MVVM: Binding radio buttons to a view model?

Question

EDIT: Problem was fixed in .NET 4.0.

I have been trying to bind a group of radio buttons to a view model using the IsChecked button. After reviewing other posts, it appears that the IsChecked property simply doesn't work. I have put together a short demo that reproduces the problem, which I have included below.

Here is my question: Is there a straightforward and reliable way to bind radio buttons using MVVM? Thanks.

Additional information: The IsChecked property doesn't work for two reasons:

1. When a button is selected, the IsChecked properties of other buttons in the group don't get set to false.

2. When a button is selected, its own IsChecked property does not get set after the first time the button is selected. I am guessing that the binding is getting trashed by WPF on the first click.

Demo project: Here is the code and markup for a simple demo that reproduces the problem. Create a WPF project and replace the markup in Window1.xaml with the following:

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
    <StackPanel>
        <RadioButton Content="Button A" IsChecked="{Binding Path=ButtonAIsChecked, Mode=TwoWay}" />
        <RadioButton Content="Button B" IsChecked="{Binding Path=ButtonBIsChecked, Mode=TwoWay}" />
    </StackPanel>
</Window>

Replace the code in Window1.xaml.cs with the following code (a hack), which sets the view model:

using System.Windows;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            this.DataContext = new Window1ViewModel();
        }
    }
}

Now add the following code to the project as Window1ViewModel.cs:

using System.Windows;

namespace WpfApplication1
{
    public class Window1ViewModel
    {
        private bool p_ButtonAIsChecked;

        /// <summary>
        /// Summary
        /// </summary>
        public bool ButtonAIsChecked
        {
            get { return p_ButtonAIsChecked; }
            set
            {
                p_ButtonAIsChecked = value;
                MessageBox.Show(string.Format("Button A is checked: {0}", value));
            }
        }

        private bool p_ButtonBIsChecked;

        /// <summary>
        /// Summary
        /// </summary>
        public bool ButtonBIsChecked
        {
            get { return p_ButtonBIsChecked; }
            set
            {
                p_ButtonBIsChecked = value;
                MessageBox.Show(string.Format("Button B is checked: {0}", value));
            }
        }

    }
}

To reproduce the problem, run the app and click Button A. A message box will appear, saying that Button A's IsChecked property has been set to true. Now select Button B. Another message box will appear, saying that Button B's IsChecked property has been set to true, but there is no message box indicating that Button A's IsChecked property has been set to false--the property hasn't been changed.

Now click Button A again. The button will be selected in the window, but no message box will appear--the IsChecked property has not been changed. Finally, click on Button B again--same result. The IsChecked property is not updated at all for either button after the button is first clicked.

Vas

+1 just for the fact that you posted all the code to reproduce it. – Captainship

This is a duplicate question to: https://mcmap.net/q/281375/-mvvm-radiobuttons – Instal

Can you put a thick bold remark on top of your question that your problem is only a problem with target framework 3.5. The issue has been fixed in .NET 4.0 and your demo project runs as expected in .NET 4. I've just tested your demo project on both platforms and your problem is only reproducable in .NET 3.5 (see also RandomEngy's answer below who confirms this). – Bifoliate

Answer 1

If you start with Jason's suggestion then the problem becomes a single bound selection from a list which translates very nicely to a ListBox. At that point it's trivial to apply styling to a ListBox control so that it shows up as a RadioButton list.

<ListBox ItemsSource="{Binding ...}" SelectedItem="{Binding ...}">
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ListBoxItem}">
                        <RadioButton Content="{TemplateBinding Content}"
                                     IsChecked="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=IsSelected}"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

Selectee

List box is the best solution of those proposed. But see https://mcmap.net/q/281375/-mvvm-radiobuttons for another solution. – Vas

Jaime Rodriguez has a very simple solution to the problem--set each RadioButton's GroupName to a different value. Putting each button in a different group keeps the bindings from getting wiped out when a button is selected. See the thread I referred to in my previous comment. In my app, the list box solution works best, so it is the selected answer. – Vas

Yeah, there are so many different approaches to this that can work. I also used to use a method that relied on a converter which would return Binding.DoNothing for unchecked buttons to avoid breaking the bindings but ended up using this more often because it's less code. Good conversation starter! – Selectee

When I first realized my problem I was concerned, but this post made it all better. – Retiarius

DisplayMember seems to have no effect, it shows object. – Linsk

@Linsk See my answer for that, which should address this problem. – Noenoel

Answer 2

Looks like they fixed binding to the IsChecked property in .NET 4. A project that was broken in VS2008 works in VS2010.

