Bind List<Object> to a comboxbox in c# wpf

Question

I have a static class named Building which contains a List<Beam> Beams as its property;

public static class Building
{
    public static readonly List<Beam> Beams = new List<Beam>();
}

public class Beam
{
    public string Story;
    public double Elevation;
}

I'm trying to Bind the Building.Beams to a combobox in XAML so that Elevation and Story properties of each item in Building.Beams list is displayed in different columns in the combobox. I have been able to implement the two columns, I just can't Bind these properties.

Here is what I have tried so far:

<ComboBox x:Name="cmbBuilding"  ItemsSource="{Binding}">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <Grid Width="300">
                <TextBlock Width="150"  Text="{Binding Path=Story }"/>
                <TextBlock Width="150" Text="{Binding Path=Elevation}"/>
            </Grid>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

var b1 = new Beam { Elevation = 320, Story = "ST1" };
var b2 = new Beam { Elevation = 640, Story = "ST2" };
Building.Beams.Add(b1);
Building.Beams.Add(b2);

Rohit Vats · Accepted Answer · 2014-04-06 20:26:13Z

2

First of all you can't bind with fields.

Convert Story and Elevation to properties (automatic properties in your case will do)

public class Beam
{
    public string Story { get; set;}
    public double Elevation { get; set;}
}

Second, you should use ObservableCollection in case you are adding items to the list after loading finishes so that UI gets notification.

public static readonly ObservableCollection<Beam> Beams
                                   = new ObservableCollection<Beam>();

answered Apr 6, 2014 at 20:26

Rohit Vats

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1 Comment

Vahid Over a year ago

Wow. Thank you. I've been working on this for nearly 3 hours now!

Anatoliy Nikolaev · Accepted Answer · 2014-04-06 20:35:33Z

1

Try this example:

XAML

<Grid>
    <ComboBox x:Name="cmbBuilding" Width="100" Height="25" ItemsSource="{Binding Path=Beams}">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <Grid Width="300">
                    <TextBlock Width="150" Text="{Binding Path=Story}" HorizontalAlignment="Left" />
                    <TextBlock Width="150" Text="{Binding Path=Elevation}" HorizontalAlignment="Right" />
                </Grid>
            </DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>

    <Button Content="Add item" VerticalAlignment="Top" Click="Button_Click" />
</Grid>

Code-behind

public partial class MainWindow : Window
{
    Building building = new Building();

    public MainWindow()
    {
        InitializeComponent();

        building.Beams = new List<Beam>();

        building.Beams.Add(new Beam 
                           { 
                               Elevation = 320, 
                               Story = "ST1" 
                           });

        this.DataContext = building;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        var b1 = new Beam { Elevation = 320, Story = "ST1" };
        var b2 = new Beam { Elevation = 640, Story = "ST2" };

        building.Beams.Add(b1);
        building.Beams.Add(b2);

        cmbBuilding.Items.Refresh();
    }
}

public class Building
{
    public List<Beam> Beams
    {
        get;
        set;
    }
}

public class Beam
{
    public string Story 
    {
        get;
        set;
    }

    public double Elevation
    {
        get;
        set;
    }
}

Some notes

When you use properties in the Binding, you need to be properties with get and set, not fields.
Properties, what were added to the List<T> will automatically update, you should call MyComboBox.Items.Refresh() method, or use ObservableCollection<T>:

ObservableCollection represents a dynamic data collection that provides notifications when items get added, removed, or when the whole list is refreshed.

edited Apr 6, 2014 at 20:35

answered Apr 6, 2014 at 20:29

Anatoliy Nikolaev

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10 Comments

Vahid Over a year ago

Thank you so much Anatoliy for the time you put into this. I'm always learning from guys like you.

Vahid Over a year ago

Just one thing, my Building class is static. So it wouldn't let me to assign it as a DataContext. So I had to do this: DataContext = Building.Beams Is there a better way?

Anatoliy Nikolaev Over a year ago

@Vahid: Why do you use static here? Binding usually not used static classes, I advise to do as my example. For Binding in static class, implementing pattern Singleton.

Vahid Over a year ago

I've heard that Singleton pattern must be used in very rare situations. Actually I have built my whole program around this static Building class so I have to stick to it.

Anatoliy Nikolaev Over a year ago

I've heard that Singleton pattern must be used in very rare situations. - I think this is your case. Or are you doing in my example, or to implement a Singleton pattern. You can create a new question about this problem, if you want.

|

TDaddy Hobz · Accepted Answer · 2014-04-06 20:27:32Z

1

Is it maybe because you have declared Beams as readonly yet you try to ADD items to it? Beams is also defined as a variable, try removing the readonly and making it a property with a getter and setter

answered Apr 6, 2014 at 20:27

TDaddy Hobz

4644 silver badges11 bronze badges

1 Comment

Vahid Over a year ago

Yes, it was because of the fields I had used instead of the properties. Thanks

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