I have an ItemsControl that binds to a list of items. These items have a name and value property. The value property is of type Object to allow different datatypes to be used. To display the value property correctly I use a ContentPresenter with a datatemplate for every datatype I might use.
<ItemsControl ItemsSource="{Binding Items}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding Path=Name}"/>
<GridSplitter Width="1"
Grid.RowSpan="4" Grid.Column="1"
HorizontalAlignment="Stretch" VerticalAlignment="Stretch"/>
<ContentPresenter Grid.Column="2" Content="{Binding Value}">
<ContentPresenter.Resources>
<DataTemplate DataType="{x:Type System:String}">
<TextBox Text="{Binding Path=Content, RelativeSource={RelativeSource AncestorType={x:Type ContentPresenter}}}"
BorderThickness="0"/>
</DataTemplate>
<DataTemplate DataType="{x:Type System:Int32}">
<TextBox Text="{Binding Path=Content, RelativeSource={RelativeSource AncestorType={x:Type ContentPresenter}}}"
TextAlignment="Right"
BorderThickness="0"/>
</DataTemplate>
<DataTemplate DataType="{x:Type System:Double}">
<TextBox Text="{Binding Path=Content, RelativeSource={RelativeSource AncestorType={x:Type ContentPresenter}}}"
TextAlignment="Right"
BorderThickness="0"/>
</DataTemplate>
<DataTemplate DataType="{x:Type System:Boolean}">
<CheckBox IsChecked="{Binding Path=Content, RelativeSource={RelativeSource AncestorType={x:Type ContentPresenter}}}"
HorizontalAlignment="Center"/>
</DataTemplate>
</ContentPresenter.Resources>
</ContentPresenter>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
The ContentPresenter uses the correct datatype and works great. My problem is that editing these values does not have any effect on the bound items. I suspect it is because I bind to the content property of the ContentPresenter rather than directly to the Value. I've tried using the ContentPresenter like this:
<ContentPresenter Grid.Column="2" Content="{Binding}">
<ContentPresenter.Resources>
<DataTemplate DataType="{x:Type System:String}">
<TextBox Text="{Binding Value}"
BorderThickness="0"/>
</DataTemplate>
But this way the correct DataTemplate isn't selected and it just displays the Object instead of a String for example. I also tried to leave out the path in the binding of the DataTemplate like this:
<DataTemplate DataType="{x:Type System:String}">
<TextBox Text="{Binding}" BorderThickness="0"/>
</DataTemplate>
With this I get an exception telling me to use the Path or XPath attribute.
So my question is: how do I correctly bind to the Value so it displays with the right DataTemplate and that any editing of the values is applied to the bound item.
Btw for some reason the formatted code blocks in my question indent much more after the first line. I tried fixing it but I don't understand what's happening.
Best Answer
I think you'll benefit from reading about
DataTemplate
s. First, I'd advise you to have a good, long read of the Data Templating Overview page on MSDN. As I mentioned in my comments, you should not use aContentPresenter
in yourDataTemplate
s. From the linked page:The thing that you seem to be missing is how and what to data bind to from inside a
DataTemplate
. TheDataContext
of theDataTemplate
will automatically be set to an instance of the type specified in theDataType
property. Therefore, the properties that theDataTemplate
has access to will also depend on the type specified in theDataType
property. For example, you cannot do this, because astring
does not have aValue
property.Instead, for a
string
, you'd need to data bind to the wholeDataContext
value like this:Alternatively, if you had a class names
SomeClass
and that class has aValue
property, then you could do this:Now, because these
DataTemplate
s have been defined without setting theirx:Key
values, the Framework will automatically render the content of eachDataTemplate
whenever it sees an object of the relevant type (and no other, explicit templates set). So try this out and if you still have a problem, let me know.