CODEWITHSUNDEEP
c#wpfdata-binding
Chris Chevalier
Chris Chevalier

Reputation: 196

Why is my SelectedValuePath property of my comboBox misbehaving?

I'm struggling to find why my SelectedValuePath isn't causing my combo box to pass a double to my view model property DelayLength. When I change the combo box selection during execution the combobox turns red and gives the error :

ConvertBack cannot convert value '[2 Seconds, 2]' (type 'KeyValuePair`2'). BindingExpression:Path=DelayLength; DataItem='TestViewModel' (HashCode=62605785); target element is 'ComboBox' (Name=''); target property is 'SelectedItem' (type 'Object') NotSupportedException:'System.NotSupportedException: DoubleConverter cannot convert from System.Collections.Generic.KeyValuePair`2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Double, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].

Is there something simple I'm missing because I believe I'm following documentation correctly?

Window.xaml 

    <ComboBox Width="120" Height="24" HorizontalAlignment="Left" Margin="5,0"
              DisplayMemberPath="Key"
              SelectedValuePath="Value"
              ItemsSource="{Binding AvailableLengths}"
              SelectedItem="{Binding DelayLength}"/>

    <TextBox Text="{Binding DelayLength, Mode=OneWay}" IsReadOnly="True"></TextBox>

</StackPanel>

Window.xaml.cs

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = new TestViewModel();
    }
}

TestViewModel.cs

class TestViewModel : GalaSoft.MvvmLight.ViewModelBase
{
    public Collection<KeyValuePair<string, double>> AvailableLengths
    {
        get
        {
            if (_availableLengths == null)
            {
                _availableLengths = new Collection<KeyValuePair<string, double>>()
                {
                    new KeyValuePair<string, double>("None", 0),
                    new KeyValuePair<string, double>("0.5 Seconds", 0.5),
                    new KeyValuePair<string, double>("1 Second", 1),
                    new KeyValuePair<string, double>("2 Seconds", 2),
                    new KeyValuePair<string, double>("3 Seconds", 3)
                };
            }

            return _availableLengths;
        }
    }

    private double _delayLength;

    public double DelayLength
    {
        get { return _delayLength; }
        set
        {
            _delayLength = value;
            RaisePropertyChanged(nameof(DelayLength));
        }
    }

    private Collection<KeyValuePair<string, double>> _availableLengths;
}

Upvotes: 3

Views: 1032

Answers (1)

Gaurang Dave
Gaurang Dave

Reputation: 4046

SelectedValuePath can not be used with SelectedItem. You have to use SelectedValue.

Customized summary from MSDN:

The SelectedValuePath property provides a way to specify a SelectedValue for the SelectedItem. The SelectedItem represents an object in the Items collection and Control displays the value of a single property of the selected item. The SelectedValuePath property specifies the path to the property that is used to determine the value of the SelectedValue property.

Upvotes: 3

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