How to make an InArgument's value dependant upon the value of another InArgument at design time

I have a requirement to allow a user to specify the value of an InArgument / property from a list of valid values (e.g. a combobox). The list of valid values is determined by the value of another InArgument (the value of which will be set by an expression).

For instance, at design time:

• User enters a file path into workflow variable FilePa开发者_JAVA技巧th
• The DependedUpon InArgument is set to the value of FilePath
• The file is queried and a list of valid values is displayed to the user to select the appropriate value (presumably via a custom PropertyValueEditor).

Is this possible?

Considering this is being done at design time, I'd strongly suggest you provide for all this logic within the designer, rather than in the Activity itself.

Design-time logic shouldn't be contained within your Activity. Your Activity should be able to run independent of any designer. Think about it this way...

You sit down and design your workflow using Activities and their designers. Once done, you install/xcopy the workflows to a server somewhere else. When the server loads that Activity prior to executing it, what happens when your design logic executes in CacheMetadata? Either it is skipped using some heuristic to determine that you are not running in design time, or you include extra logic to skip this code when it is unable to locate that file. Either way, why is a server executing this design time code? The answer is that it shouldn't be executing it; that code belongs with the designers.

This is why, if you look at the framework, you'll see that Activities and their designers exist in different assemblies. Your code should be the same way--design-centric code should be delivered in separate assemblies from your Activities, so that you may deliver both to designers, and only the Activity assemblies to your application servers.

When do you want to validate this, at design time or run time?

Design time is limited because the user can use an expression that depends on another variable and you can't read the value from there at design time. You can however look at the expression and possibly deduce an invalid combination that way. In this case you need to add code to the CacheMetadata function.

At run time you can get the actual values and validate them in the Execute function.