I remember reading a couple of weeks ago that it sometimes doesn't work inside templates, and I recently tried to bind things in two different windows and it couldn't find the name declarations, so I assumed that it was local to the namespace of the class and just bound by setting the datacontext instead. However, I'm really curious when I am able to use binding elementname and when I cannot, because it's far more convenient when it is possible.
edit: In reading that article, I found this to be interesting:
"For this reason, styles and templates both define their own XAML namescopes, independent of whatever location in an object tree where the style or template is applied."
if this is true, doesn't that mean that Binding ElementName should not work in templates at all? But then I definitely have some working bindings on ElementName within my templates. That is the most confusing part, why do some bindings randomly work inside the templates and others do not? It must have some method for trying to resolve the name even if it isn't in the template or same namescope
Basically you need to be in the same name scope (read this). Most UI elements are in the same tree sharing the same name scope, however there can be breaks and barriers (styles/templates) and if you have abstract objects like DataGrid columns they do not have a name scope at all.
I've been working with WPF long enough to guess when i'll run into problems and i know common areas but don't think there's an easy way to tell in all situations up-front.
if this is true, doesn't that mean that Binding ElementName should not work in templates at all? But then I definitely have some working bindings on ElementName within my templates.
Within is just fine, that is the same scope. The point here is that if you apply the template and they would not have their own scopes there would be conflicts.
e.g.
<Button/>
<Button/>
If we expand the ControlTemplate you would get something like:
<Border Name="bd" Background="{TemplateBinding Background}">...</Border>
<Border Name="bd" Background="{TemplateBinding Background}">...</Border>
Obviously we would get a name conflict.
Same for DataTemplates in ItemsControls, if you name controls in the template that name would conflict with the same control instance in the applied template of other items.
On another note, you can bind from inside a template to the outside because logically there can only be one instance with that name or you can give them a distinct precedence based on how "close" the name scope is, e.g.
<TextBox Name="tb" Text="Test"/>
<ItemsControl ItemsSource="ABC">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Text, ElementName=tb}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
Related
I'm trying to use the PropertyGrid component from PropertyTools to display information on an object. I can bind the object easily enough -- it's a property on my DataContext -- but one of the things that can't be derived from the object is the name that should be displayed in the tab header. (And I can't change that; the object I'm inspecting comes from a third party.) The proper name is a different property on my DataContext.
PropertyGrid has a way to change the way the tab header is displayed, by passing a DataTemplate to its TabHeaderTemplate property. But something bizarre happens inside of the template: my DataContext is gone, replaced by something else. When I try to say {Binding TabName} in the appropriate place inside the context, it errors out and tells me that TabName is not a valid property on class Tab. But my DataContext class isn't called Tab; that's something inside of PropertyTools's codebase!
I'm still new to WPF, so I have no clue what's going on here. Why is the in-scope DataContext that's perfectly valid in the rest of the XAML file being yoinked out from under me inside this template, and how can I fix it?
EDIT: Posting the XAML as requested. The template is literally just the simplest possible thing:
<UserControl.Resources>
<DataTemplate x:Key="HeaderTemplate">
<TextBlock Text="{Binding TabName}" />
</DataTemplate>
</UserControl.Resources>
And then further down the page,
<props:PropertyGrid
SelectedObject="{Binding Value}"
TabHeaderTemplate="{StaticResource HeaderTemplate}" />
But for some bizarre reason, in the template it's trying to interpret the binding inside the wrong DataContext!
In this case, just be sure to specify the source in your binding. There are a few ways to do this. One is to use the RelativeSource property of the Binding. Another is to use ElementName
Give your UserControl this attribute:
x:Name="Root".