Bluepencil

Confirmed! The demo project in the question works in .NET 4 as expected. – Bifoliate

I can confirm this too! – Incursion

Answer 3

For the benefit of anyone researching this question down the road, here is the solution I ultimately implemented. It builds on John Bowen's answer, which I selected as the best solution to the problem.

First, I created a style for a transparent list box containing radio buttons as items. Then, I created the buttons to go in the list box--my buttons are fixed, rather than read into the app as data, so I hard-coded them into the markup.

I use an enum called ListButtons in the view model to represent the buttons in the list box, and I use each button's Tag property to pass a string value of the enum value to use for that button. The ListBox.SelectedValuePath property allows me to specify the Tag property as the source for the selected value, which I bind to the view model using the SelectedValue property. I thought I would need a value converter to convert between the string and its enum value, but WPF's built-in converters handled the conversion without problem.

Here is the complete markup for Window1.xaml:

<Window x:Class="RadioButtonMvvmDemo.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">

    <!-- Resources -->
    <Window.Resources>
        <Style x:Key="RadioButtonList" TargetType="{x:Type ListBox}">
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="ItemContainerStyle">
                <Setter.Value>
                    <Style TargetType="{x:Type ListBoxItem}" >
                        <Setter Property="Margin" Value="5" />
                        <Setter Property="Template">
                            <Setter.Value>
                                <ControlTemplate TargetType="{x:Type ListBoxItem}">
                                    <Border BorderThickness="0" Background="Transparent">
                                        <RadioButton 
                                            Focusable="False"
                                            IsHitTestVisible="False"
                                            IsChecked="{TemplateBinding IsSelected}">
                                            <ContentPresenter />
                                        </RadioButton>
                                    </Border>
                                </ControlTemplate>
                            </Setter.Value>
                        </Setter>
                    </Style>
                </Setter.Value>
            </Setter>
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ListBox}">
                        <Border BorderThickness="0" Padding="0" BorderBrush="Transparent" Background="Transparent" Name="Bd" SnapsToDevicePixels="True">
                            <ItemsPresenter SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>

    <!-- Layout -->
    <Grid>
        <!-- Note that we use SelectedValue, instead of SelectedItem. This allows us 
        to specify the property to take the value from, using SelectedValuePath. -->

        <ListBox Style="{StaticResource RadioButtonList}" SelectedValuePath="Tag" SelectedValue="{Binding Path=SelectedButton}">
            <ListBoxItem Tag="ButtonA">Button A</ListBoxItem>
            <ListBoxItem Tag="ButtonB">Button B</ListBoxItem>
        </ListBox>
    </Grid>
</Window>

The view model has a single property, SelectedButton, which uses a ListButtons enum to show which button is selected. The property calls an event in the base class I use for view models, which raises the PropertyChanged event:

namespace RadioButtonMvvmDemo
{
    public enum ListButtons {ButtonA, ButtonB}

    public class Window1ViewModel : ViewModelBase
    {
        private ListButtons p_SelectedButton;

        public Window1ViewModel()
        {
            SelectedButton = ListButtons.ButtonB;
        }

        /// <summary>
        /// The button selected by the user.
        /// </summary>
        public ListButtons SelectedButton
        {
            get { return p_SelectedButton; }

            set
            {
                p_SelectedButton = value;
                base.RaisePropertyChangedEvent("SelectedButton");
            }
        }

    }
} 

In my production app, the SelectedButton setter will call a service class method that will take the action required when a button is selected.

And to be complete, here is the base class:

using System.ComponentModel;

namespace RadioButtonMvvmDemo
{
    public abstract class ViewModelBase : INotifyPropertyChanged
    {
        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion

        #region Protected Methods

        /// <summary>
        /// Raises the PropertyChanged event.
        /// </summary>
        /// <param name="propertyName">The name of the changed property.</param>
        protected void RaisePropertyChangedEvent(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChangedEventArgs e = new PropertyChangedEventArgs(propertyName);
                PropertyChanged(this, e);
            }
        }

        #endregion
    }
}

Hope that helps!

