How to access activity Argument within ActivityDesigner? - arguments

Question

I need to get my custom activity's InArgument value at ActivityDesigner.
MyActivity:
[Designer(typeof(ReadTextDesigner))]
public sealed class ReadText : CodeActivity
{
public InArgument<string> ImageName { get; set; }
protected override void Execute(CodeActivityContext context)
{
}
}
My designer:
public partial class ReadTextDesigner
{
public ReadTextDesigner()
{
InitializeComponent();
//this.ModelItem is null here.. WHY is it null?
//How do I get Activity's ImageName here?
}
}
I also have a button as in the image below and when you click on it, I CAN SET my custom Activity's value like this:
private void BtnStart_OnClick(object sender, RoutedEventArgs e)
{
this.ModelItem?.Properties["ImageName"]?.SetValue(new InArgument<string>()
{
Expression = "some value"
});
}
XAML:
<sapv:ExpressionTextBox
Expression="{Binding Path=ModelItem.ImageName, Mode=TwoWay, Converter={StaticResource ArgumentToExpressionConverter}, ConverterParameter=In }"
ExpressionType="s:String"
HintText="Enter a string"
OwnerActivity="{Binding Path=ModelItem}"
Width="110"
Margin="0,5"
Grid.Row="0"
MaxLines="1"
x:Name="TxtImagePath"/>
<Button Grid.Column="0" Grid.Row="1" Content="Get Image" HorizontalAlignment="Center" Click="BtnStart_OnClick" x:Name="BtnStart"/>
How do I GET Activity InArgument ReadTextDesigner constructor?

Answer 1

Its quite weird but I found a workaround. Although this is A solution, I'm hoping for a much better one;
Since within the constructor, I cannot get the ModelItem, I created a new Thread apart from the Main Thread. This new Thread waits 2 milliseconds and then tries to get ModelItem and it succeeds somehow.
Here is the new modified ReadTextDesigner code (Note: I only changed ReadTextDesigner code nothing else)
public ReadTextDesigner()
{
InitializeComponent();
new TaskFactory().StartNew(() => { this.Dispatcher.Invoke(() => SetImage(this)); });
}
private void SetImage(ReadTextDesigner designer)
{
Thread.Sleep(2);
if (designer.ModelItem.GetCurrentValue() is ReadText readText)
{
var imageName = readText.ImageName?.Expression?.Convert<string>();
if (!string.IsNullOrWhiteSpace(imageName))
{
//imageName has a value at this point!
}
}
}
ModelItem is not null anymore and carries the necessary value.
Hope this will help someone or someone post a better solution.
Cheers!