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RadioGroup Data Binding

This article explains the different ways to provide data to a RadioGroup 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:

and some considerations you may find useful, such as handling values not in the list, or when the value is out of the data source range:

Primitive Types

You can data bind the RadioGroup to a simple collection of data. 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.

To bind the RadioGroup to a primitive type (like int, string, double), you need to

  1. Provide an IEnumerable<TItem> of the desired type to its Data property
  2. Set a corresponding Value.

Data binding a RadioGroup to a primitive type

@SelectedValue
<br />
<TelerikRadioGroup Data="@Data" @bind-Value="@SelectedValue"></TelerikRadioGroup>
@code{
    string SelectedValue { get; set; }
    IEnumerable<string> Data { get; set; } = new List<string> { "first", "second", "third" };
}

Bind to a Model

You can bind the RadioGroup 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 RadioGroup to a model:

  1. Populate its Data property with the collection of items you want in the list.
  2. Set the TextField and ValueField properties to point to the corresponding names of the model.
  3. Bind the Value parameter to the desired field of the view-model. It is populated from the ValueField so it must match the its type.

Data binding a RadioGroup to a model and collection of models

Chosen gender: @( ChosenGender == 0 ? "no selection yet" : ChosenGender.ToString() )
<br />

<TelerikRadioGroup Data="@GenderOptions"
                   @bind-Value="@ChosenGender"
                   ValueField="@nameof(GenderModel.GenderId)"
                   TextField="@nameof(GenderModel.GenderText)">
</TelerikRadioGroup>

@code{
    int ChosenGender { get; set; }

    List<GenderModel> GenderOptions { get; set; } = new List<GenderModel>
    {
        new GenderModel { GenderId = 1, GenderText = "Female" },
        new GenderModel { GenderId = 2, GenderText = "Male" },
        new GenderModel { GenderId = 3, GenderText = "Other" },
        new GenderModel { GenderId = 4, GenderText = "Prefer not to say" },
    };

    public class GenderModel
    {
        public int GenderId { get; set; }
        public string GenderText { get; set; }
    }
}

Considerations

The RadioGroup 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 by 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 RadioGroup 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.

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.

The RadioGroup component will not select an item by default if the initial value of the Value field in the view-model does not match any of the values in its data source.

You should avoide values in the data that match the default of their type (such as 0 for an int) because that can result in an item being selected by default even if you do not intend that, or in validation passing without the user choosing a correct option.

Component Reference

The RadioGroup is a generic component and its type comes from the model it is bound to and from the value field type. When bound to a primitive type, the reference is of that primitive type only.

Reference type when binding to primitive values

<TelerikRadioGroup Data="@Data" @bind-Value="@SelectedValue" @ref="@RadioGroupRef"></TelerikRadioGroup>
@code{
    TelerikRadioGroup<string, string> RadioGroupRef { get; set; }

    string SelectedValue { get; set; }
    IEnumerable<string> Data { get; set; } = new List<string> { "first", "second", "third" };
}

Reference when binding to model collections

<TelerikRadioGroup Data="@GenderOptions"
                   @bind-Value="@ChosenGender"
                   @ref="@RadioGroupRef"
                   ValueField="@nameof(GenderModel.GenderId)"
                   TextField="@nameof(GenderModel.GenderText)">
</TelerikRadioGroup>

@code{
    TelerikRadioGroup<GenderModel, int> RadioGroupRef { get; set; }

    int ChosenGender { get; set; }

    List<GenderModel> GenderOptions { get; set; } = new List<GenderModel>
    {
        new GenderModel { GenderId = 1, GenderText = "Female" },
        new GenderModel { GenderId = 2, GenderText = "Male" },
        new GenderModel { GenderId = 3, GenderText = "Other" },
        new GenderModel { GenderId = 4, GenderText = "Prefer not to say" },
    };

    public class GenderModel
    {
        public int GenderId { get; set; }
        public string GenderText { get; set; }
    }
}

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.

RadioGroup configuration if you cannot provide Value or Data

How to declare the radio button list if no Value or Data are provided

<TelerikRadioGroup Data="@GenderOptions"
                   TItem="GenderModel" TValue="int"
                   ValueField="@nameof(GenderModel.GenderId)"
                   TextField="@nameof(GenderModel.GenderText)">
</TelerikRadioGroup>

@code{
    TelerikRadioGroup<GenderModel, int> RadioGroupRef { get; set; }

    int ChosenGender { get; set; }

    List<GenderModel> GenderOptions { get; set; } = new List<GenderModel>
    {
        new GenderModel { GenderId = 1, GenderText = "Female" },
        new GenderModel { GenderId = 2, GenderText = "Male" },
        new GenderModel { GenderId = 3, GenderText = "Other" },
        new GenderModel { GenderId = 4, GenderText = "Prefer not to say" },
    };

    public class GenderModel //TItem matches the type of the model
    {
        public int GenderId { get; set; } //TValue matches the type of the value field
        public string GenderText { get; set; }
    }

    //the same configuration applies if the "myDdlData" object is null initially and is populated on some event
}

See Also

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