CODEWITHSUNDEEP
wpfxamldata-binding
Guillaume Slashy
Guillaume Slashy

Reputation: 3624

Binding to a 2nd properties if the 1st one is "undefined"

I won't copy/paste my whole xaml file. It will be too long to explain it but here is what is interesting : I got a Binding of a Property "Name"

<TextBlock Text="{Binding Name}"/>

The thing is that sometimes, my item doesn't have a "Name" property. It doesn't crash but I simply got an empty Text in my TextBlock

What I would to do, if Name is empty, is to be binded to "nothing", just {Binding}. This will display my Object name and it will be perfect !

Thanks in advance for any help, and sorry if it is a noobie question :(

Upvotes: 8

Views: 1637

Answers (4)

Dan Bryant
Dan Bryant

Reputation: 27495

What you want here is a PriorityBinding.

In particular, it would look something like (exact syntax may need some verification):

         <TextBlock>
            <TextBlock.Text>
                <PriorityBinding>
                    <Binding Path="Name"/>
                    <Binding />
                </PriorityBinding>
            </TextBlock.Text>
         </TextBlock>

Note that this specifically falls back when the Name property is not available on the object being bound; if the Name property has an empty string value, I believe it will still use that empty value.

Upvotes: 7

brunnerh
brunnerh

Reputation: 184506

You can apply a style with a DataTrigger:

<TextBlock>
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Setter Property="Text" Value="{Binding Name}"/>
            <Style.Triggers>
                <!-- In this binding you could inject a converter which checks for more than null -->
                <DataTrigger Binding="{Binding Name}" Value="{x:Null}">
                     <Setter Property="Text" Value="{Binding}"/>
                </DataTrigger>
            <Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>

Upvotes: 3

tier1
tier1

Reputation: 6433

This is theoretical but..

I would create a custom style and target all of your textblocks. Inside your style, you could set a default text value. If your binding doesn't override the style, your default value will be used.

Style x:Key="TwitterTextBoxStyle" TargetType="{x:Type TextBox}">
    <Setter Property="Text" Value="" />

Upvotes: 0

Bj&#246;rn
Bj&#246;rn

Reputation: 3418

If you don't have to bind to the object type name you could use TargetNullValue which will give you a default value if the bound property is null, like this:

<TextBlock Text="{Binding Name, TargetNullValue=Default}" />

If you really want the object type name I would suggest writing a Converter (implement IValueConverter). Let me know if you want a sample converter.

Upvotes: 0

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