XAML Back to Basics #5: DisplayMemberPath

DisplayMemberPath

WPF DisplayMemberPath

XAML Basics Series Index Page

The next post in the series originally written by Beatriz Stollnitz. Original post available on Github.

DisplayMemberPath

As I’ve shown in previous posts, binding an ItemsControl to an IEnumerable data source is really easy (remember that ListBox and ComboBox derive from ItemsControl). With DisplayMemberPath it’s even easier for the scenario where you want to display only one property of each data item as text. Before DisplayMemberPath, this scenario required the use of a DataTemplate that would specify the property we’re interested in, like in the following xaml:

<Window.Resources>
    <DataTemplate x:Key="itemTemplate">
        <TextBlock Text="{Binding Path=Name}" />
    </DataTemplate>
</Window.Resources>

<ItemsControl ItemsSource="{StaticResource greekGods}" ItemTemplate="{StaticResource itemTemplate}" />

The Data Binding team realized that this was a very common scenario and could be simplified, which was the motivation for introducing the DisplayMemberPath property in ItemsControl. The scenario above can now be done in a single line of xaml:

<ItemsControl ItemsSource="{StaticResource greekGods}" DisplayMemberPath="Name" />

It’s that easy 🙂

The image below shows both versions of the ItemsControl, the one on the left is using DataTemplate and the one on the right is using DisplayMemberPath.

WPF Source Code

WPF

UWP/Uno Source Code

t whose value you’re interested … Continue reading“XAML Back to Basics #2: Binding Markup”

The next post in the series originally written by Beatriz Stollnitz. Original post available on Github.

What does “{Binding}” mean?

Most Bindings you see in samples have the Source and Path properties set. The Source property specifies the object you’re binding to and the Path specifies a property in that object whose value you’re interested in. I’ve seen several people get confused when encountering an empty Binding for the first time – “{Binding}”. It seems at first sight that we’re not giving the Binding enough information to do anything useful. This is not true and I will explain why. If you read my previous post you should understand that it is not necessary to set a Source in a Binding, as long as there is a DataContext set somewhere up in the tree. As for the Path, it should be left out when you want to bind to a whole object, and not only to a single property of an object. One scenario is when the source is of type string and you simply want to bind to the string itself (and not to its Length property, for example).

<Window.Resources>
    <system:String x:Key="helloString">Hello</system:String>
</Window.Resources>

<Border DataContext="{StaticResource helloString}">
    <TextBlock TextContent="{Binding}"/>
</Border>

Another common scenario is when you want to bind some element to an object with several properties.

<Window.Resources>
    <local:GreekGod Name="Zeus" Description="Supreme God of the Olympians" RomanName="Jupiter" x:Key="zeus"/>
</Window.Resources>

<Border DataContext="{StaticResource zeus}">
    <ContentControl Content="{Binding}"/>
</Border>

In this case, ContentControl does not know how to display the GreekGod data. Therefore you will only see the results of a ToString(), which is typically not what you want. Instead, you can use a DataTemplate, which allows you to specify the appearance of your data.

<Window.Resources>
    <local:GreekGod Name="Zeus" Description="Supreme God of the Olympians" RomanName="Jupiter" x:Key="zeus"/>
    <DataTemplate x:Key="contentTemplate">
        <DockPanel>
            <TextBlock Foreground="RoyalBlue" TextContent="{Binding Path=Name}"/>
            <TextBlock TextContent=":" Margin="0,0,5,0" />
            <TextBlock Foreground="Silver" TextContent="{Binding Path=Description}" />
        </DockPanel>
    </DataTemplate>
</Window.Resources>

<Border DataContext={StaticResource zeus}">
    <ContentControl Content="{Binding}" ContentTemplate="{StaticResource contentTemplate}"/>
</Border>

Notice that none of the Binding statements inside the DataTemplate has a Source. That is because a DataContext is automatically set to the data object being templated.

WPF Source Code

WPF

UWP/Uno Source Code

UWP

Update 31st August 2020

Uno sample has been updated to v3 of Uno and supports iOS, Android, Windows and MacOS.

WinUI with Uno and WinUI for Desktop samples added.

WinUI with Uno and WinUI Desktop Source Code

WinUI-Desktop

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