Strange exception message showing a property name only

GoXam
1

Hello Walter

I have a NodeData class with a property called Icon, and a property called Status. The icon has a private setter and a public getter and is automatically set when the property Status gets set.

public class MyNodeData : GraphLinksModelNodeData<string> {
    private PartStatus _status;
    public PartStatus Status {
        get { return this._status; }
        set {
            PartStatus oldStatus = this._status;
            this._status = value;
            this.IconName = this.IconName; // changes the icon depending on status
            RaisePropertyChanged("Status", oldStatus, value);
        }
    }

    private string _iconName;
    public string IconName {
        get { return this._iconName; }
        set {
            // grabs icon from cache depending on status, which is not interesting here
            BitmapImage icon = ...

            BitmapImage oldIcon = this.Icon;
            this.Icon = icon;
            RaisePropertyChanged("Icon", oldIcon, icon);
            this._iconName = value;
        }
    }

    public BitmapImage Icon { get; private set; }

    // various other properties
    ...
}

with PartStatus being the following enum:

public enum PartStatus {
    Default,
    Selected,
    Unselectable,
    Disabled
}

The xaml looks like this:

<Style x:Key="StatusStackPanelStyle" TargetType="StackPanel">
    <Style.Triggers>
        <DataTrigger Binding="{Binding Path=Data.Status}" Value="{x:Static style:PartStatus.Default}">
            <Setter Property="go:Part.Selectable" Value="{Binding Path=Data.IsSelectable}" />
        </DataTrigger>
        <DataTrigger Binding="{Binding Path=Data.Status}" Value="{x:Static style:PartStatus.Selected}">
            <Setter Property="go:Part.Selectable" Value="{Binding Path=Data.IsSelectable}" />
        </DataTrigger>
        <DataTrigger Binding="{Binding Path=Data.Status}" Value="{x:Static style:PartStatus.Disabled}">
            <Setter Property="go:Part.Selectable" Value="False" />
        </DataTrigger>
        <DataTrigger Binding="{Binding Path=Data.Status}" Value="{x:Static style:PartStatus.Unselectable}">
            <Setter Property="go:Part.Selectable" Value="False" />
        </DataTrigger>
    </Style.Triggers>
</Style>

<!-- I am leaving out all attributes of no interest as there are quite a lot -->
<DataTemplate x:Key="MyNodeTemplate">
    <StackPanel Style="{StaticResource StatusStackPanelStyle}">
        <go:SpotPanel>
            <go:NodePanel>
                <StackPanel>
                    <!-- this grid exists so an image can be displayed UniformToFill and at the same time be centered -->
                    <Grid>
                        <Image Source={Binding Path=Data.Icon} />
                    </Grid>
                </StackPanel>
            </go:NodePanel>
            <!-- just like the StatusStackPanelStyle, this style sets Stroke, LinkableFrom/To and Cursor based on the Node's status -->
            <Ellipse Style="{StaticResource StatusPortStyle}" />
            <!-- there are many more Ports, which only differ in position --->
        </go:SpotPanel>
        <TextBlock Text="{Binding Path=Data.Text}" />
        <!-- some more elements to show additional information -->
    </StackPanel>
</DataTemplate>

When I select a node in the diagram, its Status gets set to PartStatus.Selected obviously. When I try to draw a link but cancel the operation, an InvalidOperationException gets thrown, which shows nothing but “Icon” as error message but only if there was a change in Status recently. The linking operation itself does not change the Status. Checking the stack trace and overriding the ChangeDataValue function of GraphLinksModel showed me that the GraphLinksModel tries to reset the changed properties of the node, which in case of the Icon property is invalid of course due to the private setter. I solved this by checking for the property name for “Icon” in the function ChangeDataValue before calling the base function but the question is, as the incorrect linking operation doesn’t change the node’s Status and the Status change happened beforehand and has nothing to do with the linking operation, why is it actually trying to revert these properties?

2

I’m unsure of what is happening in your app.

But your property setters are clearly incorrect, because RaisePropertyChanged is called even if the new value has not changed. It is essential that there not be any change notification unless there really was a meaningful state change.

So I suggest that you review and fix all of your property setters, and then see if the problem still happens.

3

That would not change a thing, because the tool is actually trying to reset the Status from Default to Selected or vice versa, so there is indeed a change identified and tried to undo. But there shouldn’t be one, as the selection happened beforehand and has nothing to do with drawing the link.

4

Have you fixed the property setters to be sure that that wasn’t the cause of the error?