Determining checked Radiobutton from groupbox in WPF following MVVM

Question

I have a groupbox with some radiobuttons. How do I get to know which one which is checked? I am using WPF and following MVVM.

<GroupBox Name="grpbx_pagerange" Header="Print Range">
    <Grid >
        <RadioButton Name="radbtn_all" Content="All Pages" GroupName="radios_page_range" IsChecked="True"  />
        <RadioButton x:Name="radbtn_curr" Content="Current Page" GroupName="radios_page_range"  />
        <RadioButton Name="radbtn_pages" Content="Page Range" GroupName="radios_page_range" />

        ....

</GroupBox>

Now, one way I could figure out was to bind each RadioButton's IsChecked Property to some property in ViewModel and then do if..else sort of logic in my ViewModel to figure out the selected radiobutton.

But Is there any other elegant way?

Answer 1

you can bind RadioButton.Command of Radiobuttons to a command of your ViewModel and send a unique CommandParameter to identify which button has called the command in commandhandler.

<RadioButton Command="{Binding MyCommand}" CommandParameter="Radio1"/>
<RadioButton Command="{Binding MyCommand}" CommandParameter="Radio2"/>
<RadioButton Command="{Binding MyCommand}" CommandParameter="Radio3"/>

in command handler check for parameter to identify the radiobutton.

Thanks

Answer 2

You can create an enum that contains the values of the RadioButton objects as names (roughly) and then bind the IsChecked property to a property of the type of this enum using an EnumToBoolConverter.

public enum Options
{
    All, Current, Range
}

Then in your view model or code behind:

private Options options = Options.All; // set your default value here

public Options Options
{ 
    get { return options; }
    set { options = value; NotifyPropertyChanged("Options"); }
}

Add the Converter:

[ValueConversion(typeof(Enum), typeof(bool))]
public class EnumToBoolConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null || parameter == null) return false;
        string enumValue = value.ToString();
        string targetValue = parameter.ToString();
        bool outputValue = enumValue.Equals(targetValue, StringComparison.InvariantCultureIgnoreCase);
        return outputValue;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null || parameter == null) return null;
        bool useValue = (bool)value;
        string targetValue = parameter.ToString();
        if (useValue) return Enum.Parse(targetType, targetValue);
        return null;
    }
}

Then finally, add the bindings in the UI, setting the appropriate ConverterParameter:

<RadioButton Content="All Pages" IsChecked="{Binding Options, Converter={
    StaticResource EnumToBoolConverter}, ConverterParameter=All}" />
<RadioButton Content="Current Page" IsChecked="{Binding Options, Converter={
    StaticResource EnumToBoolConverter}, ConverterParameter=Current}" />
<RadioButton Content="Page Range" IsChecked="{Binding Options, Converter={
    StaticResource EnumToBoolConverter}, ConverterParameter=Range}" />

Now you can tell which is set by looking at the Options variable in your view model or code behind. You'll also be able to set the checked RadioButton by setting the Options property.

Answer 3

There is another MVVM way to solve this using IsChecked Property

Here's the XAML

<Page>
<Page.Resources>
<DataTemplate x:Key="ChoiceItemTemplate">
<RadioButton Content="{Binding individualRadioButtonText}"
     IsTabStop="True"
     GroupName="choice"
     IsChecked="{Binding IsChecked, Mode=TwoWay}"/>
 </DataTemplate>
</Page.Resources>


 <StackPanel>
  <TextBlock Text="{Binding ChoiceQuestion}" />
 <ItemsControl  ItemsSource="{Binding ListOfAnswerOptions}"
                ItemTemplate="{StaticResource ChoiceItemTemplate}" />
 </StackPanel>
</Page>

Your model will be something like this

 public class RadioButtonQuestion
 {
    public string ChoiceQuestion { get; set; }
    public string answer { get; set; }
    public List<AnswerOption> ListOfAnswerOptions { get; set; }
 }

 public class AnswerOption
 {
    public string individualRadioButtonText { get; set; }
    public bool IsChecked { get; set; }
 }

ViewModel will look something like this (The selection logic)

RadioButtonQuestion r = new RadioButtonQuestion();
var selectedElement = rbuttonQuestion.answerOptions.FirstOrDefault(c => c.IsChecked);
r.answer = selectedElement.individualRadioButtonText;

So if you set the datacontext of the view to this viewmodel. You must be able to get it to work.

Hope it helps.

Answer 4

If you use Tag property on options buttons (boolean, integer, strings) like in his XAML

<StackPanel Orientation="Horizontal" Margin="10,10, 0, 0">
    <RadioButton Name="rP0" Content="Low  " Tag="0" />
    <RadioButton Name="rP1" Content="Normal" Tag="1" IsChecked="True" />
    <RadioButton Name="rP2" Content="Medium" Tag="2" />
    <RadioButton Name="rP3" Content="High" Tag="3" />
</StackPanel>

Then you can use following function to get selected value (button)

int priority = SelectedRadioValue<int>(0, rP0, rP1, rP2, rP3);

where

public T SelectedRadioValue<T>(T defaultValue, params RadioButton[] buttons)
{
    foreach (RadioButton button in buttons)
    {
        if (button.IsChecked == true)
        {
            if (button.Tag is string && typeof(T) != typeof(string))
            {
                string value = (string) button.Tag;
                return (T) Convert.ChangeType(value, typeof(T));
            }

            return (T)button.Tag;
        }
    }

    return defaultValue;
}