Then change your binding to use it
<TextBlock Text="{Binding ElementName=Root, Path=DataContext.TabName}" />
Or use this:
<TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type local:MyUserControl}}, Path=DataContext.TabName}"/>
I have a grid that I am trying to hook up a visibility converter to. I have a class set up in the HelperObjects namespace, but for some reason the xaml is not picking up the reference. The error message is "The resource BoolToVisConverter could not be resolved" Why won't the xaml pull in this resource? I am sure I am doing something ridiculous here...
Here is the xaml:
xmlns:HelperObjects="clr-namespace:foo.HelperObjects"
...
<Grid Visibility="{Binding isZoneTwoVisible, Converter={StaticResource BoolToVisConverter}}">
The error message is indicating that the resource identified by the key BoolToVisConverter, to which you're trying to bind, cannot be found.
The most likely explanation is that you haven't declared that resource within a scope that can be accessed by your xaml. You'll want to create a StaticResource with a key matching the name you're referencing, within a Resources section of your xaml, the exact location may vary depending on your needs/structure.
Assuming you're doing this within a Window, you could do something like:
<Window>
<Window.Resources>
<BooleanToVisibilityConverter x:Key="BoolToVis"/>
</Window.Resources>
<Grid Visibility="{Binding isZoneTwoVisible, Converter={StaticResource BoolToVis}}">
<--...Content...-->
</Grid>
</Window>
Note: I haven't included your namespace in front of the BooleanToVisibilityConverter because this is a class which already exists within the framework.
It may be the case you require slightly different behaviour, or don't have access to that class, in which case you may need to add your namespace when defining the resource, e.g. <HelperObjects:BooleanToVisibilityConverter x:Key="BoolToVis"/>
Potentially useful further info about static resources: https://learn.microsoft.com/en-us/dotnet/framework/wpf/advanced/staticresource-markup-extension
Try to specify the converter in UserControlResources or even parent level Grid Resources. Assuming you are using a UserControl.
And your code is unclear as of where you are defining the StaticResource BoolToVisConverter. But generally heres the process.
Look at this sample code below to define your StaticResorce in the UserControl Resources section. Make sure you set the DataContext where isZoneTwoVisible is residing. I am hoping you implemented ImplementINotifyPropertyChanged and said PropertyChanged on your isZoneTwoVisible or isZoneTwoVisible is a DependencyProperty. Note: BooleanToVisibilityConverter is a class that implements an IValueConverter or if your property is a bool you don't even need that class.
<UserControl.Resources>
<BooleanToVisibilityConverter
x:Key="boolToVisibility"></BooleanToVisibilityConverter>
</UserControl.Resources>
You did all the things said above and it still dosen't work, sometimes I specify the relative Source hoping its residing in a UserControl.
Visibility="{Binding isZoneTwoVisible,Converter={StaticResource boolToVisibility},RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=UserControl}}">
In MainWindow we have:
<HeaderedContentControl
Content="{Binding Path=Workspaces}"
ContentTemplate="{StaticResource WorkspacesTemplate}"
Header="Workspaces"
Style="{StaticResource MainHCCStyle}"
/>
In the resources:
<DataTemplate x:Key="WorkspacesTemplate">
<TabControl
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding}"
ItemTemplate="{StaticResource ClosableTabItemTemplate}"
Margin="4"
/>
</DataTemplate>
And in the article says:
A typed DataTemplate does not have an x:Key value assigned to it, but
it does have its DataType property set to an instance of the Type
class. If WPF tries to render one of your ViewModel objects, it will
check to see if the resource system has a typed DataTemplate in scope
whose DataType is the same as (or a base class of) the type of your
ViewModel object. If it finds one, it uses that template to render the
ViewModel object referenced by the tab item's Content property.
My question is:
How does the template know that the type is a collection of workspaces (WorkspaceViewModel)?
It doesn't need to, in the code you've posted. In your sample, you have given a strict value to your content template: you've explicitly used {StaticResource WorkspacesTemplate}, and so a resource with the key of "WorkspacesTemplate is looked up.
