TwoWay binding to Resources

11-06-2009 3:32 PM |

Hi All,

           Can anyone explain why resources in ItemsControl allow twoway binding while regular resources are oneway only?

eg: Paste the following into xamlpad http://silverlight.services.live.com/invoke/6655/XamlPadSL3/iframe.html 

Thanks

slyi

<Grid  
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sys="clr-namespace:System;assembly=mscorlib">
    <Grid.Resources>
        <ItemsControl x:Key="ResVars">
            <sys:Double >32</sys:Double>
        </ItemsControl>
        <sys:Double x:Key="Dbl" >32</sys:Double>
    </Grid.Resources>
    <Grid x:Name="LayoutRoot">
        <StackPanel>
            <Slider Value="{Binding Items[0], Source={StaticResource ResVars},Mode=TwoWay}"    Maximum="100" />
            <TextBlock Text="{Binding Items[0], Source={StaticResource ResVars}}"/>
            <!--<Slider Value="{Binding  Source={StaticResource Dbl}, Mode=TwoWay}"   Maximum="100" />                     
            <TextBlock Text="{Binding  Source={StaticResource Dbl}}"/>-->
        </StackPanel>
    </Grid>
</Grid>

Re: TwoWay binding to Resources

11-06-2009 3:47 PM |

If you load that in visual studio you will get the error message that two way bindings require a path. Here is the best explanation I've seen on that:

The problem is as you have described, you need a path, a binding without a path binds to the current datacontext. But in this situation, even if you could have a two-way binding, updating the source could only replace the datacontext - it couldn't actually set the value somewhere else because it doesn't know where it came from.

Re: TwoWay binding to Resources

11-06-2009 4:15 PM |

ok but it still doesnt twoway bind when i set the datacontext

<Grid  
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    DataContext="{Binding RelativeSource={RelativeSource Self}}" >
    <Grid.Resources>
        <sys:Int32 x:Key="Dbl" >32</sys:Int32>
    </Grid.Resources>
    <Grid x:Name="LayoutRoot" >
        <StackPanel>
            <Slider Value="{Binding Path=Resources.Values[0], Mode=TwoWay}"   Maximum="100" />                     
            <TextBlock Text="{Binding Path=Resources.Values[0]}"/>
        </StackPanel>
    </Grid>
</Grid>

Re: Re: TwoWay binding to Resources

11-06-2009 5:15 PM |

It won't two way bind without the path. The datacontext isn't the issue.

Re: Re: Re: TwoWay binding to Resources

11-06-2009 5:16 PM |

What is it that you're really trying to do? If you really need to bind to a resouce just put the double in a class and you'd be done.