Question

I have a WPF project using CM. I have a progress bar that I would like to animate smoothly. I have a storyboard containing a DoubleAnimation. The problem is that when I try to bind the Duration of the DoubleAnimation to a property on my view model, I get a TargetInvocationException on running the program.

The XAML for the progress bar looks like this:

<ProgressBar Name="ProgressBar" Width="400" Height="18">
    <ProgressBar.Style>
        <Style>
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=IsMeasuring}" Value="True">
                    <DataTrigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation 
                                    Storyboard.Target="{Binding TemplatedParent}" 
                                    Storyboard.TargetProperty="Value" 
                                    From="0" 
                                    To="100" 
                                    Duration="{Binding MeasurementDuration}" 
                                />
                            </Storyboard>
                        </BeginStoryboard>
                    </DataTrigger.EnterActions>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ProgressBar.Style>
</ProgressBar>

While the property in my view model looks like this:

private Duration measurementDuration = new Duration(TimeSpan.FromSeconds(1));
public Duration MeasurementDuration
{
    get { return measurementDuration; }
    private set
    {
        measurementDuration = value;
        NotifyOfPropertyChange(() => MeasurementDuration);
    }
} 

I feel that the answer is staring straight at me, but I simply cannot find it. Thanks in advance for any help.

Answer 1

as far as i know, a binding to an animation in this implementation way as yours throws always an error.
In the case to change properties of an Timeline-Object while it is animated, you have to use the methods <StoryboardName>.Begin() to create a new clock for the Storyboard and <StoryboardName>.Seek() to jump to the reached duration.

Before you call the <name>.Begin() method, you change your desired properties and it should work.

Their exists a example in the msdn:
http://archive.msdn.microsoft.com/Project/Download/FileDownload.aspx?ProjectName=wpfsamples&DownloadId=7734

In fact, that in the msdn example “only” the KeyFrames-objects of a an TimeLine-Object will be changed, you have to call the Storyboard.Stop() method before you change the Duration-property.

Try it and maybe it helps 🙂

Kind regards
Sb