Crash in "hf learns secret"-type events when the teacher ID is not set

[MatthiasValvekens]

This was the event that caused the problem:

    <historical_event>
        <id>26699</id>
        <year>125</year>
        <seconds72>22995</seconds72>
        <type>hf learns secret</type>
        <student_hfid>4018</student_hfid>
        <teacher_hfid>-1</teacher_hfid>
        <artifact_id>54</artifact_id>
        <interaction>SECRET_1</interaction>
    </historical_event>

The HF in question is my adventurer, who learned the secrets of life and death by reading a tome. Hence, there's no teacher involved as such. I got a NullReferenceException on the LegendsViewer.Legends.HFLearnsSecret.Print call when I tried to view my adventurer's summary page in LegendsViewer.

Changing the teacher_hfid to match the student's fixed the issue, though, but there's probably some code assuming that a teacher id is always set to some sensible value.

I don't have a working C# build environment at hand right now, but I'll try and track down the piece of code responsible for the crash.

[JyeGuru]

Legends-Viewer/LegendsViewer/Legends/Events.cs

Line 1234 in a00e70b

case "teacher_hfid": Teacher = world.GetHistoricalFigure(Convert.ToInt32(property.Value)); break;

case "teacher_hfid": Teacher = world.GetHistoricalFigure(Convert.ToInt32(property.Value)); break;

world.GetHistoricalFigure() returns null if passed -1

[MatthiasValvekens]

Hmm, the plot thickens. I restored my "broken" legends file, and tried searching for another HF who learned a secret from an artifact (and has teacher_hfid set to -1). For some reason, this worked fine. Could it be that the HFLearnSecret object itself somehow fails to be created? LegendsViewer.Legends.HFLearnsSecret.Print is the top entry in the NullReferenceException's stack trace, anyway. I suppose that means that the .Print call failed because its underlying object reference wasn't set.

Full stack trace for good measure:

System.NullReferenceException: Object reference not set to an instance of an object.
   at LegendsViewer.Legends.HFLearnsSecret.Print(Boolean link, DwarfObject pov)
   at LegendsViewer.Controls.HistoricalFigureHTMLPrinter.PrintEvents()
   at LegendsViewer.Controls.HistoricalFigureHTMLPrinter.Print()
   at LegendsViewer.Controls.HTMLControl.GetControl()
   at LegendsViewer.DwarfTabPage.LoadPageControl()
   at LegendsViewer.DwarfTabPage.NewPageControl(PageControl pageControl)
   at LegendsViewer.DwarfTabControl.Navigate(ControlOption control, Object navigateObject)
   at LegendsViewer.frmLegendsViewer.listSearch_SelectedIndexChanged(Object sender, EventArgs e)
   at System.Windows.Forms.ListBox.WmReflectCommand(Message& m)
   at System.Windows.Forms.ListBox.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

The (working) histfig's event:

    <historical_event>
        <id>5977</id>
        <year>53</year>
        <seconds72>252000</seconds72>
        <type>hf learns secret</type>
        <student_hfid>554</student_hfid>
        <teacher_hfid>-1</teacher_hfid>
        <artifact_id>2</artifact_id>
        <interaction>SECRET_1</interaction>
    </historical_event>

EDIT: upon closer inspection, the code that does the artifact parsing might be failing here. I got this when trying to view the tower I found the book at:

System.NullReferenceException: Object reference not set to an instance of an object.
   at LegendsViewer.Legends.ArtifactCreated.Print(Boolean link, DwarfObject pov)
   at LegendsViewer.Controls.SitePrinter.Print()
   at LegendsViewer.Controls.HTMLControl.GetControl()
   at LegendsViewer.DwarfTabPage.LoadPageControl()
   at LegendsViewer.DwarfTabPage.NewPageControl(PageControl pageControl)
   at LegendsViewer.DwarfTabControl.Navigate(ControlOption control, Object navigateObject)
   at LegendsViewer.frmLegendsViewer.listSearch_SelectedIndexChanged(Object sender, EventArgs e)
   at System.Windows.Forms.ListBox.WmReflectCommand(Message& m)
   at System.Windows.Forms.ListBox.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

EDIT 2: I found the root cause. Artifact ID 54 refers to a book that doesn't exist in the legends XML, so it's probably a bug in DF, not in Legends Viewer.

    <artifact>
        <id>53</id>
        <name>the tower is my life</name>
        <item>the tower is my life</item>
    </artifact>
    <artifact>
        <id>55</id>
        <name>uncanny book</name>
        <item>uncanny book</item>
    </artifact>

Still, it's probably worth replacing the artifact name by something like UNKNOWN_ARTIFACT, to prevent an exception from being raised.

[JyeGuru]

I'll update my local copy of the source and see about reproducing this weekend. Can you pass your export file? (Dropbox link/etc)

[MatthiasValvekens]

Here's a google drive link:
https://drive.google.com/file/d/0B3D_3d9BMj8NanlmTlRGYUFGTWc/view?usp=sharing

(file generated on DF 0.40.23, by the way)

[JyeGuru]

Artifact ID 54 refers to a book that doesn't exist in the legends XML

That'd do it.

[JyeGuru]

https://github.com/Parker147/Legends-Viewer/blob/master/LegendsViewer/Legends/Events.cs#L1252

            if (Teacher != null)
                eventString += Teacher.ToLink(link, pov) + " taught " + Student.ToLink(link, pov) + " (" + Interaction + ")";
            else 
                eventString += Student.ToLink(link, pov) + " learned (" + Interaction + ") from " + Artifact.ToLink(link, pov);

It appears to check for teacher being null, but not the artifact.