I have the following XAML:
<Grid>
<Grid.RowDefinitions>
...
</Grid.RowDefinitions>
<DataGrid Grid.Row="0" ...>
<DataGrid.Columns>
...
</DataGrid.Columns>
</DataGrid>
<DockPanel Grid.Row="2">
<CheckBox x:Name="DisplayMarkers" DockPanel.Dock="Top" Content="Display Data Points?"
Margin="8,5,0,5" d:LayoutOverrides="Height" HorizontalAlignment="Left" IsChecked="False" />
<vf:Chart DockPanel.Dock="Top" ScrollingEnabled="False" ZoomingEnabled="True" ToolBarEnabled="True">
<vf:DataSeries AxisYType="Secondary" RenderAs="Line" DataSource="{Binding CdTeRoughnessList}"
XValueType="DateTime"
MarkerEnabled="{Binding ElementName=DisplayMarkers, Path=IsChecked}" Color="Navy"
LegendText="Roughness Std. Dev.">
This binding is failing: MarkerEnabled="{Binding ElementName=DisplayMarkers, Path=IsChecked}"
I'm trying to bind to the IsChecked property on my Checkbox named 'DisplayMarkers". When I run this, in debug mode in VS 2010, the output window shows the binding is failing. It can't find the element named 'Checkbox'. Could anyone tell me why?
The error I'm getting from VS is:
System.Windows.Data Error: 4 : Cannot find source for binding with reference
'ElementName=DisplayMarkers'. BindingExpression:Path=IsChecked; DataItem=null; target element is 'DataSeries' (Name=''); target property is 'MarkerEnabled' (type 'Nullable`1')
You might not have a namescope where you try to bind, you could try to replace the ElementName construct with Source={x:Reference DisplayMarkers}.
The gist of it is that if you have elements in XAML which are not in the visual or logical tree you will not be able to use certain bindings like RelativeSource and ElementName, I suspect that DataSeries is not in any tree either (it sure sounds like it's abstract).
For a workaround for potential cyclical dependency errors see: https://stackoverflow.com/a/6858917/546730
I'm guessing that the writer of Chart, when deriving from FrameworkElement or whatever, failed to realize that they needed to add any child elements to the logical tree either manually or through an override. You don't get that for free when deriving.
Breaking the logical tree breaks the ability of children to bind by ElementName.
If you are the author of the Chart object, you can see this related question and answer.
For other readers, another possible cause is using a UserControl instead of a custom control for what's in the role of vf:Chart, above. I wrote a split button (in the role of the chart) and changing it from a UserControl to a custom control got my ElementName binding working.
Related
I was solving Windows Phone 8.1 ListView wobbling problem and had code like below, however, once I add the ItemTemplate, the contents of the List cannot be seen, I'm wondering why and how to fix the problem.
<ListView
Grid.Row="1"
x:Name="ListViewEvents"
Loaded="OnListViewEventsLoaded"
ItemsSource="{Binding xx}"
ItemTemplateSelector="{StaticResource xx}"
ItemContainerStyle="{StaticResource xx}"
IsItemClickEnabled="True">
<ListView.ItemTemplate >
<DataTemplate >
<Grid Width="{Binding ActualWidth, ElementName=EventsListGrid}" />
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
Your Width binding is trying to read the ActualWidth property of an element in your XAML named EventsListGrid, but there's no such element in the sample code you've provided. As such, the binding engine is unable to set the Width property on your grid, most likely setting it to some unset/NaN value. At least I can confirm this when setting up a similar case as the one you provided and inspecting in Snoop the ListViewItem containers generated for each item in the test collection bound to the ListView. Perhaps you want to set the element name to ListViewEvents in this case or some other parent element not shown in the example?
I have successfully used ProxyElement to pass Data Context of my Data Grid to DataGridColumnHeaders. However, I am trying out something new and I just can't figure out what I am doing wrong over here.
Here is what I am trying to do: I am creating a UserControl and associating it to my ViewModel in my Resources file (see Resources.xaml code snippet below).
