DropDownList Data Binding
This article explains the different ways to provide data to a DropDownList component, the properties related to data binding and their results.
For details on Value Binding and Data Binding, and the differences between them, see the Value Binding vs Data Binding article.
There are two key ways to bind data:
There are also some considerations you may find useful, such as showing the DefaultText when the value is out of the data source range:
Strings or Value Types
You can data bind the DropDownList to a collection of string or value type data (such as int, decimal, bool, and Enum). When you have a concrete list of options for the user to choose from, their string representation is often suitable for display and you do not need special models.
- Provide an
IEnumerable<TItem>of the desired type to itsDataproperty. - Set a corresponding
Value. If theValueisnull, it will be populated with the first item from the data source.
Data binding a DropDownList to strings
<TelerikDropDownList Data="@DropDownListData" @bind-Value="DropDownListValue" />
@code {
private List<string> DropDownListData = new List<string>() { "first", "second", "third" };
private string DropDownListValue { get; set; } = string.Empty;
protected override void OnInitialized()
{
DropDownListValue = "second";
}
}
Bind to a Model
You can bind the DropDownList to a model in your application. This is useful when you have a numerical representation of a finite list (for example, departments in a company), and you want the user to choose them based on a friendly text name.
To bind the DropDownList to a model:
- Populate its
Dataparameter with the collection of items you want in the dropdown. - Set the
TextFieldandValueFieldparameters to point to the corresponding property names of the model. - Set the
Valueproperty to the initial value of the component (optional).
The
TextFieldandValueFieldparameters must point tostringor value type properties. TheValueparameter type must match the type of theValueFieldproperty.
Data binding a DropDownList to a model
<TelerikDropDownList Data="@DropDownListData"
@bind-Value="DropDownListValue"
TextField="@nameof(DropDownListItem.Text)"
ValueField="@nameof(DropDownListItem.Value)" />
@code {
private int DropDownListValue { get; set; }
private IEnumerable<DropDownListItem> DropDownListData = Enumerable.Range(1, 20)
.Select(x => new DropDownListItem { Text = $"Item {x}", Value = x });
protected override void OnInitialized()
{
DropDownListValue = 3;
}
public class DropDownListItem
{
public int Value { get; set; }
public string Text { get; set; } = string.Empty;
}
}
If you are looking for more fields from the view-model that describes the dropdown items, not just the
Value, see the Get model from dropdown KB article and the OnChange event.You may also want to review/join the discussion and Vote for this request: Binding DropDownList Value to complex model
Considerations
The DropDownList component attempts to infer the type of its model and value based on the provided Data and initial Value. This affects the way its reference is obtained and what happens if you can't provide data or a value. Providing a value that is not in the data source needs to be taken into account be the app, because the component will not change it.
Value Out of Range
When the Value the application provides does not match any of the values present in the ValueField of the Data collection, the DropDownList component will not change the Value or select a new item. In the common case, it will show up blank to indicate there is nothing selected from its data.
If you have set the DefaultText and the Value matches the default value of the type (for example, 0 for an int or null for an int? or string), you will see the DefaultText. A Value that is non-default will not show the DefaultText.
Handling such "unexpected" values is up to the application - for example, through defensive checks, or through form validation, or by first checking what is present in the data source before setting a new Value.
Component Reference
The DropDownList is a generic component and its type depends on the type of its Data and Value.
<TelerikDropDownList @ref="@DropDownListRef"
Data="@DropDownListData"
@bind-Value="DropDownListValue" />
@code {
private TelerikDropDownList<string, string>? DropDownListRef { get; set; }
private List<string> DropDownListData = new List<string>() { "first", "second", "third" };
private string DropDownListValue { get; set; } = string.Empty;
protected override void OnInitialized()
{
DropDownListValue = "second";
}
}
<TelerikDropDownList @ref="@DropDownListRef"
Data="@DropDownListData"
@bind-Value="DropDownListValue"
TextField="@nameof(DropDownListItem.Text)"
ValueField="@nameof(DropDownListItem.Value)" />
@code {
private TelerikDropDownList<DropDownListItem, int>? DropDownListRef { get; set; }
private int DropDownListValue { get; set; }
private IEnumerable<DropDownListItem> DropDownListData = Enumerable.Range(1, 20)
.Select(x => new DropDownListItem { Text = $"Item {x}", Value = x });
protected override void OnInitialized()
{
DropDownListValue = 3;
}
public class DropDownListItem
{
public int Value { get; set; }
public string Text { get; set; } = string.Empty;
}
}
Missing Value or Data
In case you cannot provide either of a Value, or Data, or both when the component initializes, you need to set the corresponding type properties to the TItem and TValue properties as shown below.
DropDownList configuration if you cannot provide Value or Data
<TelerikDropDownList Data="@DropDownListData"
TItem="@DropDownListItem"
TValue="@int"
TextField="@nameof(DropDownListItem.Text)"
ValueField="@nameof(DropDownListItem.Value)" />
@code {
private IEnumerable<DropDownListItem> DropDownListData = Enumerable.Range(1, 20)
.Select(x => new DropDownListItem { Text = $"Item {x}", Value = x });
public class DropDownListItem
{
public int Value { get; set; }
public string Text { get; set; } = string.Empty;
}
}