay

        selectedValue = value;

        isEnabled = true;
    }

    //in a real case, the model is usually in a separate file
    //the model type and value field type must be provided to the dropdpownlist
    public class MyDdlModel
    {
        public int MyValueField { get; set; }
        public string MyTextField { get; set; }
    }
}

When selecting an item with the Enter key, the value is not displayed in the input field.

1. Open this REPL example
2. Open the ComboBox and navigate with the arrows to any item
3. Hit "Enter" to select the item

The item is selected, but its value is not displayed inside the input field.

===

The issue is also reproducible with the MultiColumnComboBox component. 

Hi,

If I enter some characters in the ComboBox to filter it, the characters that I enter aren't shown and the filtering is not correct. Indeed, if I enter "ALU" (some of my data start with "ALU", no data appears.

In my data, I have multiple identical values for the TextField of the ComboBox. When the user selects one of them and focuses away from the component the selected value changes to the first instance of the items with the same TextFields, although they have different ValueFields.

Reproduction:

<TelerikComboBox Data="@myDdlData" 
                 TextField="MyTextField" 
                 ValueField="MyValueField" 
                 Value="selectedValue" 
                 ValueChanged="@((int? id) => ValueChangedHandler(id))" 
                 FilterOperator="StringFilterOperator.Contains"
                 Filterable="true">
</TelerikComboBox>

@code {
    private List<MyDdlModel> myDdlData { get; set; }

    private void ValueChangedHandler(int? id)
    {
        selectedValue = id;
    }

    public class MyDdlModel
    {
        public int? MyValueField { get; set; }
        public string MyTextField { get; set; }
    }

    int? selectedValue { get; set; }

    protected override void OnInitialized()
    {
        myDdlData = new List<MyDdlModel>()
        {
            new MyDdlModel()
            {
                MyValueField = 1,
                MyTextField = "John Smith"
            },
            new MyDdlModel()
            {
                MyValueField = 2,
                MyTextField = "John Smith"
            },
            new MyDdlModel()
            {
                MyValueField = 3,
                MyTextField = "John Smith"
            },
            new MyDdlModel()
            {
                MyValueField = 4,
                MyTextField = "Alice Jones"
            },
            new MyDdlModel()
            {
                MyValueField = 5,
                MyTextField = "Alice Jones"
            },
        };
    }
}

Replication code:

@SelectedValue
<br />
<TelerikComboBox Data="@DdoData"
                 OnRead="@OnReadHandler"
                 Filterable="true"
                 ValueField="RecId"
                 TextField="DdoTitle"
                 Placeholder="Find what you seek by typing"
                 @bind-Value="@SelectedValue">
</TelerikComboBox>

@code{
    public int SelectedValue { get; set; } = 4;
    List<ddo> DdoData { get; set; }
    public string ddoCbType { get; set; } = "Default";
    int InitialId { get; set; }
    string currentText { get; set; } = "";

    protected override async Task OnInitializedAsync()
    {
        await ReadDdoData(ddoCbType, "");
        if (SelectedValue > 0)
        {
            InitialId = (int)SelectedValue;
            await ReadDdoData(ddoCbType, currentText);
        }
    }

    async Task OnReadHandler(ComboBoxReadEventArgs args)
    {
        if (args.Request.Filters.Count > 0)
        {
            Telerik.DataSource.FilterDescriptor filter = args.Request.Filters[0] as Telerik.DataSource.FilterDescriptor;
            currentText = filter.Value.ToString();
            await ReadDdoData(ddoCbType, currentText);
        }
        else
        {
            currentText = "";
            await ReadDdoData(ddoCbType, "");
        }
    }

    private async Task ReadDdoData(string ddoCbType, string currentText)
    {
        await Task.Delay(100);

        DdoData = new List<ddo>()
        {
                new ddo(){ RecId = 1, DdoTitle = "one"},
                new ddo(){ RecId = 2, DdoTitle = "two"},
                new ddo(){ RecId = 3, DdoTitle = "Three"},
                new ddo(){ RecId = 4, DdoTitle = "Four"},
                new ddo(){ RecId = 5, DdoTitle = "Five"}
            };

        //this does not help
        await InvokeAsync(StateHasChanged);
    }

    public class ddo
    {
        public int RecId { get; set; }
        public string DdoTitle { get; set; }
    }
}

When the height of the popup is set to 'auto' and it opens upwards, the resizing process causes it to be incorrectly positioned.

# Reproduction:

1. Open this REPL - https://blazorrepl.telerik.com/mHuoPRFk52ienlUt52
2. Shrink the browser so that the ComboBox remains at the bottom of the window: 


3. Type "item 2" in the ComboBox

When i search for something by typing in combobox, i want to be able to use the keyboard to make my selection

Exable below, if i press b, I want to be able to either select baseboll by pressing enter, or make another selection by using arrow keys and then enter. 

Issue - Setting the selected element of a combo box inside a form worked in 2.22.0 and no longer works in 2.23.0 

Repo - https://github.com/benhysell/BlazorGridPagingIssue

Steps to Reproduce 

• In the test repo start the application and navigate to https://localhost:5001/updateWeather
• The selected value in the combo box should be the 8th value, "summary 8"
• Stop the application, in BlazorGrid.Client.csproj 
  • Replace <PackageReference Include="Telerik.UI.for.Blazor" Version="2.22.0" />
  • With <PackageReference Include="Telerik.UI.for.Blazor" Version="2.23.0" />
• Do a clean/rebuild to ensure the latest version of Telerik Blazor is being used
• Run the application in a new incognito window and navigate back to https://localhost:5001/updateWeather, notice how nothing is selected in the combo box

Details

This is a contrived example pulled out of a larger application.  Almost all of our combo boxes are backed by OData calls.  When we 'create or POST' an element the first time we load the form we have the combo box make an OData call to retrieve the top 200 elements.  On a subsequent 'edit or PUT', where we have a thing we want to update we first go get the thing we want to work with, and then fill in the comobo box with that element.