Resources.xaml:
<ResourceDictionary
xmlns:myVm="clr-namespace:..."
xmlns:myUserControl="clr-namespace:...">
<DataTemplate DataType={x:Type myVm:DummyModel}">
<myUserControl:DummyUserControl />
</DataTemplate>
</ResourceDictionary>
Now in my UserControl, I have a DataGrid with a DataGridComboBoxColumn. I am trying to access my data context to set its item source and in the past I was able to do it using proxy element. This time however I am not able to do so. (See DummyUserControl.xaml code snippet below)
DummyUserControl.xaml:
<UserControl x:Class="Client.MyControl.DummyUserControl"
...>
<UserControl.Resources>
<FrameworkElement x:Key="ProxyElement" x:Name="ProxyElement"
DataContext="{Binding}" />
</UserControl.Resources>
<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding Products}">
<DataGridComboBoxColumn
Header="Company"
ItemsSource="{Binding Path=DataContext.ProductCompanies,
Source={StaticResource ProxyElement}}"
DisplayMemberPath="Name" SelectedValuePath="Id"
SelectedValueBinding="{Binding CompanyId}" />
</DataGrid>
</UserControl>
When I do this, my binding fails with the following message:
System.Windows.Data Error: 3 : Cannot find element that provides DataContext.
BindingExpression:(no path); DataItem=null; target element is 'FrameworkElement'
(Name='ProxyElement'); target property is 'DataContext' (type 'Object')
I have no idea what to do here. I remember reading that the datacontext for a datatemplate is automatically set, so I have no idea why the data context is null in this case. To prove it is null, I also tried setting the binding in the code-behind file and added a breakpoint to check its value (which was null).
Can anyone suggest what to do here?
Edit 1
I have also tried the following approaches:
Remove ProxyElement altogether and see if it can detect DataContext. To no surprise, this failed.
Tried binding to the templated parent. Fail.
Tried binding to the UserControl itself. Fail.
I also tried referencing the data context of the parent item where this view model is going to be displayed, which is in a TabItem of a TabControl.
All of the alternate bindings gave me same error as the error above.
Here is a (working but not preferred) solution to this problem. You will realize why it is not preferred by the end of it.
The key to this problem is understanding what and how data context of a data template works. Whenever you define a Data Template for a View Model, the data context for the view that follows, whether it is a user control or just xaml itself, is the View Model! This shouldn't be a surprise to anyone.
But this will surprise people: if you specify a User Control, the Data Context of the User Control is not set during construction of the User Control! In other words, in the constructor of User Control, Data Context is going to be null. Furthermore, any XAML code that relies on the Data Context at construction time, which in this case was my FrameworkElement resource called ProxyElement got its DataContext set to null because it gets constructed at construction time of the User Control!
So when does the DataContext get set? Simply after the User Control is created. In pseudo code, this following describes the logic behind drawing a ViewModel:
Draw ViewModel x;
DataTemplate in ResourceDictionary says ViewModel x can be drawn using UserControl abc
Let's create a new instance of UserControl abc
Let's now assign the DataContext of abc to the ViewModel itself.
Let's return the newly created instance of UserControl abc
So what do we do to solve the problem in this question?
UserControl.xaml:
<UserControl ...
DataContextChanged="DaCoHasChanged">
<UserControl.Resources>
<FrameworkElement x:Key="ProxyElement" /> <!--Remove DataContext="{Binding}"-->
</UserControl.Resources>
<DataGrid ...>
<DataGridComboBoxColumn
ItemsSource="{Binding Path=DataContext.ProductCompanies,
Source={StaticSource ProxyElement}}"
... />
</DataGrid>
</UserControl>
UserControl.xaml.cs:
private void DaCoHasChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var proxyElement = Resources["ProxyElement"] as FrameworkElement;
proxyElement.DataContext = e.NewValue; // instead of e.NewValue, you could
// also say this.DataContext
}
I am trying to figure out a way of getting rid of the code in the code-behind file. But till then, if someone else hits this problem, then they might be able to get inspired from this solution.
Credit to the concept behind this solution goes to: How to set the DataContext for a View created in DataTemplate from ViewModel
Try this
<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding Products}">
<DataGridTemplateColumn Header="Company">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<ComboBox
ItemsSource="{Binding Path="{Binding DataContext.ProductCompanies,RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"
DisplayMemberPath="Name" SelectedValuePath="Id"
SelectedValueBinding="{Binding CompanyId}" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid.Columns>
</DataGrid>
Now as I got your problem I think the problem is in DataGridComboBoxColumn I dont know why it not Binding using RelativeResource . Try it with DataGridTemplateColumn and you would not require any ProxyElement I hope this will help.
I have a grid column defined. The parent grid gets its items from an ObservableCollection of type ItemClass. ItemClass has two properties: String Foo, and bool IsEditAllowed.