Vas

Answer 4

One solution is to update the ViewModel for the radio buttons in the setter of the properties. When Button A is set to True, set Button B to false.

Another important factor when binding to an object in the DataContext is that the object should implement INotifyPropertyChanged. When any bound property changes, the event should be fired and include the name of the changed property. (Null check omitted in the sample for brevity.)

public class ViewModel  : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected bool _ButtonAChecked = true;
    public bool ButtonAChecked
    {
        get { return _ButtonAChecked; }
        set 
        { 
            _ButtonAChecked = value;
            PropertyChanged(this, new PropertyChangedEventArgs("ButtonAChecked"));
            if (value) ButtonBChecked = false;
        }
    }

    protected bool _ButtonBChecked;
    public bool ButtonBChecked
    {
        get { return _ButtonBChecked; }
        set 
        { 
            _ButtonBChecked = value; 
            PropertyChanged(this, new PropertyChangedEventArgs("ButtonBChecked"));
            if (value) ButtonAChecked = false;
        }
    }
}

Edit:

The issue is that when first clicking on Button B the IsChecked value changes and the binding feeds through, but Button A does not feed through its unchecked state to the ButtonAChecked property. By manually updating in code the ButtonAChecked property setter will get called the next time Button A is clicked.

Breadth

I don't think this proposed solution addresses the issue of the bindings getting trashed when a button is selected. – Vas

When I tested it with breakpoints on the setters, the setters would get hit each time I toggled back and forth between the two radio buttons. It would seem that the bindings do not get destroyed. – Breadth

Answer 5

Here is another way you can do it

VIEW:

<StackPanel Margin="90,328,965,389" Orientation="Horizontal">
        <RadioButton Content="Mr" Command="{Binding TitleCommand, Mode=TwoWay}" CommandParameter="{Binding Content, RelativeSource={RelativeSource Mode=Self}, Mode=TwoWay}" GroupName="Title"/>
        <RadioButton Content="Mrs" Command="{Binding TitleCommand, Mode=TwoWay}" CommandParameter="{Binding Content, RelativeSource={RelativeSource Mode=Self}, Mode=TwoWay}" GroupName="Title"/>
        <RadioButton Content="Ms" Command="{Binding TitleCommand, Mode=TwoWay}" CommandParameter="{Binding Content, RelativeSource={RelativeSource Mode=Self}, Mode=TwoWay}" GroupName="Title"/>
        <RadioButton Content="Other" Command="{Binding TitleCommand, Mode=TwoWay}" CommandParameter="{Binding Content, RelativeSource={RelativeSource Mode=Self}}" GroupName="Title"/>
        <TextBlock Text="{Binding SelectedTitle, Mode=TwoWay}"/>
    </StackPanel>

ViewModel:

 private string selectedTitle;
    public string SelectedTitle
    {
        get { return selectedTitle; }
        set
        {
            SetProperty(ref selectedTitle, value);
        }
    }

    public RelayCommand TitleCommand
    {
        get
        {
            return new RelayCommand((p) =>
            {
                selectedTitle = (string)p;
            });
        }
    }

Mislike

This works well for binding the text of a TextBlock, but doesn't help with binding the IsChecked property of the RadioButton. – Winfredwinfrey

Answer 6

Not sure about any IsChecked bugs, one possible refactor you could make to your viewmodel:the view has a number of mutually exclusive states represented by a series of RadioButtons, only one of which at any given time can be selected. In the view model, just have 1 property (e.g. an enum) which represents the possible states: stateA, stateB, etc That way you wouldn't need all the individual ButtonAIsChecked, etc

Chuvash

Thanks, but that doesn't really address the question. Even with that refactoring, you still have the problem of failure on the second click of a button. – Vas

Answer 7

A small extension to John Bowen's answer: It doesn't work when the values don't implement ToString(). What you need instead of setting the Content of the RadioButton to a TemplateBinding, just put a ContentPresenter in it, like this:

<ListBox ItemsSource="{Binding ...}" SelectedItem="{Binding ...}">
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ListBoxItem}">
                        <RadioButton IsChecked="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=IsSelected}">
                            <ContentPresenter/>
                        </RadioButton>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

This way you can additionally use DisplayMemberPath or an ItemTemplate as appropriate. The RadioButton just "wraps" the items, providing the selection.