In this example application we simulate this load by deciding if a value was passed in or not for the combo box.  https://localhost:5001/updateWeather always passes in an 8 to load the 8th element.  https://localhost:5001/createWeather does not pass in any value, leaving the form value unbound.

This all worked as expected in 2.22.0, however once we upgraded to 2.23.0 we could no longer set the value of the combo box on load when combined with an OData call.

A ComboBox is databound via OnRead. It has an initial value, but no data arrives after the first OnRead call. We call Rebind() to fetch data and then it populates, but the component value doesn't show.

Click the button. The ComboBox should show its initial value, but doesn't. A similar scenario worked until version 2.30, when there was no Rebind(), but we set Data directly.

The workaround is to set raise a flag in OnRead and set the value in OnAfterRenderAsync.

@using Telerik.DataSource.Extensions

<TelerikButton OnClick="@BindCombo">Rebind Combo</TelerikButton>

<TelerikComboBox TItem="@ComboItem"
                 TValue="int"
                 @ref="@ComboRef"
                 TextField="Text"
                 ValueField="Id"
                 OnRead="OnComboRead"
                 Width="200px"
                 @bind-Value="@ComboValue">
</TelerikComboBox>

@code {
    string FilterValue { get; set; } = "A";
    int ComboValue { get; set; } = 2;
    bool BindFlag { get; set; }
    bool ShouldResetValue { get; set; }
    IEnumerable<ComboItem> LegacyComboData { get; set; }

    TelerikComboBox<ComboItem, int> ComboRef { get; set; }

    void BindCombo()
    {
        BindFlag = true;
        ComboRef.Rebind();
    }

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (ShouldResetValue)
        {
            // comment out the initially set value above to make the following line work
            ComboValue = 2;
            StateHasChanged();
        }

        await base.OnAfterRenderAsync(firstRender);
    }

    async Task OnComboRead(ComboBoxReadEventArgs args)
    {
        if (BindFlag)
        {
            var service = new MyService();

            var data = await service.GetComboItem(FilterValue);
            var result = await data.ToDataSourceResultAsync(args.Request);

            args.Data = result.Data;

            //ShouldResetValue = true;
        }
    }

    public class ComboItem
    {
        public int Id { get; set; }
        public string Code { get; set; }
        public string Text { get; set; }
    }

    public class MyService
    {
        public async Task<IEnumerable<ComboItem>> GetComboItem(string code)
        {
            await Task.Delay(300);

            var data = new[]
            {
                    new ComboItem{ Id = 1, Code = "A", Text = "ValueA1" },
                    new ComboItem{ Id = 2, Code = "A", Text = "ValueA2" },
                    new ComboItem{ Id = 3, Code = "A", Text = "ValueA3" },
                    new ComboItem{ Id = 4, Code = "B", Text = "ValueB4" },
                    new ComboItem{ Id = 5, Code = "B", Text = "ValueB5" },
                    new ComboItem{ Id = 6, Code = "B", Text = "ValueB6" },
                    new ComboItem{ Id = 7, Code = "C", Text = "ValueC7" },
                    new ComboItem{ Id = 8, Code = "C", Text = "ValueC8" },
                    new ComboItem{ Id = 9, Code = "C", Text = "ValueC9" },
                };

            return data.Where(x => x.Code == code).ToList();
        }
    }
}

When I select an item from the combo box dropdown, the OnChange event fires with the new value, but the model field is not updated yet.

@selectedValue

<TelerikComboBox Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField"
                 @bind-Value="@selectedValue"  OnChange="@MyOnChangeHandler">
</TelerikComboBox>

@code {
    int selectedValue { get; set; }

    IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });
    
    private void MyOnChangeHandler(object theUserInput)
    {
        Console.WriteLine($"COMBO: the models is now {selectedValue} and the handler received {theUserInput}");
    }

    public class MyDdlModel
    {
        public int MyValueField { get; set; }
        public string MyTextField { get; set; }
    }
}

The ComboBox will not display an initial selected item, if the value is equal to the type's default. Applies to integers, guids, etc.

This used to work until version 2.30.

Here is a REPL test page.

If the value type is nullable, a zero int value will work for initial item selection.

I want to capture the user selection (which has to happen through ValueChanged, as OnChange does not fire when I need it). At this point I want to use the selection from the user and to clear the combo box.

I would expect that this should work but it does not:

@result
<br />
from model: @MyItem
<br />
<br />
<TelerikComboBox Data="@MyList" Value="@MyItem" ValueChanged="@( (string v) => MyValueChangeHandler(v) )" Placeholder="Choose something">
</TelerikComboBox>

@code {
    string result;
    private async Task MyValueChangeHandler(string theUserChoice)
    {
        result = string.Format("The user chose: {0}", theUserChoice);

        MyItem = null; // this should be enough

    }
    protected List<string> MyList = new List<string>() { "first", "second", "third" };
    protected string MyItem { get; set; } = "second";
}

If my browser culture is set to Swedish, I can no longer tab through multiple ComboBoxes.

<AdminEdit>

You can manually add the TabIndex parameter to each ComboBox and set their values to non-negative integers.

</AdminEdit>