This column is bound to property Foo. There's a control template for editing the cell. I'd like to bind the ItemClass.IsEditAllowed property to the IsEnabled property of the TextBox in the template.
The question is how to bind it. Can this be done? The XAML below gets me "Cannot find source for binding with reference" in the debug trace.
The grid will let me bind the ItemClass itself to the field via some "custom" event thingy, and I can then bind to any of its properties. That's fine, but it seems kludgy. But if it's the only way, it's the only way.
<dxg:GridColumn
Header="Foo Column"
FieldName="Foo">
<dxg:GridColumn.EditTemplate>
<ControlTemplate>
<TextBox Text="{Binding Value, Mode=TwoWay}"
IsEnabled="{Binding Path=IsEditAllowed, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:ItemClass}, AncestorLevel=1}}" />
</ControlTemplate>
</dxg:GridColumn.EditTemplate>
</dxg:GridColumn>
There are two potentially easier ways to set up this binding.
Name the grid. Then your binding could look something like this (assuming dxg:GridControl has a property named "Items" and that you have assigned an instance of your ItemClass to that property):
<TextBox IsEnabled="{Binding Path=Items.IsEditAllowed, ElementName=MyGridControl} />
Use relative binding, but look for the GridControl rather than something nominally internal to the way GridControl works (that is, GridControlContentPresenter). This gets you away from the implementation details of GridControl, which are perhaps more likely to change in ways that break your application than are properties on GridControl itself.
<TextBox IsEnabled="{Binding Path=Items.IsEditAllowed, RelativeSource={RelativeSource AncestorType={x:Type dxg:GridControl}}}" />
You may also want to read up on the Visual Tree and the Logical Tree in WPF/xaml. The "Ancestor" in relative bindings refers to ancestors in the visual tree, that is, things like parent containers, and not to super- or base classes (as you've discovered, I think).
Here's the answer[1]. FindAncestor finds ancestors in the runtime XAML tree, not in arbitrary C# objects. It cannot walk up to the ItemClass instance from the member we're bound to. But we do know that somebody above us in the XAML tree bound us to that member, and he was bound to the ItemClass instance itself. So whoever that is, we find him, and then we've got the ItemClass.
So let's add debug tracing to the binding, and we'll see what the XAML situation looks like at runtime. No doubt there are other and probably smarter ways to do that, but I happen to know this one without any research.
First add this to the namespaces at the top of the XAML file:
xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase"
...and then to the binding itself, add this:
diag:PresentationTraceSources.TraceLevel=High
Like so:
<TextBox Text="{Binding Value, Mode=TwoWay}"
IsEnabled="{Binding Path=IsEditAllowed, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:ItemClass}, AncestorLevel=1}, diag:PresentationTraceSources.TraceLevel=High}"
/>
At runtime, when the TextEdit's IsEnabled property tries to get a value from the binding, the binding walks up through the XAML tree looking for an ancestor of the specified type. It keeps looking until it finds one or runs out of tree, and if we put tracing on it, it traces the type of everything it finds the whole way up. We've told it to look for garbage that it'll never find, so it will give us a trace of the type of every ancestor back to the root of the tree, leaf first and root last. I get 75 lines of ancestors in this case.
I did that, and found a few likely candidates. I checked each one, and the winner turned out to be dgx:GridCellContentPresenter, which has a RowData property. RowData has a lot of properties, and RowData.Row is the row's instance of ItemClass. dxg:GridCellContentPresenter belongs to the DevExpress grid library we're using; in another vendor's grid class, there would presumably be some equivalent.
Here's the working binding:
<TextBox Text="{Binding Value, Mode=TwoWay}"
IsEnabled="{Binding Path=RowData.Row.IsEditAllowed, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type dxg:GridCellContentPresenter}, AncestorLevel=1}}"
/>
If DevExpress, the vendor, rewrites their GridControl class, we'll be in trouble. But that was true anyhow.
...
[1] Better answer, though it's too DevExpress specific to be of any real interest: The DataContext of the TextBox itself turns out to be dxg:EditGridCellData, which has a RowData property just like GridCellContentPresenter does. I can just use IsEnabled="{Binding Path=RowData.Row.IsEditAllowed}".
However, what I really wanted to do all along was not to present a grid full of stupid disabled textboxes, but rather to enable editing on certain rows in the grid. And the DevExpress grid lets you do that through the ShowingEditor event.
