You may get an error of the form Cannot add content of type 'System.Windows.Style' to an object of type 'System.Windows.ResourceDictionary' when working with WPF and your first reaction would be "What?! Why not!?". Well, the issue is very simple, only it stems from another source entirely: you've just tried to add a Style with the same key as another previously entered style.
I believe this is something that any decent WPF programmer will laugh about, but there it is: I had this control derived from ContentControl and, of course, somewhere in the template I had a ContentPresenter. It all worked very well until I added a resizable option. I had two of these controls on the page, the first would contain a Grid, the other an ItemsControl. When I resized vertically the control, the ItemsControl would remain unchanged whether I made the height bigger or smaller. The Grid, though, would remain the same if enlarging the container and then squash when the size of the container got smaller than its auto size.As you have probably noticed, a lot of my recent posts have been about WPF. Having to do a demo in this new (for me) technology I had a lot of thing to learn and a lot of brick walls to hit. It was exciting, but also difficult, with new concepts that felt awkward, mind twisting. I even burst one day shouting "I hate WPF".I was trying to build a control that has a border around it only in design mode. You do have the static class DesignerProperties and its method GetIsInDesignMode(DependencyObject element) to detect that in code, and you do have a property DesignMode on Components, but one that is not a Dependency property. How can you detect DesignMode in XAML?I don't want to write a long blog entry, just to attract attention to this blog entry from Josh on WPF which is very concise, to the point and also directing to more complex articles that add more detail.The problem is moot. The StackPanel doesn't work like that. You need to use a DockPanel to make inner children of the Panel stretch vertically and make the Panel fill all available space. The elements inside should have DockPanel.Dock="Top" to fill only the space they require , then no Dock for the element(s) you want to stretch, then DockPanel.Dock="Bottom" for the rest of the elements. That's how you get that "Outlook feel", too.
I was trying to use the Infragistics WPF controls and got stuck in the XamComboEditor. I was setting its ItemsSource to a list of ComboBoxDataItem objects and I wanted to have none of them selected by default. I had tried SelectedIndex -1, SelectedItem {x:Null}, Value {x:Null} to no avail. By some ridiculous functionality, the XamComboEditor would select some item in the middle of the list.In order to customize controls the way you want, you can either use a DataTemplate, different specific ControlTemplate properties, use the properties that the controls publish, but in the end, to get it right, you must actually change the ControlTemplate of the control itself. The best practice is to use an external resource dictionary that contains a style that changes various properties and also, if needed, the ControlTemplate.
The problem there is that there is no way to partially change the control template. I mean, yeah, I could think of a few ways, but in the end is the same thing: you need to replace the control template completely. And now you have two ... err.. actually three problems.
First, there are ways of getting the default control template, with all the functionality (we are talking about one, two or even more pages of XAML) and change only what you want. It's not trivial, but it can be done, either by copying it from the published sources (like the Windows SDK or the Expression Blend SystemThemes folder) or by using a utility like ShowMeTheTemplate.
Second, there is the issue of control templates differing depending on the Windows theme. And therefore one must either accept that the application will only look one way for every theme and Windows operating system, or provide templates for all the themes available (there are 6 defaults and a generic fallback theme).
Now, there are many tutorials about how to do that, basically just create a Themes folder, change AssemblyInfo.cs to
[assembly: ThemeInfo(
ResourceDictionaryLocation.SourceAssembly, //where theme specific resource dictionaries are located
ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located
)]
, copy the xaml files (with certain names) there and change them as you see fit. There is a catch, though! This will only work on your custom controls. Default controls already have a template in the operating system theme, so you need to do one extra thing in order to overwrite them, and that is to write the following in the a parent control Resources block:
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="{ThemeDictionary [LibraryOrApplicationNamespace]}" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
otherwise it will NOT work.
You can get the same result by adding this to the static constructor of the control, provided you have access to the sources:
DefaultStyleKeyProperty.OverrideMetadata(typeof([MyControlClass]), new FrameworkPropertyMetadata(typeof(MyControlClass)));
One thing you also need to be aware of is that Visual Studio caches the themes. If you change them, especially if you do it outside visual Studio, you need to force a Rebuild of the project.
