What is a ContentPresenter?
What is a ContentPresenter?
The concept of ContentPresenter is quite simple - it is a placeholder for any XAML content and it can be used to insert content at runtime.
Join the DZone community and get the full member experience.Join For Free
In WPF there is an element called ContentPresenter, that is often used inside control templates, as well as inside the root application markup. The concept of ContentPresenter is quite simple – it is a placeholder for any XAML content and it can be used to insert content at runtime.
What I personally find it useful for is dynamic user interface, where there is no need to define a static UI structure at design time, but at runtime there should be some components that are either defined in the application XAML or in an external resource.
A content presenter is used via the ContentPresenter element: <ContentPresenter></ContentPresenter>. The content inside this element can be partially (or completely, although its value is lost in this case) defined inside the <ContentPresenter.Content></ContentPresenter.Content> element.
If you consider using the ContentPresenter element by defining the content from scratch, there is no need to include the Content element in the base XAML – it cannot be empty and running it so will cause an exception to be thrown. Once the content is set at runtime, the proper tag will be added automatically.
Let’s take a look at an example. Here is the base XAML for a window:
<Window x:Class="WPF_Test.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="380" Width="568" Loaded="Window_Loaded"> <Grid> <ContentPresenter Name="MyContent"> </ContentPresenter> </Grid></Window>
I am also setting a name for my ContentPresenter, so that I can access it from the code-behind. I did not define any default content, but if I would want to, I would use the following XAML structure:
<ContentPresenter Name="MyContent"> <ContentPresenter.Content> <Button>Click Me</Button> </ContentPresenter.Content></ContentPresenter>
Here is some sample XAML content to test the basic capabilities:
The namespace is required here. Although you can use namespace-less elements when explicitly defining the content directly in the application, a namespace indicator is required when the content is dynamically placed.
To load the content above, in the code behind I can use this sample code:
StringReader reader = new StringReader(File.ReadAllText("D:\\Temporary\\button.txt"));XmlReader xmlReader = XmlReader.Create(reader);MyContent.Content = (Button)XamlReader.Load(xmlReader);
In this specific example, I am loading the content shown above from a text file. I am then reading it as XML (since XAML is based on XML and the formatting is preserved). The XAML data is then assigned to the Content property for the specified ContentPlaceholder.
I am parsing it via the XamlReader, that will read the elements and assign them properly. Notice the fact that I am explicitly converting the XAML content to a Button. I need to do this so that the content is correctly rendered. Otherwise, an exception will be thrown.
You might be wondering – well, with the same success you could be using a stackpanel or a grid. But this is not always the case. When control templates are built, there is a well-defined element hierarchy and sometimes using a defined container is not a choice. A content presenter can be a holder for any controls and can be bound to the content from various elements via TemplateBinding, if used in a template.
Opinions expressed by DZone contributors are their own.