Synthiasyntonic

Answer 8

I know this is an old question and the original issue was resolved in .NET 4. and in all honesty this is slightly off topic.

In most cases where I've wanted to use RadioButtons in MVVM it's to select between elements of an enum, this requires binding a bool property in the VM space to each button and using them to set an overall enum property that reflects the actual selection, this gets very tedious very quick. So I came up with a solution that is re-usable and very easy to implement, and does not require ValueConverters.

The View is pretty much the same, but once you have your enum in place the VM side can be done with a single property.

MainWindowVM

using System.ComponentModel;

namespace EnumSelectorTest
{
  public class MainWindowVM : INotifyPropertyChanged
  {
    public EnumSelectorVM Selector { get; set; }

    private string _colorName;
    public string ColorName
    {
      get { return _colorName; }
      set
      {
        if (_colorName == value) return;
        _colorName = value;
        RaisePropertyChanged("ColorName");
      }
    }

    public MainWindowVM()
    {
      Selector = new EnumSelectorVM
        (
          typeof(MyColors),
          MyColors.Red,
          false,
          val => ColorName = "The color is " + ((MyColors)val).ToString()
        );
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void RaisePropertyChanged(string propertyName)
    {
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
  }
}

The class that does all the work inherits from DynamicObject. Viewed from the outside it creates a bool property for each element in the enum prefixed with 'Is', 'IsRed', 'IsBlue' etc. that can be bound to from XAML. Along with a Value property that holds the actual enum value.

public enum MyColors
{
  Red,
  Magenta,
  Green,
  Cyan,
  Blue,
  Yellow
}

EnumSelectorVM

using System;
using System.ComponentModel;
using System.Dynamic;
using System.Linq;

namespace EnumSelectorTest
{
  public class EnumSelectorVM : DynamicObject, INotifyPropertyChanged
  {
    //------------------------------------------------------------------------------------------------------------------------------------------
    #region Fields

    private readonly Action<object> _action;
    private readonly Type _enumType;
    private readonly string[] _enumNames;
    private readonly bool _notifyAll;

    #endregion Fields

    //------------------------------------------------------------------------------------------------------------------------------------------
    #region Properties

    private object _value;
    public object Value
    {
      get { return _value; }
      set
      {
        if (_value == value) return;
        _value = value;
        RaisePropertyChanged("Value");
        _action?.Invoke(_value);
      }
    }

    #endregion Properties

    //------------------------------------------------------------------------------------------------------------------------------------------
    #region Constructor

    public EnumSelectorVM(Type enumType, object initialValue, bool notifyAll = false, Action<object> action = null)
    {
      if (!enumType.IsEnum)
        throw new ArgumentException("enumType must be of Type: Enum");
      _enumType = enumType;
      _enumNames = enumType.GetEnumNames();
      _notifyAll = notifyAll;
      _action = action;

      //do last so notification fires and action is executed
      Value = initialValue;
    }

    #endregion Constructor

    //------------------------------------------------------------------------------------------------------------------------------------------
    #region Methods

    //---------------------------------------------------------------------
    #region Public Methods

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
      string elementName;
      if (!TryGetEnumElemntName(binder.Name, out elementName))
      {
        result = null;
        return false;
      }
      try
      {
        result = Value.Equals(Enum.Parse(_enumType, elementName));
      }
      catch (Exception ex) when (ex is ArgumentNullException || ex is ArgumentException || ex is OverflowException)
      {
        result = null;
        return false;
      }
      return true;
    }

    public override bool TrySetMember(SetMemberBinder binder, object newValue)
    {
      if (!(newValue is bool))
        return false;
      string elementName;
      if (!TryGetEnumElemntName(binder.Name, out elementName))
        return false;
      try
      {
        if((bool) newValue)
          Value = Enum.Parse(_enumType, elementName);
      }
      catch (Exception ex) when (ex is ArgumentNullException || ex is ArgumentException || ex is OverflowException)
      {
        return false;
      }
      if (_notifyAll)
        foreach (var name in _enumNames)
          RaisePropertyChanged("Is" + name);
      else
        RaisePropertyChanged("Is" + elementName);
      return true;
    }

