Translating Binding from C# to XAML

Question

Hello,

i can't get this binding working in XAML.

Binding in c# works:

public partial class myControl : UserControl
{
    // get singleton instance
    InfoPool Info = InfoPool.Info;

    public myControl()
    {
        InitializeComponent();

        // Test Binding
        Binding bind = new Binding();
        bind.Source = this.Info;
        bind.Path = new PropertyPath("Time");
        txtInfoTime.SetBinding(TextBlock.TextProperty, bind);
    }
}

Binding in XAML not:

<TextBlock x:Name="txtInfoTime" Text="{Binding Path=Time, Source=Info}" />

Path and Source are the same, so where is my mistake?

Thx Rob

Answer 1

You can't translate it to XAML with the exact same properties, because there is no way to reference this.Info directly. However, you can achieve the same result by setting a RelativeSource :

<TextBlock x:Name="txtInfoTime" Text="{Binding Path=Info.Time, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type local:myControl}}}" />

Answer 2

You need to set the DataContext.

You can just add:

DataContext = Info

after

InitializeComponent();

And change XAML to:

<TextBlock x:Name="txtInfoTime" Text="{Binding Time}" />

Answer 3

You need to set the DataContext of your UserControl

1-Xaml

<Grid>
    <StackPanel Orientation="Horizontal">
        <TextBlock Text="Name">

        </TextBlock>
        <Separator Width="10" Opacity="0">

        </Separator>
        <TextBox Name="txtName" Width="100"  Text="{Binding Name}"></TextBox>
    </StackPanel>
</Grid>

2- Code

public partial class Window1 : Window { public Window1() { InitializeComponent();

        InfoPool info = new InfoPool();
        info.Name = "Saurabh";
        this.DataContext = info;

    }
}

public class InfoPool
{
    public string Name { get; set; }
}

Answer 4

Since InfoPool is a singleton instance i would recommend the following:

<TextBlock x:Name="txtInfoTime" Text="{Binding Path=Time, Source={x:Static ns:InfoPool.Info}}"/>

Where ns is the xaml-alias for the namespace in which InfoPool is defined. No need to mess up your DataContext this way.

Answer 5

Based on your answers I solved the Problem like described below. I post it, because i guess that other beginners in WPF could find it useful.

I have singleton class (InfoPool.cs) wich implements INotifyChangedProperty. It's used to provide appwide bindable properties. This class is used by an ObjectDataProvider in App.xaml. So it's very "easy" to bind to a property

InfoPool.cs (the Singleton code is from http://csharpindepth.com/Articles/General/Singleton.aspx 5th Version. I changed the Instance Property to GetInstance() Method, because the OPD needs an Method)

public sealed class InfoPool : INotifyPropertyChanged
{
    InfoPool()
    {
    }

    public static InfoPool GetInstance()
    {
        return Nested.instance;
    }

    class Nested
    {
        static Nested()
        {
        }

        internal static readonly InfoPool instance = new InfoPool();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, e);
        }
    }

    private String strProp = "default String";
    private Double dblProp = 1.23456;

    public String StrProp
    {
        get { return strProp; }
        set 
        { 
            strProp = value;
            OnPropertyChanged(new PropertyChangedEventArgs("StrProp"));
        }
    }

    public Double DblProp
    {
        get { return dblProp; }
        set 
        { 
            dblProp = value;
            OnPropertyChanged(new PropertyChangedEventArgs("DblProp"));
        }
    }

The ObjectDataProvider in App.xaml

<Application.Resources>
    <ResourceDictionary>
        <ObjectDataProvider x:Key="OPDInfo" ObjectType="{x:Type local:InfoPool}" MethodName="GetInstance" d:IsDataSource="True"/>
    </ResourceDictionary>
</Application.Resources>

An here are 2 ways to bind to the OPD

<StackPanel>
    <TextBlock x:Name="tbprop1" Text="{Binding Path=StrProp, Source={StaticResource OPDInfo}}" />
    <TextBlock x:Name="tbprop2" Text="{Binding DblProp}" ToolTip="{Binding StrProp}" DataContext="{StaticResource OPDInfo}" />
</StackPanel>

That's it. Please comment, cause I'm new to this ;-)

Answer 6

If you leave your singleton instance accessor as a property you don't need an ObjectDataProvider. You can just use the static instance directly.

<StackPanel>
<TextBlock x:Name="tbprop1" 
    Text="{Binding Path=StrProp, Source={x:Static local:InfoPool.Instance}}" /> 
</StackPanel>