Setting a custom property within a WPF/Silverlight page

Question

This sounds like it should be simple. I have a Page declared in XAML in the normal way (i.e. with "Add new item...") and it has a custom property. I\'

Answer 1

I just tried to do the same with some different intent, though.

The real answer actually is: You need the WPF convention for Set-methods done right. As outlined here: http://msdn.microsoft.com/en-us/library/ms749011.aspx#custom you have to define the SetXxx and GetXxx methods if you are about to definde an attached property named Xxx.

So see this working example:

public class Lokalisierer : DependencyObject
{
    public Lokalisierer()
    {
    }

    public static readonly DependencyProperty LIdProperty = 
        DependencyProperty.RegisterAttached("LId", 
                                            typeof(string), 
                                            typeof(Lokalisierer),
                                            new FrameworkPropertyMetadata( 
                                                  null,
                                                     FrameworkPropertyMetadataOptions.AffectsRender | 
                                                     FrameworkPropertyMetadataOptions.AffectsMeasure,
                                                     new PropertyChangedCallback(OnLocIdChanged)));

    private static void OnLocIdChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
    // on startup youll be called here
    }

    public static void SetLId(UIElement element, string value)
    {
      element.SetValue(LIdProperty, value);
    }
    public static string GetLId(UIElement element)
    {
      return (string)element.GetValue(LIdProperty);
    }


    public string LId
    {
        get{    return (string)GetValue(LIdProperty);   }
        set{ SetValue(LIdProperty, value); }
    }
}

And the WPF part:

<Window x:Class="LokalisierungMitAP.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:me="clr-namespace:LokalisierungMitAP"
Title="LokalisierungMitAP" Height="300" Width="300"
>
<StackPanel>
    <Label  me:Lokalisierer.LId="hhh">Label1</Label>
   </StackPanel>

BTW: You need also to inherit DependencyObject

Answer 2

You can set the property with a style:

<Page.Style>
    <Style TargetType="{x:Type wpfSandbox:TestPage}">
        <Setter Property="MyProperty" Value="This works" />
    </Style>
</Page.Style>

But it only works for dependency properties!

public static readonly DependencyProperty MyPropertyProperty = DependencyProperty.Register(
    nameof(MyProperty), typeof(string), typeof(Page),
    new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.AffectsRender));

public string MyProperty
{
    get { return (string)GetValue(MyPropertyProperty); }
    set { SetValue(MyPropertyProperty, value); }
}

Answer 3

You could declare your <Page> element to be a <TestPage> element instead:

<YourApp:TestPage 
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
  xmlns:YourApp="clr-namespace:YourApp"
  MyProperty="Hello">
</YourApp:TestPage>

That would do the trick, but you lose InitializeComponent() and the standard designer stuff. Design mode still seems to work flawlessly, though, but I haven't extensively tested this.

UPDATE: This compiles and runs, but does not actually set MyProperty. You also lose the ability to bind event handlers in XAML (although there may be a way to restore that which I am unaware of).

UPDATE 2: Working sample from @Fredrik Mörk which sets the property, but does not support binding event handlers in XAML:

Code-behind:

namespace WpfApplication1
{
    public partial class MainWindow : Window
    {
        protected override void OnActivated(EventArgs e)
        {
            this.Title = MyProperty;
        }      

        public string MyProperty { get; set; }
    }
}

XAML:

<WpfApplication1:MainWindow
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:WpfApplication1="clr-namespace:WpfApplication1" 
    Title="MainWindow" 
    Height="350" 
    Width="525"
    MyProperty="My Property Value"> 
</WpfApplication1:MainWindow>

Answer 4

This worked for me

<Window x:Class="WpfSandbox.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfSandbox"        
    xmlns:src="clr-namespace:WpfSandbox" 
    Title="MainWindow" Height="350" Width="525"
    src:MainWindow.SuperClick="SuperClickEventHandler">
</Window>

So this may work for the original question (didn't try). Note xmlns:src.

<Page x:Class="WpfSandbox.TestPage"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:local="clr-namespace:WpfSandbox"        
  xmlns:src="clr-namespace:WpfSandbox" 
  src:TestPage.MyProperty="MyPropertyValue">
</Page>