How to configure ExpressionTextBox bindings / OwnerActivity when used in a dialog? - workflow-foundation-4

Question

Our group is working on a Custom Activity Designer around our Email activity. It's a pretty straight forward designer, allow the user to enter settings / creds, but instead of cluttering the activity designer with all the settable options, we thought about putting some settings in a dialog window. (Which opens when you click the button beside the server address box).
Some of our email activity properties are InArguments so we are trying to make use of the ExpressionTextBox to display these values without much luck. The main problem is we aren't sure how to properly set up the binding and the OwnerActivity on the ExpressionTextBox. In the Activity Designer's xaml this is simply done by setting Expression=ModelItem.Property using a converter for the InArgument and setting the OwnerActivity=ModelItem, like this:
<view:ExpressionTextBox HintText="Enter a VB Expression" Expression="{Binding ModelItem.ServerAddress, ConverterParameter=In, Converter={StaticResource ArgumentToExpressionConverter}, Mode=TwoWay}" ExpressionType="{x:Type system:String}" OwnerActivity="{Binding ModelItem}" Margin="2" MaxLines="1" />
If anyone has any ideas on how we could accomplish this in a dialog, please advise.

Answer 1

Well, this is more a WPF\MVVM question than WF4, really.
When developing custom activities designers you just have to keep one thing in mind: any change made on designer\dialog should be reflected on ModelItem. Either through XAML binding expressions or through code on ModelItem.Properties property.
Now, when and how you do it, there are several answers to that but that's really an implementation detail and depends on how you want to do it.
Lets assume you're showing the dialog on button-beside-the-server-address-box click. And lets also assume you've access to dialog textboxes through their name. At that point, you've access to ModelItem so just set its properties as needed:
private void ButtonNextToServerAddressBox_OnClick(object sender, RoutedEventArgs e)
{
var dialog = new ServerAddressEditor();
var result = dialog.ShowDialog();
if (result ?? false)
{
ModelItem.Properties["Server"].SetValue(new InArgument<string>(dialog.ServerTextBox.Text));
ModelItem.Properties["Port"].SetValue(new InArgument<string>(dialog.PortTextBox.Text));
// ... set all other properties
}
}
Now, if you are using any other pattern, or you want pure MVVM, it can be a little more tricky because of how ModelItem works. But this is a totally fine approach.

Answer 2

I resolved this by creating a property in the dialog's ViewModel to hold the Activity Designer's ModelItem.
public ModelItem OwnerActivity {
get { return _OwnerActivity; }
set { _OwnerActivity = value; }
}
vm.OwnerActivity = this.DataContext.ModelItem;
I then set the Xaml for the Expression Text Box in my dialog to binding to this:
<view:ExpressionTextBox HintText="Enter a VB Expression" Expression="
{Binding Path=OwnerActivity.ServerAddress, ConverterParameter=In, Converter=
{StaticResource ArgumentToExpressionConverter}, Mode=TwoWay}" ExpressionType="
{x:Type system:String}" OwnerActivity="{Binding OwnerActivity}" Margin="2"
MaxLines="1" />
Because I'm now binding directly to the ModelItem from the Activity Designer, any change made to the ModelItem property from the dialog is ALWAYS committed, even if you choose to Cancel from the dialog. To wire up the Ok/Cancel buttons so they work accordingly, I did the following in the dialog:
// declare a ModelEditingScope to make changes transactional
private ModelEditingScope _editScope;
// add this to the constructor of the dialog to begin transactional edits on the ModelItem
_editScope = editorViewModel.OwnerActivity.BeginEdit();
// ok & cancel button click event to commit or revert the changes.
private void OK_Click(object sender, RoutedEventArgs e)
{
_editScope.Complete();
this.DialogResult = DialogResult.OK;
this.Close();
}
private void Cancel_Click(object sender, RoutedEventArgs e)
{
_editScope.Revert();
this.DialogResult = DialogResult.Cancel;
this.Close()
}