Develop Reference

Why is my DataContext getting switched out from under me for a binding?

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}"/>

Custom control binding is not updating

I'm having trouble getting my binding to work correctly. Basically I have this, call this Control1.xaml. The commented out portion of the code binds correctly and updates as expected.
<progControls:CalibrationSummary
</progControls:CalibrationSummary>
<!--<TextBlock Text="{Binding Path=NumberOfCalibrations, Mode=OneWay}"/>-->
However, if I put that commented code in a custom control called CalibrationsSummary.xaml, I cannot bind this to NumberOfCalibrations.
Here's what CalibrationsSummary looks like
<Grid>
<TextBlock Text="{Binding Path=NumberOfCalibrations, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}"/>
</Grid>
Note that I do use RelativeSource to try to get the property associated with Control1.xaml, tried TemplateBinding also. What am I doing wrong?

CalibrationSummary has no TemplatedParent unless you have put it in a ControlTemplate.
If you don't explicitly set the DataContext of the property of CalibrationSummary somewhere, it will inherit the DataContext from its parent control (which I assume is Control1) and then you can bind any property of this control's DataContext as usual without specifying any source:
<Grid>
<TextBlock Text="{Binding Path=NumberOfCalibrations}"/>
</Grid>

Forcing a ListBox to re-render

Background:
I have a ListBox containing items defined by DataTemplates. Right now, if an object in the list has the property IsEditable set to true, the item's property information will be displayed inside of textboxes (via DataTemplate change), instead of textblocks (so the user can edit the content of that list item)
IsEditable is toggled on/off by a button inside of each list item. I have been told that we need to keep the state of all objects consistent, which means I can't just rebind the ItemsSource and lose everything.
Currently, I'm using this to re-render:
this.lbPoints.Dispatcher.Invoke(DispatcherPriority.Render, new Action(() => { }));
Question:
The aforementioned code snippet KIND OF does its job. By "kind of", I mean, it does eventually cause my data to become re-rendered, but only when I scroll to the bottom of the list and then scroll back up to the item i'm trying to re-render.
1) How can I re-render the data immediately without having to scroll around to get it to show up?

The guys commenting are right that you're going about this the wrong way... there is rarely a need to force a ListBox to re-render. You're probably causing yourself some additional grief trying to switch the DataTemplates (although it is possible). Instead of that, think about data binding the TextBox.IsReadOnly property to your IsEditable property:
<TextBox IsReadOnly="{Binding IsEditable}" Text="{Binding Text}" />
Another alternative is to use a BooleanToVisibilityConverter to show a different Grid in your DataTemplate when your IsEditable property is true. Unfortunately, that Converter doesn't have an inverse operation, so you could create an IsNotEditing property to bind to the Grid in the DataTemplate that is originally displayed. I'm not sure if that's clear... see this example:
<DataTemplate DataType="{x:Type YourPrefix:YourDataType}">
<Grid>
<Grid Visibility="{Binding IsNotEditing, Converter={StaticResource
BooleanToVisibilityConverter}}">
<!-- Define your uneditable UI here -->
</Grid>
<Grid Visibility="{Binding IsEditing, Converter={StaticResource
BooleanToVisibilityConverter}}">
<!-- Define your editable UI here -->
</Grid>
</Grid>
</DataTemplate>
You could also define your own BooleanToVisibilityConverter class that has an IsInverted property, so that you can just use the one IsEditing property. You'd need to declare two Converters still, like this:
<Converters:BoolToVisibilityConverter x:Key="BoolToVisibilityConverter" />
<Converters:BoolToVisibilityConverter x:Key="InvertedBoolToVisibilityConverter"
IsInverted="True" />
Then your XAML would be like this:
<Grid Visibility="{Binding IsEditing, Converter={StaticResource
InvertedBoolToVisibilityConverter}}">
<!-- Define your uneditable UI here -->
</Grid>
<Grid Visibility="{Binding IsEditing, Converter={StaticResource
BoolToVisibilityConverter}}">
<!-- Define your editable UI here -->
</Grid>

WPF Bind to element in parent window

I'm trying to bind element's property in a child control to an element's property ina parent window, it doesn't work..
Here is png of what I'm trying to do:
Here is the xaml that doesn't work:
CurrentDate="{Binding ElementName=TimeBar, Path=SelectionStart,RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}"
Thanks.