Because you've explicitly set the template, it doesn't matter what the intended type is: it'll try to display any object in your Content using the template you've set - with varying degrees of success if you use a type that doesn't match!
In the alternate method you mention - with a "typed DataTemplate", you would declare your datatemplate with <DataTemplate DataType="{x:Type l:WorkSpace}" />. Note that there is no x:Key (and also that I've assumed you have a namespace l mapped to your local code). What happens here is that WPF automatically sets the key of your resource to the DataType (important to note: a resource key doesn't have to be a string!).
Then, when you declare your HeaderedContentControl, you can leave out setting the ContentTemplate. At runtime, when the control is rendered, WPF will check the type of the Content object and find that it is WorkSpace, and it'll then look up a resource with x:Key="{x:Type l:WorkSpace}" - which will match your typed template.
This is a useful way of making consistent representations of data throughout your application, since a typed DataTemplate will be used automatically by any content-presenting control throughout your application.
WPF doesn't really care about the concrete type, it's just need to be some IEnumerable of something, WPF uses the type descriptor to know what the ui binding with.
In my DB I have a table that contains different items of userControls with the attributes "ClassName", "AssemblyName" and "NameSpace" which are necesarry to init the instances using reflection.
My Idea was To get this collection from the DB, set the collection as the data-context and dynamically load these usercontrols into a tabcontrol. I could use a "tabItem" which would contain it and in runtime in the code behind load it. I guess it would be really handy and fancy if it could be done directly from XAML in a template.
I've been googleling for something similar, but found nothing without using code behind.
I was thinking something like the following
<TabControl.ContentTemplate>
<DataTemplate>
<xxxControl ClassName="{Binding ClassName}" AssemblyName="{Binding AssemblyName}" NameSpace="{Binding NameSpace}" />
</DataTemplate>
</TabControl.ContentTemplate>
I could make such a custom "xxxControl" but it would be a waste of time if something like that already exists. This way The GUI could be completly generated by the parameters in the DB.
You can do a lot of things in XAML using markup extensions, in this case you could create one that instantiates controls from the given information. For that it needs some dependency properties that can be bound, and in ProvideValue it would then get the assembly, construct the full name and instantiate it.
Usage:
<DataTemplate>
<me:Instance Assembly="{Binding AssemblyName}"
NameSpace="{Binding NameSpace}"
Class="{Binding ClassName}"/>
</DataTemplate>
Obviously you still have code-behind, but that is how it should be, imperative code does not belong in XAML at all.
Also i doubt that your data-base should contain information about UI controls...
Ugh. Don't control your UI from the database directly. The closest you should come (assuming you can't make significant architecture changes) IMO would be to load your DB entries into an IObservable in your VM and use a DataTemplateSelector to translate your collection into UI controls.
I am trying the following in my WPF application:
Structure of XAML elements.
DataTemplate[Data Type 'A']
Grid
Broder
TextBlock
I want to bind the text block's text property to a "string" which is derived from my "Users" class which is referenced in the resource dictionary of the XAML.
So in the above structure since the DataTemplate gets the feed from data type 'A'.
I want to assign the datacontext(Users) to the grid and bind the string to the textblock.
Is there a way i can achieve this ,since all my trials which include assigning the datacontext to the Grid or Border or TextBlock doesn't work.
Can any one suggest me or correct me if my approach is wrong here ?
This markup should suffice:
<DataTemplate DataType="{x:Type local:A}">
<Grid DataContext="{Binding Path=Users}">
<Border>
<TextBlock Text="{Binding Path=PropertyOnUsers}"/>
</Border>
</Grid>
</DataTemplate>
Make sure you have the namespace declared at the top of your Xaml. For whatever reason, WPF doesn't always automatically infer the template from the type if you don't use {x:Type ...}.
From there it should be straight forward.
If Users is a collection, you will have to drill into the collection to get a specific instance of User.
By the way, if you are using Visual Studio, you can use the Output window to debug binding issues.