WPF UserControl Page Binding Issue

isa turgut 20

Hello everybody,
I have a really basic question actually about WPF binding in my code. The problem is that I have a WPF page which inherited from a base class which inherits from UserControl and the base class implements INotifyPropertyChanged interface.

So that in my child class which is a page, I declare props and these props calling OnPropertyChanged method. Then I expect that after I bind the prop to the UI control then after the prop changed then it should update the UI side, but when I debug the code then the prop changed, PropertyChanged event comes null.

When I bind the prop in UI side I use ElementName= CodeBehind which the name of xaml, Path= propName, Mode=TwoWay,

By the way, the problem occurs only one project of mine, I mean, in the other project which is the same structure, it does not occur.

What is the problem of occuring that problem in WPF? Some of my research is saying that xaml does not find the props context, so that I call the code which is this.Context = this, but it does not work. What is the reason?

Hongrui Yu-MSFT 3,015 Reputation points Microsoft Vendor

2024-11-18T02:15:18.0266667+00:00
Hi,@isa turgut. Welcome to Microsoft Q&A.

This may be related to the location of the UI. You could try to set the DataContext directly for the UI control.

<TextBlock x:Name="MyTextBlock" Text="{Binding Path=Prop,Mode=TwoWay}" Width="200" Height="30"></TextBlock>

MyTextBlock.DataContext = this;

If the above solution still can't fix it, please provide the code of the minimum viable program.

isa turgut 20

Sure, please find the program below,

<local:BaseClassExample x:Class="WpfApp1.UserControl1"
             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"
            xmlns:local="clr-namespace:WpfApp1"
            d:DesignHeight="450" d:DesignWidth="800" x:Name="Codebehind">
    <local:BasePage>
        <Grid Background="Aqua">

            <TextBlock x:Uid="txtBlock"
                       Text="{Binding ElementName=Codebehind, Path=MyProperty, Mode=TwoWay}"
                       FontSize="50"
                       FontWeight="ExtraBold"></TextBlock>

            <Button Click="Button_Click"
                    Width="100"
                    Height="100"
                    Background="Bisque">Button Deneme</Button>

        </Grid>
    </local:BasePage>
    
</local:BaseClassExample>

In the above, I put the page xaml codes, I will provide BaseClassExample and BasePage codes too. Summarily, When I press the button then Button_Click event is fired, then in the event method, I change MyProperty value text and I am expecting that TextBlock is updated with the text that I bind it. But when I put breakpoint to the OnPropertyChange method that we call in the Set method of MyProperty field, I see that PropertyChanged event is null.

Showing problem in debug mode

Please find the used other class definitions below,

BaseClassExample

public class BaseClassExample : UserControl, INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged;

protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

}

BasePage.xaml

<local:BaseClassExample x:Class="WpfApp1.BasePage"
    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"
    xmlns:local="clr-namespace:WpfApp1"
    mc:Ignorable="d"
    d:DesignHeight="450"
    d:DesignWidth="800"
                        x:Name="CodeBehind">

    <Border Width="800"
            Height="600"
            HorizontalAlignment="Center">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="86" />
                <RowDefinition Height="514" />
            </Grid.RowDefinitions>
            <Border Grid.Row="0">
                <Border.Effect>
                    <DropShadowEffect BlurRadius="20"
                                      Opacity="0.25"
                                      ShadowDepth="1"
                                      Color="#00000029" />
                </Border.Effect>
                <Grid x:Name="HeaderPanel"
                      Height="86">
                    <Grid.Background>
                        <SolidColorBrush Color="#FFFFFF" />
                    </Grid.Background>
                </Grid>
            </Border>
            <Grid Grid.Row="0">
                <ContentPresenter Content="{Binding HeaderContent, ElementName=CodeBehind}" />
            </Grid>
            <Grid Grid.Row="1"
                  Uid="MainGrid">
                <ContentPresenter Uid="MainInnerGrid"
                                  Content="{Binding InnerContent, ElementName=CodeBehind}" />
            </Grid>
        </Grid>
    </Border>
</local:BaseClassExample>

BasePage.xaml.cs

public partial class BasePage : BaseClassExample
{

    #region HeaderContent 
    public static readonly DependencyProperty HeaderContentProperty =        DependencyProperty.Register("HeaderContent", typeof(FrameworkElement), typeof(BasePage));
    public FrameworkElement HeaderContent
    {
        get
        {
            return (FrameworkElement)GetValue(HeaderContentProperty);
        }
        set
        {
            SetValue(HeaderContentProperty, value);
        }
    }
    #endregion HeaderContent

    #region InnerContent
    public static readonly DependencyProperty InnerContentProperty = DependencyProperty.Register("InnerContent", typeof(FrameworkElement), typeof(BasePage));
    public FrameworkElement InnerContent
    {
        get
        {
            return (FrameworkElement)GetValue(InnerContentProperty);
        }
        set
        {
            SetValue(InnerContentProperty, value);
        }
    }
    #endregion

    #region TopContent
    public static readonly DependencyProperty TopContentProperty = DependencyProperty.Register("TopContent", typeof(FrameworkElement), typeof(BasePage));
    public FrameworkElement TopContent
    {
        get
        {
            return (FrameworkElement)GetValue(TopContentProperty);
        }
        set
        {
            SetValue(TopContentProperty, value);
        }
    }
    #endregion

    public BasePage()
    {
        InitializeComponent();
    }
}

Accepted answer

Hongrui Yu-MSFT 3,015 Reputation points Microsoft Vendor

2024-11-20T02:32:00.21+00:00
Hi,@isa turgut.

You used <local:BasePage> in UserControl1, you could directly set the DataContext for <local:BasePage>.

UserControl1.xaml

<local:BasePage x:Name="MyBasePage"> ... <TextBlock x:Uid="txtBlock" Text="{Binding Path=MyProperty, Mode=TwoWay}" FontSize="50" FontWeight="ExtraBold"></TextBlock> ... </local:BasePage>

UserControl1.xaml.cs

public UserControl1() { InitializeComponent(); MyBasePage.DataContext = this; this.Loaded += UserControl1_Loaded; }

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isa turgut 20 Reputation points

2024-11-21T19:11:59.65+00:00

Yes you are right, if I give Name to BasePage and set the page DataContext in codebehind then it works.

On the other hand, if I do not use ElementName in the Textblock and set Codebehind datacontext in the codebehind of page then it works too. I mean, I give Path and Mode only then put the code snippet Codebehind.Datacontext = this, and it works. if I give ElementName to the Textblock then it does not work even I set Codebehind.Datacontext = this, in codebehind side,

The question I wonder that why I must not use elementName in the xaml side and why it does not work with using ElementName?

isa turgut 20 Reputation points

2024-11-21T20:09:26.9433333+00:00

Thanks for your helps in advance.

Hongrui Yu-MSFT 3,015 Reputation points Microsoft Vendor

2024-11-22T02:45:44.64+00:00

Hi,@isa turgut.

I adjusted the answer to make it more accurate.

Regarding your question, it seems to be related to NameScope. You could find that ElementName becomes invalid if it exceeds the Grid scope(Template scope).

Here is a more detailed discussion of ElementName and NameScope, you could refer to it.
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