---
ADMIN EDIT
Here is a reproducible with the workaround highlighted in green:
@using System.Collections.ObjectModel
<h4>Option Selected: 6 @selectedSix</h4>
<br />
<TelerikDropDownList Data="@myDdlData"
TextField="MyTextField"
ValueField="MyValueField"
@bind-Value="@selectedSix" />
<h4>Option Selected: 7 @selectedSeven</h4>
<br />
<TelerikDropDownList Data="@myDdlData"
TextField="MyTextField"
ValueField="MyValueField"
@bind-Value="@selectedSeven">
</TelerikDropDownList>
<TelerikButton OnClick="@AddOption">Add Item</TelerikButton>
<ul>
@foreach (var item in myDdlData)
{
<li>@item.MyValueField</li>
}
</ul>
@code {
int selectedSix { get; set; } = 6;
int selectedSeven { get; set; } = 7;
ObservableCollection<MyDdlModel> myDdlData = new ObservableCollection<MyDdlModel>(Enumerable.Range(1, 5).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x }));
protected override async Task OnInitializedAsync()
{
AddOption();
await Task.Delay(TimeSpan.FromSeconds(1));
AddOption();
}
void AddOption()
{
myDdlData.Add(new MyDdlModel { MyTextField = "item " + (myDdlData.Count + 1), MyValueField = myDdlData.Count + 1 });
int origSelection = selectedSeven;
selectedSeven = 0;
StateHasChanged();
//add this if it does not work
//await Task.Delay(30);//wait a rendering frame
selectedSeven = origSelection;
//add this if it does not work
//StateHasChanged();
}
public class MyDdlModel
{
public int MyValueField { get; set; }
public string MyTextField { get; set; }
}
}
Note: This behavior also occurs if the initial data is received after the component is initialized. The workaround in this case will be similar - set the selected value after the data is received.
---
In TelerikSelectBase that the DropDownList inherits, the FieldIdentifier is set only in the OnInitializedAsync method and therefore the FieldIdentitier is never updated. This can cause issues with validation as seen in this example: https://blazorrepl.telerik.com/GyamPdlf37LXpPAW36.
To reproduce:
For reference, in the TelerikInputBase, the FieldIdentifier is set in the SetParameterAsync and thus it is accordingly updated. See the TextBox behavior in the above sample.
When used in Bootstrap Grid the DropDownList popup is misaligned on the first open. On a second click, it is aligned.
This behavior is also valid for Combobox and Autocomplete.
Reproduction code:
<div class="box">
<div class="row mt-3" style="align-items:center">
<div class="col-12 col-lg-4">
<span class="bold">ComboBox</span>
</div>
<div class="col">
<TelerikComboBox Data="@myComboData" TextField="ComboTextField" ValueField="ComboValueField"
@bind-Value="selectedCombo" ClearButton="true" Filterable="true">
</TelerikComboBox>
</div>
</div>
<div class="row mt-3" style="align-items:center">
<div class="col-12 col-lg-4">
<span class="bold">DropDownList</span>
</div>
<div class="col">
<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField"
@bind-Value="@selectedDropDown">
</TelerikDropDownList>
</div>
</div>
<div class="row mt-3" style="align-items:center">
<div class="col-12 col-lg-4">
<span class="bold">Autocomplete</span>
</div>
<div class="col">
<TelerikAutoComplete Data="@Suggestions" @bind-Value="@AutoCompleteValue"
ClearButton="true" />
</div>
</div>
</div>
@code {
public int selectedDropDown { get; set; }
public int selectedCombo { get; set; }
public string AutoCompleteValue { get; set; }
//ComboBox
public class ComboModel
{
public int ComboValueField { get; set; }
public string ComboTextField { get; set; }
}
IEnumerable<ComboModel> myComboData = Enumerable.Range(1, 20).Select(x => new ComboModel { ComboTextField = "item " + x, ComboValueField = x });
//DropDownList
public class MyDdlModel
{
public int MyValueField { get; set; }
public string MyTextField { get; set; }
}
IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });
//Autocomplete
List<string> Suggestions { get; set; } = new List<string> {
"Manager", "Developer", "QA", "Technical Writer", "Support Engineer", "Sales Agent", "Architect", "Designer"
};
}
---
ADMIN EDIT
This behavior is observed in the DropDownList when filtering is enabled and in the ComboBox regardless of whether filtering is enabled or not.
The (filter) input gets focus, which shows the soft keyboard, which changes the viewport size, which causes the dropdown to hide. Unfortunately, there is no workaround at the moment (except perhaps disabling filtering for small viewports).
