how to user RelativeSource ?

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Sesztak
Posts: 172
Joined: Fri Jun 24, 2016 2:19 am

how to user RelativeSource ?

Postby Sesztak » Tue Oct 04, 2016 4:55 am

Dear JS- Support,

in normal WPF enviroment if we want to databind some property to parent datacontext, we should do something like that:

<TextBlock Text="{Binding Path=DataContext.Property, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>

The problem is we've got error in CSHTML5 :
-Type 'RelativeSource' is used like a markup extension but does not derive from MarkupExtension.
-The property 'AncestorType' was not found in type 'RelativeSource'.
-The type 'x:Type' was not found.

So is it a Bug or an unsupported feature from your side ?

Anyway, how to bind to parent datacontext ? e.g. we have a DatagGrid with DataGridTemplateColumn and we would like to bind some property from DataGridTemplateColumn objects to itemSource = > to some property of Row object.

Thanks for your kind reply,
Best Regards,
Péter

TaterJuice
Posts: 80
Joined: Thu Mar 16, 2017 5:40 am

Re: how to user RelativeSource ?

Postby TaterJuice » Thu Oct 19, 2017 4:15 pm

Wow, this hasn't been answered since 2016?

Well, I'm having the same issue with the latest beta, 12.2. Halp?

It's listed on the supported features page: http://cshtml5.com/links/what-is-supported.aspx

I've found the following syntax via Intellisense in the XAML editor, but it won't compile either:

Code: Select all

IsChecked="{Binding Path=IsSelected, RelativeSource={RelativeSource Mode=TemplatedParent}}"


Still a very limited implementation, but maybe JS-Admin can enlighten us to what we're doing wrong.

JS-Support
Site Admin
Posts: 783
Joined: Tue Apr 08, 2014 3:42 pm

Re: how to user RelativeSource ?

Postby JS-Support » Fri Oct 20, 2017 2:35 am

Hi,

- The current version Beta 12.2 supports the following RelativeSource modes: Seft and TemplatedParent. The mode "AncestorType" is not yet supported (it is on the roadmap for the coming months).

- The design-time error "Type 'RelativeSource' is used like a markup extension but does not derive from MarkupExtension" was a bug and it will be fixed in the upcoming Beta 12.3.

- At design-time, the XAML preview sometimes did not show the bindings, even though they did work at runtime. This will be fixed in the upcoming Beta 12.3.


Here is the explanation of each supported RelativeSource mode:


  • Self

    Use "Self" if you want to bind one property of an element to another property on the same element. With this mode, the element on which the binding is applied will be the source of the binding.

    Here is an example:

    Code: Select all

    <TextBlock Text="{Binding Width, RelativeSource={RelativeSource Mode=Self}}" x:Name="TextBlock1" Width="200"/>

    In this example, the TextBlock will display the text "200", because the Text property is bound to the Width property.


    Please note that this is NOT the same as:

    Code: Select all

    <TextBlock Text="{Binding Width}" x:Name="TextBlock1" Width="200"/>

    The line above will NOT work because it will be looking for a property "Width" on the DataContext. By "DataContext" we mean the content of the property "TextBlock1.DataContext". The DataContext is an inherited property, which means that "TextBlock1.DataContext" will have the same value as the DataContext property of the parent of the TextBlock.


    An alternative way to achieve the same result as "Selft" is to use "ElementName". With "ElementName" you can tell it to use the element itself as the source of the binding. Here is an example:

    Code: Select all

    <TextBlock Text="{Binding Width, ElementName=TextBlock1}" x:Name="TextBlock1" Width="200"/>


  • TemplatedParent

    Use "TemplatedParent" if you are inside a ControlTemplate and you want to bind a property of an element to a property of the templated control.

    For example, consider the following XAML code:

    Code: Select all

    <Border>
        <Border.Resources>
            <Style x:Key="MyRoundButtonStyle" TargetType="Button">

                <!-- Set the default value for some properties of the button: -->
                <Setter Property="Background" Value="Gray"/>
                <Setter Property="Foreground" Value="Black"/>
                <Setter Property="Padding" Value="12"/>
                <Setter Property="Cursor" Value="Hand"/>
                <Setter Property="HorizontalContentAlignment" Value="Center"/>
                <Setter Property="VerticalContentAlignment" Value="Center"/>

                <!-- Define how the button will be rendered: -->
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="Button">
                            <Grid>
                                <Ellipse
                                    Fill="{Binding Background, RelativeSource={RelativeSource Mode=TemplatedParent}}"
                                    HorizontalAlignment="Stretch"
                                    VerticalAlignment="Stretch"/>
                                <ContentPresenter
                                    Content="{Binding Content, RelativeSource={RelativeSource Mode=TemplatedParent}}"
                                    HorizontalAlignment="{Binding HorizontalContentAlignment, RelativeSource={RelativeSource Mode=TemplatedParent}}"
                                    VerticalAlignment="{Binding VerticalContentAlignment, RelativeSource={RelativeSource Mode=TemplatedParent}}"/>
                            </Grid>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </Border.Resources>
        <Button x:Name="MyTemplatedButton"
                Content="OK"
                Style="{StaticResource MyRoundButtonStyle}"
                Width="50"
                Height="50"
                Background="Blue"
                Foreground="White"/>
    </Border>


    In the code above, we create a round button by creating a new style using a ControlTemplate. The "Fill" property of the ellipse has a binding to the "Background" property of the templated button.

    Please note that the two following lines are strictly equivalent:

    Code: Select all

    <Ellipse Fill="{Binding Background, RelativeSource={RelativeSource Mode=TemplatedParent}}"/>
    and

    Code: Select all

    <Ellipse Fill="{TemplateBinding Background}"/>

    The main advantage of the "Binding" syntax compared to the "TemplateBinding" syntax is that the former allows you to specify a "Converter" to convert the bound value via a class that inherits from IValueConverter.


Regards,
JS-Support


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