    #endregion Public Methods

    //---------------------------------------------------------------------
    #region Private Methods

    private bool TryGetEnumElemntName(string bindingName, out string elementName)
    {
      elementName = "";
      if (bindingName.IndexOf("Is", StringComparison.Ordinal) != 0)
        return false;
      var name = bindingName.Remove(0, 2); // remove first 2 chars "Is"
      if (!_enumNames.Contains(name))
        return false;
      elementName = name;
      return true;
    }

    #endregion Private Methods

    #endregion Methods

    //------------------------------------------------------------------------------------------------------------------------------------------
    #region Events

    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void RaisePropertyChanged(string propertyName)
    {
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion Events
  }
}

To respond to changes you can either subscribe to the NotifyPropertyChanged event or pass an anonymous method to the constructor as done above.

And finally the MainWindow.xaml

<Window x:Class="EnumSelectorTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525">  
  <Grid>
    <StackPanel>
      <RadioButton IsChecked="{Binding Selector.IsRed}">Red</RadioButton>
      <RadioButton IsChecked="{Binding Selector.IsMagenta}">Magenta</RadioButton>
      <RadioButton IsChecked="{Binding Selector.IsBlue}">Blue</RadioButton>
      <RadioButton IsChecked="{Binding Selector.IsCyan}">Cyan</RadioButton>
      <RadioButton IsChecked="{Binding Selector.IsGreen}">Green</RadioButton>
      <RadioButton IsChecked="{Binding Selector.IsYellow}">Yellow</RadioButton>
      <TextBlock Text="{Binding ColorName}"/>
    </StackPanel>
  </Grid>
</Window>

Hope someone else finds this useful, 'cause I reckon this ones going in my toolbox.

Walther

Answer 9

You have to add the Group Name for the Radio button

   <StackPanel>
        <RadioButton Content="Button A" IsChecked="{Binding Path=ButtonAIsChecked, Mode=TwoWay}" GroupName="groupName" />
        <RadioButton Content="Button B" IsChecked="{Binding Path=ButtonBIsChecked, Mode=TwoWay}" GroupName="groupName" />
    </StackPanel>

Upon

Answer 10

I have a very similar problem in VS2015 and .NET 4.5.1

XAML:

                <ListView.ItemsPanel>
                    <ItemsPanelTemplate>
                        <UniformGrid Columns="6" Rows="1"/>
                    </ItemsPanelTemplate>
                </ListView.ItemsPanel>
                <ListView.ItemTemplate>
                    <DataTemplate >
                        <RadioButton  GroupName="callGroup" Style="{StaticResource itemListViewToggle}" Click="calls_ItemClick" Margin="1" IsChecked="{Binding Path=Selected,Mode=TwoWay}" Unchecked="callGroup_Checked"  Checked="callGroup_Checked">

....

As you can see in this code i have a listview, and items in template are radiobuttons that belongs to a groupname.

If I add a new item to the collection with the property Selected set to True it appears checked and the rest of buttons remain checked.

I solve it by getting the checkedbutton first and set it to false manually but this is not the way it's supposed to be done.

code behind:

`....
  lstInCallList.ItemsSource = ContactCallList
  AddHandler ContactCallList.CollectionChanged, AddressOf collectionInCall_change
.....
Public Sub collectionInCall_change(sender As Object, e As NotifyCollectionChangedEventArgs)
    'Whenever collection change we must test if there is no selection and autoselect first.   
    If e.Action = NotifyCollectionChangedAction.Add Then
        'The solution is this, but this shouldn't be necessary
        'Dim seleccionado As RadioButton = getCheckedRB(lstInCallList)
        'If seleccionado IsNot Nothing Then
        '    seleccionado.IsChecked = False
        'End If
        DirectCast(e.NewItems(0), PhoneCall).Selected = True
.....
End sub

`

Devon

Answer 11

<RadioButton  IsChecked="{Binding customer.isMaleFemale}">Male</RadioButton>
    <RadioButton IsChecked="{Binding customer.isMaleFemale,Converter=      {StaticResource GenderConvertor}}">Female</RadioButton>

Below is the code for IValueConverter

public class GenderConvertor : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return !(bool)value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return !(bool)value;
    }
}

this worked for me. Even value got binded on both view and viewmodel according to the radio button click. True--> Male and False-->Female

Barrens