---
I have a cascading DropDownList scenario with virtual scrolling. When the first DropDownList changes value, the second one should reset its scrollbar to the top, because it now contains new data. This doesn't happen.
Here is a REPL test page.
===
ADMIN EDIT
===
As a workaround for the time being, you may track when the value is changed in the parent DropDownList to dispose and re-initialize the child DropDownList.
Here is an example: https://blazorrepl.telerik.com/mdafHabk585ZtzyV54.
Before, the Value from the first item in the Data was populated through @bind-Value to the view model. It no longer is.
In the following snippet, I expect to see "1" in the initial load of the page, but I see "0" - the default value for the integer.
@selectedValue
<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="@selectedValue">
</TelerikDropDownList>
@code {
//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; }
}
IEnumerable<MyDdlModel> myDdlData = Enumerable.Range(1, 20).Select(x => new MyDdlModel { MyTextField = "item " + x, MyValueField = x });
int selectedValue { get; set; }
}
The following knowledge base article describes how to select the default value in a drop down, but if there's no default value the selection is not cleared using this method.
When setting the bind value to null (or the default, or frankly anything that doesn't exist in the drop down) I'd like the drop down list selection to be cleared when there's no default value set on the DropDownList.
@page "/"
<br />
<TelerikButton OnClick="@ClearSelection">Clear selection</TelerikButton>
<TelerikDropDownList Data="@data" @bind-Value="selectedValue" />
@code {
List<string> data = new() { "selection" };
string selectedValue;
void ClearSelection()
{
// This does not cause the drop down to clear the selection and I think it should.
selectedValue = null;
}
}
Steps to reproduce:
Expected: the group name should change to "Seafood".
Actual: the group name is still "Beverages".
When the Value you bind to the DropDownList is null (for example, because it is a model that is not filled in by the user yet, and you need to perform validation), the component throws a null reference exception.
This does not happen for a nullable integer (example here)
Reproducible:
@
using
System.ComponentModel.DataAnnotations
@
using
Telerik.Blazor.Components.DropDownList
<EditForm Model=
"@PageData"
OnValidSubmit=
"@HandleValidSubmit"
>
<DataAnnotationsValidator />
<ValidationSummary />
@PageData.QuoteState
<TelerikDropDownList bind-Value=
"@PageData.QuoteState"
DefaultItem=
"@Hint"
Width=
"300px"
Data=
"@states"
TextField=
"stateName"
ValueField=
"stateID"
>
</TelerikDropDownList>
<ValidationMessage For=
"@(() => PageData.QuoteState)"
></ValidationMessage>
<button type=
"submit"
>Submit</button>
</EditForm>
@functions {
public
MyViewModel PageData {
get
;
set
; } =
new
MyViewModel();
public
statesModel Hint {
get
;
set
; } =
new
statesModel { stateID =
null
, stateName =
"Not Selected"
};
public
class
statesModel
{
public
string
stateID {
get
;
set
; }
public
string
stateName {
get
;
set
; }
}
public
class
MyViewModel
{
[Required(ErrorMessage =
"State is mandatory."
)]
//the value field in the dropdown model must be null in the default item
public
string
QuoteState {
get
;
set
; }
}
public
IEnumerable<statesModel> states =
new
List<statesModel>
{
new
statesModel { stateID =
"ACT"
, stateName =
"ACT"
},
new
statesModel { stateID =
"NSW"
, stateName =
"NSW"
},
new
statesModel { stateID =
"NT"
, stateName =
"NT"
},
new
statesModel { stateID =
"QLD"
, stateName =
"QLD"
},
new
statesModel { stateID =
"SA"
, stateName =
"SA"
},
new
statesModel { stateID =
"TAS"
, stateName =
"TAS"
},
new
statesModel { stateID =
"VIC"
, stateName =
"VIC"
},
new
statesModel { stateID =
"WA"
, stateName =
"WA"
}
};
void
HandleValidSubmit()
{
Console.WriteLine(
"OnValidSubmit"
);
}
}
TlerikDropDownList keyboard navigation works differently from native html select.
In case we have a list with many similar options, for example:
011
021
211
....
In this case with native html select I can type 02 to select 021, but with TlerikDropDownList this would select 211.
If you type swiftly multiple printable characters, the DropDownList keyboard navigation will react only to the first character.
Clicking on the <label> opens the dropdown, but clicking on its main element does not
Selected value: @selectedValue
<br />
<label>some label for the dropdown, open it and test whether clicking outside closes it
<TelerikDropDownList Data="@myDdlData" TextField="MyTextField" ValueField="MyValueField" @bind-Value="selectedValue">
</TelerikDropDownList>
</label>
@code {
//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; }
}
IEnumerable<MyDdlModel> myDdlData = 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
}