create a dependency property in your usercontrol and then bind to it in your window
something like that: DependencyProperty implementations you can find all around here on stackoverflow
<YourUsercontrol x:Name="uc">
<YourSomeControl CurrentDate="{Binding ElementName=uc, Path=MyDp}"/>
</YourUsercontrol>
xaml window
<Window>
<ElementInParent x:Name="eip" />
<YourUsercontrol MyDp="{Binding ElementName=eip, Path=PropertyFromElementInParent}"/>

based on the following Answer LINK the SelectionStart is not a Bindable Probperty by default so you need to create a attached behavior or something similar

Binding ElementName along with Relative Source is not correct approach.
Besides the UserControl does not know the ElementName of the Parent since the two are in different XAML.
One approach is to set the data context of user control with the element name you want to bind it to and then use normal binding Path.
As shown in the example below:
In main window, we have a textbox and a user control.
We are setting data context of the user control with the text box.
In the user control, we are binding the Text property of the DataContext (which is essentially TextBox of main window).
<Window
xmlns:self="clr-namespace:experiments"
>
<StackPanel>
<TextBox x:Name="Name" Width="100"/>
<self:UserControl1 DataContext="{Binding ElementName=Name}"/>
</StackPanel>
</Window>
<UserControl x:Class="experiments.UserControl1">
<Grid>
<TextBlock Text="{Binding Path=Text}" Width="100" Background="AliceBlue" Height="50"/>
</Grid>
</UserControl>

Binding IsEnabled to the parent ViewModel instead of the UserControl ViewModel

I developed a user control in SilverLight that contains several child controls. Textboxes, ComboBoxes and so on.
The problem is, when I include that UserControl into a parent view and set the complete control to IsEnabled=False, the child controls in that specific UserControl are still enabled.
After all I found the problem.
Adding something like that, implies that the IsEnabled Binding is located in the UserControl binding, not as expected from myself in the DataContext of the parent.
<localControls:TeamEmployeeSelector Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2"
IsEnabled="{Binding CanModify}" DataContext="{Binding Confidentiality}"/>
QUESTION:
But there's still the question how I can bind the IsEnabled to the ViewModel of the Parent? Because it's not very elegant to copy the CanModify Property to the ViewModel of the Child Control.

Instead of modifying a binding in some way (for example you can make it dependent on other control name as it is proposed in other answer) I would move separate the control which will be disabled and control where DataContext will be changed. For example:
<ContentControl IsEnabled="{Binding CanModify}" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2">
<localControls:TeamEmployeeSelector DataContext="{Binding Confidentiality}"/>
</ContentControl>

Here is how I would do this.
Your TeamEmployeeSelector UserControl will contain a single root level element which by default is a Grid and is given the name "LayoutRoot".
Now you can bind the IsEnabled property of all the child elements to the UserControl like this:-
<TextBox IsEnabled="{Binding Parent.IsEnabled, ElementName=LayoutRoot}" ... />
By using element-to-element binding you do not need to copy the CanModify property in to child view models.
Some might suggest that you simply add an x:Name to your UserControl element and then bind directly to it rather than going via the Parent property of the root element as I do above. That'll work ok in Silverlight 4 but not in 3 or WP7. Personally I prefer the above.

This is a scoping issue. Generally, when creating a UserControl, you want to set itself as the DataContext for its sub-elements. This is most easily accomplished in the constructor:
UserControlExample() {
InitializeComponent();
RootElement.DataContext = this;
}
Where RootElement is the name you give to this first child (usually a Grid or panel) of your UserControl.
From here you can set natural bindings for your sub-elements like so:
<TextBox x:Name="MainTextBox" IsEnabled={Binding IsEnabled} />
This works, since TextBox inherits the DataContext of the parent layout panel.
Finally, if you want to have your UserControl's IsEnabled property to be related to its parent, this is best done at the point of declaration:
<Grid>
<UserControlExample IsEnabled={Binding CanModify} />
</Grid>
This way you keep your concerns separate. The sub-controls don't care what the UserControl is reflecting. They just need to know how to enable/disable when the control's IsEnabled property flips.
sub-controls IsEnabled bound to --> (UserControlExample is DataContext)
UserControlExample.IsEnabled bound to --> (VM is DataContext)
VM.CanModify

I don't know if it's possible in Silverlight, but in WPF I would use RelativeSource.
Have a look here.
Hope this help !

<localControls:TeamEmployeeSelector Grid.Row="1" Grid.Column="0"
Grid.ColumnSpan="2" IsEnabled="{Binding ElementName=SomeElementName_With_Parent_ViewModel, Path=DataContext.CanModify}" DataContext="{Binding Confidentiality}"/>