XAML:
<dxg:GridControl Name="grdItems">
<dxg:GridControl.View>
<dxg:TableView
NavigationStyle="Cell"
AllowEditing="True"
ShowingEditor="grdItems_TableView_ShowingEditor"
/>
</dxg:GridControl.View>
<!-- ... Much XAML ... -->
</dxg:GridControl Name="grdItems">
.cs:
private void grdItems_TableView_ShowingEditor(object sender, ShowingEditorEventArgs e)
{
e.Cancel = !(e.Row as ItemClass).IsEditAllowed;
}
I have two controls within my UserControl where I bind to the exact same object using Element Binding:
AllowNext="{Binding ElementName=MainGrid, Path=DataContext.CanContinue}"
On the first control it works fine but on the second I get a binding exception:
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=MainGrid'. BindingExpression:Path=DataContext.CanContinue; DataItem=null; target element is 'WizardPage' (Name='DeductionPage'); target property is 'AllowNext' (type 'Boolean')
I have also tried using RelativeSource binding on the second control:
AllowNext="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Grid}}, Path=DataContext.CanContinue}"
But this also gives me an error.
Does anyone know what this might be?
--
Here is the simplified control:
<Grid Name="MainGrid">
<w:Wizard Name="MyWizard" w:Designer.PageIndex="1" DataContext="{Binding ElementName=MainGrid, Path=DataContext.Policy}" >
<w:WizardPage Header="Main Member" MaxHeight="600" AllowNext="{Binding ElementName=MainGrid, Path=DataContext.CanContinue}" Name="MainPage">
</w:WizardPage>
<w:WizardPage Name="DeductionPage" Header="Policy Details" AllowBack="False" AllowNext="{Binding ElementName=MainGrid, Path=DataContext.CanContinue}">
</w:WizardPage>
</w:Wizard>
</Grid>
Now as I mentioned, MainPage binds fine, whereas the DeductionPage does not bind at all and gets the supplied error. The DataContext of MainGrid is set from code behind:
public void SetDataContext(object o)
{
MainGrid.DataContext = o;
}
I bet it's the MainGrid which is the binding source is not in the logical tree of your binding target.
This is the problem absolutely with the binding element. However, you didn't give the source so You want to debug it and solve the issue.
Refer the below url and "Cannot find source for binding with reference" section where explained obviously how to debug and solve it.
http://www.codeproject.com/Articles/244107/Debugging-WPF-data-bindings
I'm using PRISM v2, CAL, SL4 and MVVM and have a delegate command on my ViewModel called CheckCommand. The ItemsControl contains a checkbox and I'm trying to get the items in ItemsControl/Checkbox to fire this command when it's checked - but it's not communication back to the viewmodel!
I think it's because each items 'datacontext' is the individual object the item is bound to, rather than the ViewModel?
- My suspicion is actually correct, cause if I move my DelegateCommand out of the viewmodel and into the class defining the items in itemscontrol I can see the commands/methods beeing fired!
View:
<ListBox x:Name="BasketListBox" ItemsSource="{Binding BasketCollection}" MinWidth="200">
<ListBox.ItemTemplate>
<DataTemplate>
<CheckBox commands:Checked.Command="{Binding CheckCommand}" IsChecked="False" </CheckBox>
</DataTemplate>
</ListBox.ItemTemplate>
Can anyone point me in the right direction please?
Cheers, Mcad.
EDIT 1:
The commanding now works, see solution below. BUT, I now run into another problem:
"An exception occurred while creating a region with name 'basketRegion'. The exception was: System.InvalidOperationException: ItemsControl's ItemsSource property is not empty. This control is being associated with a region, but the control is already bound to something else. If you did not explicitly set the control's ItemSource property, this exception may be caused by a change in the value of the inherited RegionManager attached property"
Created seperate question for this problem to make it more clean:
PRISM-MVVM, ItemsControl problem with View injection
You want every CheckBox to fire the same command? You could:
<CheckBox commands:Checked.Command="{Binding DataContext.CheckCommand, ElementName=BasketListBox}"
Or you could have every child view model expose the command via their own property.
Thanx Kent. You put me on the right path to solve this, ended up doing this:
<ListBox x:Name="basketListBox" ItemsSource="{Binding basketcollection}" MinWidth="200">
<ListBox.ItemTemplate>
<DataTemplate>
<CheckBox commands:Checked1.Command="{Binding DataContext.CheckCommand, ElementName=basketListBox}" Content="{Binding basketName}"> </CheckBox>
</DataTemplate>
</ListBox.ItemTemplate>