Why can't I serialize an object with a struct in it?

Question

I have an "options" object that I'm trying to save to Settings

public class MainWindow
{
    public MyOptions MyOptions => (MyOptions)DataContext;

    public MainWindow()
    {
        InitializeComponent();

        DataContext = Settings.Default.MyOptions ?? new MyOptions();
    }

    private void OnOptionsChanged(object sender, PropertyChangedEventArgs e)
    {
        Settings.Default.MyOptions = MyOptions;
        Settings.Default.Save();
    }

    // etc.
}

MyOptions contains (among other things) a struct-value

public class MyOptions
{
    private MyStruct _myStruct;

    public MyOptions()
    {
        _myStruct = someDefaultValue;
    }

    // etc.
}

MyStruct contains only a single int:

public struct MyStruct
{
    private readonly int _someValue;
    public MyStruct(int someValue)
    {
        _someValue = someValue;
    }

    // etc.
}

When I make the call to Settings.Default.MyOptions = MyOptions;, all the values are set correctly, including myStruct.

However, when I restart the program and load the options with DataContext = Settings.Default.MyOptions, all the values are correctly loaded except for _myStruct, which defaults to 0!

According to everything I've read, this code should work. I've tried adding the [Serializable] attribute to both the class/struct, as well as implementing ISerializable (which I shouldn't have to do), but neither helped. What am I missing?

My first guess would be that it's not `struct` that's the problem, it's `readonly`. Deserialisation works by creating an instance of an object and then setting its fields. I can imagine why that wouldn't work with `readonly` fields. But this is completely untested guesswork. — , Dec 27 '16 at 20:38
Have you tried make someValue public, and make constructor parameterless? — gabba, Dec 27 '16 at 20:39

score 2 · Answer 1 · edited May 23 '17 at 12:24

2

Settings are serialized as XML, which has a limitation of excluding readonly members.

Removing readonly qualifier should fix this problem:

public struct MyStruct {
    internal int _someValue;
    public MyStruct(int someValue) {
        _someValue = someValue;
    }
}

edited May 23 '17 at 12:24

Community

1
1

answered Dec 27 '16 at 20:44

Sergey Kalinichenko

714,442
84
1,110
1,523

1

I removed the `readonly` but it's still not working. What other restrictions could be causing this? – BlueRaja - Danny Pflughoeft Dec 27 '16 at 21:04

score 1 · Accepted Answer · answered Dec 27 '16 at 21:07

1

Try this struct, in my test case it serialized right way:

public struct MyStruct
{
    public int SomeValue { get; set; }
}

answered Dec 27 '16 at 21:07

gabba

2,815
2
27
48

So `private` values can be serialized in classes but not structs? Is this documented anywhere? EDIT: I believe my question is answered [here](http://stackoverflow.com/questions/445915/deep-xml-serialize-a-struct-options). It seems there's no good way to do deep-serialization of objects using `Settings`. Ugh, what a ridiculous design oversight. – BlueRaja - Danny Pflughoeft Dec 27 '16 at 21:17

Why can't I serialize an object with a struct in it?

2 Answers2