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Dependency Property is not updating my Usercontrol

The line below works for the TextBox DP Text, where CellNo is a property of a class which derives from INotifyPropertychanged. So here when I change the CellNo the Text will be updated and When I change the CellNo the Text will be updated. This will work fine.

Text="{Binding Path = CellNo, Mode=TwoWay,  UpdateSourceTrigger=PropertyChanged}"

I have create a user control which contain only one TextBox. I have defined one DP name CellValue as below:

public string CellValue
    {
        get { return (string)GetValue(CellValueProperty); }
        set { SetValue(CellValueProperty, value); }
    }

    // Using a DependencyProperty as the backing store for LimitValue.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty CellValueProperty =
        DependencyProperty.Register("CellValue", typeof(string), typeof(control), new FrameworkPropertyMetadata
        {
            BindsTwoWayByDefault = true,
        });

Now when I use this user control in any dialog and do the same binding as above, the Target ( TextBox inside User control) is NOT updating.

 <local:control
        x:Name="control" 
        CellValue="{Binding Path = CellNo, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">

Also inside user control I have binded the Text Property of TextBox to CellValue DP.

Inside User control

<TextBox                 
        Text="{Binding Path = CellValue}"
        Name="textBox2" />

I want when the CellValue changes the TextBox Text should also be updated, but with the above appoach it remains blank.

like image 346
Ashish Ashu Avatar asked Nov 15 '10 07:11

Ashish Ashu


1 Answers

This code

<local:control x:Name="control"  
               CellValue="{Binding Path=CellNo,
                                   Mode=TwoWay,
                                   UpdateSourceTrigger=PropertyChanged}">

is trying to bind against the Property CellNo of the UserControl. Add RelativeSource or ElementName and it'll work.

<local:control x:Name="control"  
               CellValue="{Binding Path=CellNo,
                                   RelativeSource={RelativeSource AncestorType={x:Type Window}}, 
                                   Mode=TwoWay,
                                   UpdateSourceTrigger=PropertyChanged}">

<local:control x:Name="control"  
               CellValue="{Binding Path=CellNo,
                                   ElementName=myWindow,
                                   Mode=TwoWay,
                                   UpdateSourceTrigger=PropertyChanged}">

You may also need to set the the DataContext of control to itself

public control()
{
    InitializeComponent();
    this.DataContext = this;
    //...
}

Update

You can download a sample application of this here.

Otherwise, here's my full sample code.

MainWindow.xaml

<Window x:Class="DependencyPropertyInsideUserControl.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:DependencyPropertyInsideUserControl"
        Title="MainWindow" Height="350" Width="525"
        Name="myWindow">
    <Grid>
        <local:control x:Name="control"
                       CellValue="{Binding Path = CellNo, Mode=TwoWay, ElementName=myWindow, UpdateSourceTrigger=PropertyChanged}"/>
            <Button Content="Update CellNo" Height="23" HorizontalAlignment="Left" Margin="185,149,0,0" Name="button1" VerticalAlignment="Top" Width="94" Click="button1_Click" />
    </Grid>
</Window>

Mainwindow.xaml.cs

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        CellNo = "Hello";
    }
    private void button1_Click(object sender, RoutedEventArgs e)
    {
        CellNo = "Hi";
    }
    private string m_cellNo;
    public string CellNo
    {
        get
        {
            return m_cellNo;
        }
        set
        {
            m_cellNo = value;
            OnPropertyChanged("CellNo");
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

control.xaml

<UserControl x:Class="DependencyPropertyInsideUserControl.control"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <TextBox Text="{Binding Path = CellValue}" 
                 Name="textBox2" />
    </Grid>
</UserControl>

control.xaml.cs

public partial class control : UserControl
{
    public string CellValue
    {
        get { return (string)GetValue(CellValueProperty); }
        set { SetValue(CellValueProperty, value); }
    }
    // Using a DependencyProperty as the backing store for LimitValue.  This enables animation, styling, binding, etc...    
    public static readonly DependencyProperty CellValueProperty =
        DependencyProperty.Register("CellValue", typeof(string), typeof(control), new FrameworkPropertyMetadata
        {
            BindsTwoWayByDefault = true,
        });
    public control()
    {
        InitializeComponent();
        this.DataContext = this;
        CellValue = "Test";
    }
}
like image 107
Fredrik Hedblad Avatar answered Nov 15 '22 22:11

Fredrik Hedblad