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WPF Persistency

, 3 Jan 2013 CPOL
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This article describes how to persist WPF dependency properties

Introduction

While looking for a way to persist state for a WPF application, I found the article WPF Control State Persistency from Tomer Shamam. Although the article was great and easy to use, I was inspired by a comment from Robert Cannon to try an alternate implementation.

The main differences are:

  • Automatic key generation
  • No need to explicitly load/save persisted data
  • No mode support (Memory/Persist)
  • Only one (static) dictionary for the whole project
  • Direct binding to back storage

Using the code

The following steps have to be done to use the code:

  • Copy attached file UserSettings.cs into your project
  • Add a namespace declaration to the XAML file xmlns:app="clr-namespace:WpfPersist".
  • Use the UserSettings markup extension (and provide default value) where appropriate.

The markup snippet below shows how to use the UserSettings markup extension to store Window Size and Position:

<Window x:Class="WpfPersist.Demo.Window1"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   xmlns:app="clr-namespace:WpfPersist"
   Title="WpfPersist.Demo"
   Height="{app:UserSettings Default=300}" 
   Width="{app:UserSettings Default=400}"
   Top="{app:UserSettings}" Left="{app:UserSettings}"
   >
   <Grid>
   ...
   </Grid>
</Window>

How it Works?

The main difference between this implementation and the one from Tomer is that I try to automatically derive a key for persistent storage. The snippet below shows how I do that for objects that derive from UIElement:

IUriContext uriContext = (IUriContext)serviceProvider.GetService
                            (typeof(IUriContext));
key = string.Format("{0}.{1}[{2}].{3}",
   uriContext.BaseUri.PathAndQuery,
   targetObject.GetType().Name, ((UIElement)targetObject).PersistId,
   targetProperty.Name);

Objects that have a parent in the logical tree (like ColumnDefinition) also can have the key automatically generated:

IUriContext uriContext = (IUriContext)serviceProvider.GetService
                            (typeof(IUriContext));
UIElement parent = (UIElement)LogicalTreeHelper.GetParent(targetObject);
int i = 0;
foreach (object c in LogicalTreeHelper.GetChildren(parent))
{
   if (c == targetObject)
   {
      key = string.Format("{0}.{1}[{2}].{3}[{4}].{5}",
         uriContext.BaseUri.PathAndQuery,
         parent.GetType().Name, parent.PersistId,
         targetObject.GetType().Name, i,
         targetProperty.Name);
      break;
   }
   i++;
}

Unfortunately I found no way to derive a key for GridViewColumn objects.
For debug builds, the code issues an assert on properties where no key can be generated. In release builds, the code silently ceases functioning.
To work around this, there is a Key property on the markup extension. Note that the key should be unique for the whole project and not only the XAML file. The snippet below shows how to apply the Key property:

<GridViewColumn
   DisplayMemberBinding="{Binding Mode=OneTime,Path=ProcessName}"
   Header="ProcessName"
   Width="{app:UserSettings Default=100, 
                Key=Window1.ListView0.Col0.Width }" />

Another difference between the two implementations is that I use an ApplicationSettingsBase derived internal class for persistent storage. The current implementation saves the data automatically when the main Window is closing. Meaning that there is no need to provide additional code to save/load the data.

Points of Interest

The biggest shortcoming of this implementation is that I found no way to persist ordering for GridViewColumn's.
For Winforms, the designers provided the DisplayIndex property on the DataGridViewColumn object that could be used for that, but in WPF there is no such thing. The WPF-Designers obviously felt that a modified Columns collection should be enough.

Another issue that nearly drove me nuts was the XmlnsDefinitionAttribute that Tomer is using. It took me quite a while to figure out that this attribute works only for code that is implemented in a different assembly.

If anyone finds a good solution to persist column ordering or finds a way to generate a key for the GridViewColumn property, I'm more than happy to hear about it.

Change Log

  • 7 Aug 2007: Initial Version
  • 3 Jan 2013: Update to VS2010 (recommended fix for VS-Designer)

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Reto Ravasio

Switzerland Switzerland
No Biography provided

Comments and Discussions

 
QuestionErrors and Warnings Pinmemberyolki201219-Nov-12 0:52 
AnswerRe: Errors and Warnings PinmemberFernando E. Braz22-Mar-13 7:02 
GeneralRe: Errors and Warnings Pinmemberc39209302910-Jun-14 11:13 
BugBug fix : avoid exception in design mode Pinmemberchprogmer6-Jun-12 3:12 
GeneralRe: Bug fix : avoid exception in design mode Pinmemberyolki201219-Nov-12 0:49 
why error
Error 3 Object reference not set to an instance of an object.
comes prograM RUNS Fine but this error comes in warning ang errors
 
and warning
 
Warning 2 'System.Windows.UIElement.PersistId' is obsolete: 'PersistId is an obsolete property and may be removed in a future release. The value of this property is not defined.'
 
is ther nay way to get rid of it.
GeneralRe: Bug fix : avoid exception in design mode Pinmemberchprogmer29-Nov-12 13:44 
NewsRe: Bug fix : avoid exception in design mode PinmemberReto Ravasio3-Jan-13 14:07 
SuggestionLicense Pinmemberchprogmer6-Jun-12 0:31 
GeneralBe carful with PersistId property because it is obsolete Pinmemberido.ran24-Jun-10 6:02 
GeneralRe: Be carful with PersistId property because it is obsolete PinmemberReto Ravasio24-Jun-10 11:55 
AnswerRe: Be carful with PersistId property because it is obsolete PinmemberReto Ravasio3-Jan-13 5:02 
GeneralAbout the "Settings" class PinmemberAvi Bueno19-Mar-10 14:09 
GeneralRe: About the "Settings" class PinmemberReto Ravasio21-Mar-10 14:13 
GeneralRe: About the "Settings" class PinmemberAvi Bueno9-Apr-10 11:20 
GeneralMaking sure owned windows are also persisted PinmemberAvi Bueno12-Aug-09 7:00 
AnswerRe: Making sure owned windows are also persisted PinmemberReto Ravasio12-Aug-09 9:37 
GeneralRe: Making sure owned windows are also persisted PinmemberAvi Bueno16-Aug-09 21:20 
GeneralKudos + UserSettings DesignTime bug fix PinmemberAvi Bueno11-Aug-09 5:41 
GeneralNice code! Help needed with radio btn persistence Pinmembermcvf4-Jun-09 11:40 
AnswerRe: Nice code! Help needed with radio btn persistence PinmemberReto Ravasio4-Jun-09 12:45 
GeneralBug PinmemberFly17-Aug-08 1:17 
GeneralRe: Bug PinmemberReto Ravasio19-Aug-08 13:15 
GeneralBug fix for hosting in VS2008 WPF designer PinmemberErwyn7414-Aug-07 5:05 
GeneralRe: Bug fix for hosting in VS2008 WPF designer PinmemberReto Ravasio15-Aug-07 7:38 
GeneralRe: Bug fix for hosting in VS2008 WPF designer PinmemberDmitriy Sinyagin17-Jul-08 18:40 

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