"IsAsync" has no effect for slow property?

Question

I have a slow data source, so I create it asynchronously. Also, many properties of my viewmodel are themselves slow. Hence, I make them asynchronous too (binding to a Telerik property grid):

<Grid>
  <Grid.DataContext>
    <ObjectDataProvider ObjectType="{x:Type viewModels:MyViewModel}"
      IsAsynchronous="True" x:Name="myViewModel" />
  </Grid.DataContext>
  <telerik:RadPropertyGrid x:Name="settings" Item="{Binding IsAsync=True}">
    <telerik:RadPropertyGrid.PropertyDefinitions>
      <telerik:PropertyDefinition
        Binding="{Binding Path=SlowProperty,IsAsync=True,Mode=TwoWay}" />
    </telerik:RadPropertyGrid.PropertyDefinitions>
  </telerik:RadPropertyGrid>
</Grid>

When debugging, I can see that the data source is indeed created in another thread, hence not blocking the UI. However, when I get into SlowProperty the debugger reveals that I'm still in the Main Thread - which is proven by the fact that the UI hangs until the property returns.

Q: What am I missing here? Isn't IsAsync sufficient for asynchronous properties?

Edit: It seems this works for a normal TextBlock. Is the IsAsync behavior dependent on the implementation of a control? (In this case I suspect a bug in the property grid.)

Answer 1

You are always ecouraged to use IsAsync Binding with PriorityBinding. GUI will wait until property is executed. But with PriorityBinding it will check if the first Binding property is slow, if so, it will select the next placeholder binding (which should be fast). But when the slow property is evaluated, it would become the active value by the binding.

<TextBlock>
 <TextBlock.Text>
  <PriorityBinding FallbackValue="defaultvalue">
    <Binding Path="SlowestProp" IsAsync="True"/>
    <Binding Path="SlowerProp" IsAsync="True"/>
    <Binding Path="SurelyFastProp" />
  </PriorityBinding>
 </TextBlock.Text>
</TextBlock>    

In your case, you can simply set some defaultValue instead of giving multiple bindings.