How can WPF objects deriving from Freezable be frozen in XAML?

Question

Many types in WPF derive from Freezable. It provides immutability to mutable POCO objects and allows for improved performance in certain situations.

So my question is, how can I freeze objects in XAML markup?

(Note that I have posted a similar but different question too).

Cockadoodledoo

Does this really improve performance? Is there a way to measure the differences between a WPF app without and with po:Freeze="True" set all over the place? – Rocher

@AlexandruDicu it can make a big difference depending upon what your so is doing. To verify, you'd need to get before and after CPU traces and compare them. – Cockadoodledoo

Answer 1

To freeze a Freezable object declared in markup, you use the Freeze attribute defined in XML namespace http://schemas.microsoft.com/winfx/2006/xaml/presentation/options.

In the following example, a SolidColorBrush is declared as a page resource and frozen. It is then used to set the background of a button.

<Page 
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options" 
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="po">

  <Page.Resources>
    <!-- This brush is frozen -->
    <SolidColorBrush x:Key="MyBrush" po:Freeze="True" Color="Red" />
  </Page.Resources>

  <!-- Use the frozen brush -->
  <Button Background="{StaticResource MyBrush}">Click Me</Button>

</Page>

Source: Freezable Objects Overview

Beauty

Shouldn't the last attribute be mc:Ignorable="po"? – Dipietro

Answer 2

Add this to your xaml namespace declarations:

xmlns:po="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="po"

then, in your freezable objects, include this attribute

po:Freeze="True"

Quadri

Where does the 'mc' namespace come from? – Cockadoodledoo

Oh, i think i missed that. Fixed it now. – Quadri