I've decided to write this entry before I could actually master these tools because I don't think I will afterwards (I'd be too old to type). So here it goes:
All of the tools above, except ReSharper and Blend are free to use.
So I wasted 15 minutes on trying to make a converter work within a TemplateBinding. Even if there is no error returned, the converter is never called. Funny, no?
I was trying to bind a property to the value of a property of the parent UserControl in WPF. When you google for it you get something pretty interesting: give a name to the user control right inside the user control XAML, then reference it with ElementName.
What I found after hours of torment was that this doesn't always work. I guess it only works up to the first item container in the logical tree and then stops. So that when I tried to use a property ImageSource of the user control in a Menu.Icon it failed!
My solution looks pretty ugly, but it does work in all cases!
<Image Source="{Binding RelativeSource={RelativeSource FindAncestor,AncestorType={x:Type Controls:MyUserControl}},Path=MainMenuImageSource}"
Width="16" Height="16"></Image>
In other words: find the ancestor of the type of your user control and use it as the RelativeSource of the binding.
Update: When I had more time to thing I realised that a MultiBinding needs a Converter, but a simple Binding also has a Converter and I guess that is what I should have used. I will update the post when I get to work on Monday.
public class SectionHeaderConverter:IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
List<ToolBarItem> list = new List<ToolBarItem>();
foreach (IEnumerable<ToolBarItem> collection in values)
{
foreach (ToolBarItem element in collection)
{
list.Add(element);
var toolBarSectionHeader = element as ToolBarSectionHeader;
if (toolBarSectionHeader != null)
{
foreach (var item in toolBarSectionHeader.Items)
{
list.Add(item);
}
}
}
}
return list;
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
<MultiBinding Converter="{StaticResource SectionHeaderConverter}">
<Binding Path="Items"/>
</MultiBinding>
<Menu
ItemsSource="{Binding ElementName=ToolBarCurrent,Path=Items}"
ItemContainerStyleSelector="{StaticResource MenuItemContainerStyleSelector}"
ItemTemplateSelector="{StaticResource MenuItemTemplateStyleSelector}"
></Menu>
ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(container);
var style = (Style) ic.FindResource("SectionStyle");
var ic = Helper.FindVisualParent<Grid>(container);The source for it is underneath.
.
public static TParentItem FindVisualParent<TParentItem>(DependencyObject obj)
where TParentItem : DependencyObject
{
DependencyObject current = obj;
while (current != null)
{
var tCurrent = current as TParentItem;
if (tCurrent != null)
return tCurrent;
current = VisualTreeHelper.GetParent(current);
}
return null;
}
In Windows Presentation Foundation all resources (like ImageSources or Resource packs) are relative to the namespace of the control. So if you have a folder Images that holds your application icons and you use (in the application XAML) an ImageSource of "Images/MyImage.png" it will work. But as soon as the XAML is moved somewhere in a UserControl in the Controls namespace of a library, the ImageSource becomes invalid. It would only work as "../Images/MyImage.png" or "/Images/MyImage.png", even if the Controls namespace is not a folder and the control is in a library, not in the application that runs it!Just yesterday I was struggling with the same issue, only this facette of it seems like a completely different bug. You see, I added this control to the library and everything worked fine EXCEPT the visual designer. It is known that the Visual Studio 2008 WPF designer is not the best possible piece of software, but this was one of those errors you don't know where it comes from.<HierarchicalDataTemplate DataType="{x:Type Code:League}" ItemsSource="{Binding Path=Divisions}">
<TextBlock Text="{Binding Path=Name}"/>
</HierarchicalDataTemplate> Somewhere in the Window declaration there was a xmlns:Code="clr-namespace:MyControls.Desktop.Code"which is the namespace of the test application for the control in the library.
So, I had just wasted a long time being stupid about a user control, but I had finally fixed everything and I was willing to try it out. Initially I had tested it by directly entering it in XAML, but now I wanted to add it to the toolbox and drag and drop it to the WPF form.