How do I serialise Lambdas and Event delegates when Tombstoning on the Windows Phone 7?

Question

I've been using the Game State Management sample which has worked so far. I've hit a snag though: when Tombstoning, the screens are serialised; the only trouble is, the MessageBoxScreen has event handlers for Accepted and Cancelled.

What's the best way to serialise these? I did a bit of research on using Expression Trees but this seemed overly complex for what I wanted to do.

How do you serialise these? Or... What alternative approach do you use to save the state of a screen that contains delegates?

Cheezmeister · Answer 1 · 2011-02-09T03:38:05.743

1

I'd definitely steer clear of attempting to serialize anything remotely resembling a lambda, or for that matter, named methods. Remember: you're storing state, and nothing else.

Depending on how far and wide your various assignments to these delegates are, you might be able to get away with maintaining a Dictionary<String, WhateverDelagateType>, serializing the keys and looking up the callbacks after deserialization.

Another thing to consider--I'm no expert, but reading between the lines it sounds as if you're working towards tombstoning a very temporary modal dialog. Do you really want that? You might be better off bringing your user right to the high scores table, or whatever follows your dialog, on his/her return.

edited Feb 09 '11 at 03:38

answered Feb 07 '11 at 01:17

Cheezmeister

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Thanks. The screen is part of the Game State Management sample. The sample didn't demonstrate the use of this screen though, presumably because of the complications around serialising labmdas and delegates (it has 2 events, Accepted and Cancelled). I modified it to pass in a lambda (e.g. new MessabeBoxScreen(@"Game over!", ()=>showHighScoreScreen ) ) The lambda is called when the user clicks the back button or it times out. This was certainly handy, at least 'till I started work on the task 'Get Tombstoning working' ! :| – Steve Dunn Feb 07 '11 at 07:49
Well, it sounds like you're in control, so I've updated my answer accordingly. Lambdas are fun, but in this case I think you're gonna have to factor it out into a real method. HTH – Cheezmeister Feb 09 '11 at 03:33

score 1 · Accepted Answer · answered Feb 24 '11 at 11:34

I decided against this. I instead persists game flow as a kind of 'flow chart'.

The flow chart is declared in code and has properties 'LastShape' and 'LastResultFromShape'.

In my code, I rebuild the flow chart definitions each time, something like this:

flowChart.AddShape( "ShowSplash" );
flowChart.AddLine( "MainMenu", ()=>lastResult=="Clicked" || lastResult=="TimedOut");

flowChart.AddShape( "MainMenu");
flowChart.AddLine( @"ShowOptions", ()=>lastResult=="OptionsClicked");
flowChar.AddLine( @"ShowSplash", ()=>lastResult==@"TimedOut");

etc.etc.

The flow goes from the top down, so 'AddLine' relates to the last shape added.

After tombstoning, I just read the last shape and the last result and decide where to go in the flowchart based on that.

How do I serialise Lambdas and Event delegates when Tombstoning on the Windows Phone 7?

2 Answers2