JSON.NET Line serialization winrt

Question

I'm having some trouble with serializing a ObservableCollection of Lines (Shape). I'm developing for Windows RT and I'm using JSON.NET v5.02. I'm getting the following exception for the code below:

ObservableCollection<Line> lines;
//some code
string linesString = JsonConvert.SerializeObjectAsync(lines); // problem

An exception of type Newtonsoft.Json.JsonSerializationException occurred in mscorlib.dll but was not handled in user code

Additional information: Error getting value from 'X1' on 'Windows.UI.Xaml.Shapes.Line'.

If there is a handler for this exception, the program may be safely continued.

Is this a bug and is there a possible workaround?

a sample project can be downloaded at the following link: http://speedy.sh/ByHWx/JsonNetProblem.rar — w.donk, Apr 11 '13 at 09:12

score 2 · Accepted Answer · answered Apr 11 '13 at 09:29

Your problem is a cross thread problem. When using await JsonConvert.SerializeObjectAsync(lines); that function will be executed in another thread (not the UI thread). Since a Windows.UI.Xaml.Shapes.Line is a UIElement and was created in the UI (main) thread you can't access the properties of the object in another thread. The solution would be to convert it to a simpler object that doesn't have this restrictions.

Besides, a Windows.UI.Xaml.Shapes.Line contains a lot of information, Visibility, IsEnabled etc, I think you would only need the X1, X2, Y1 and Y2. So you could just use this:

string s = await JsonConvert.SerializeObjectAsync(lines
             .Select(l => new 
                     {
                         l.X1,
                         l.X2,
                         l.Y1,
                         l.Y2
                     }).ToArray());

In this way, you get the properties you need in your UI (main) thread. Then pass that array to the serialize function. This way it works.

string s would now contain:

[{"X1":20.0,"X2":20.0,"Y1":40.0,"Y2":40.0},{"X1":20.0,"X2":20.0,"Y1":40.0,"Y2":40.0},{"X1":20.0,"X2":20.0,"Y1":40.0,"Y2":40.0},{"X1":20.0,"X2":20.0,"Y1":40.0,"Y2":40.0}]

Don't forget to use the `.ToArray()` if you don't you create a statemachine with the `.Select` A statemachine will be executed when it is needed, that is in the `SerializeObjectAsync` which is in another thread. By calling `.ToArray()` you force the statemachine to run and create an array in the UI thread. — SynerCoder, Apr 11 '13 at 09:41
Hi@SynerCoder Can I use your solution for my problem please let me know thanks in advance...http://stackoverflow.com/questions/17105051/save-information-of-line-and-images — Mohit, Jun 14 '13 at 10:05

score 0 · Answer 2 · answered Apr 11 '13 at 09:27

I am not sure whether Json.Net allow serializing framework class object. I tried with this.

public class CustomLine
{
    public double X1 { get; set; }
    public double X2 { get; set; }
    public double Y1 { get; set; }
    public double Y2 { get; set; }
}

I Changed the Line to CustomLine line. If you want to use Line class then retrieve properties X1, X2, Y1, Y2 and then assign it to CustomLine class properties.

JSON.NET Line serialization winrt

2 Answers2

Linked