Declarative progress bar binding

Question

After binding the command of a button to an action, I call an object which exposes a progress event.

event System.EventHandler<ProgressChangedEventArgs> ProgressChanged

I would like to display that in my XAML in the best way.

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One way can be to expose two bindable fields in my VM

member x.Iteration with get()     = _iteration
                   and set(v:int) = _iteration <- v
                                    x.NotifyPropertyChanged <@this.Iteration@>

member x.IterationVisible with get()      = _iterationVisible
                          and set(v:bool) = _iterationVisible <- v
                                            x.NotifyPropertyChanged <@this.IterationVisible@>

then where I am called to perform the action I would just update the properties

member x.CompleteInference(algorithm:IGeneratedAlgorithm) =
    x.IterationVisible <- true
    algorithm.ProgressChanged.Add(fun args -> x.Iteration <- args.Iteration)
    algorithm.run()
    x.IterationVisible <- false

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That leads to 2 questions :

• Is there a direct way in F# to expose the progressChanged event, without going through this intermediate Iteration property, that can be processed by WPF ? Is it the most declarative we can get / do we always have to store some state somewhere ?

• Additionaly, is there a natural way to do this 'state machine' binding entirely in XAML ?

Answer 1

To my knowledge there is no way to handle events in xaml, so exposing the event changes through a property is probably the best you can do.

To achieve "'state machine' binding" in xaml, you could expose the progress as a size and then bind the width of your progress bar to that property. See here for an example of this.