Access class fields from partial class

Question

I'm currently in a scenario in which I have to make use of partial classes. In this partial class I have a few methods that need to address fields in the other class.

for example

Edit: I'm sorry: the first class is already declared partial!

public partial class myClass
{        
    private string _myString;

    public string myString
    {
        get { return _myString; }
        set { _myString = value; }
    }
}

and

public partial class myClass
{
    public void doSomething()
    {
        myString = "newString";
    }
}

The compiler says myString doesn't exist in the partial class!

How can I overcome this problem?

Sven · Answer 1 · 2018-03-14T16:04:41.400

42

A common problem is having the partial classes in different namespaces. Namespaces are part of the Class name, namespace1.myClass and namespace.a.myClass are handled as two completely seperate classes.

According to MSDN, each part of a partial class should:

have the partial modifier
have the same class name
be in the same namespace
be in the same assembly or DLL
have the same visibility (like public, private, etc)

edited Mar 14 '18 at 16:04

answered Nov 09 '10 at 11:18

Sven

2,839
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I would like to add that if one partial implements an interface, the other partials should include the same declaration. The actual interface methods only need to be implemented in one of the files, but the partial class declarations need to match. – SixOThree Apr 08 '22 at 15:46

score 15 · Accepted Answer · edited Jun 09 '21 at 14:09

There are a few things you need to fix with the code you posted:

When using partial classes in C# all parts of the class must be declared as partial classes

You have:

 public class myClass {}
 public partial class myClass {}

Which needs to become:

public partial class myClass {}
public partial class myClass {}

Secondly, you're trying to set:

myString="newString";

but myString is a public property without a setter.

So either you add a setter when declaring myString:

public string myString
{
    get{ return _myString; }
    set { _myString = value; }
}

or just use:

_myString="newString";

in your second partial class file.

score 1 · Answer 3 · answered Nov 09 '10 at 11:18

1

When I put your code into Visual Studio I got a different error:

myString = "newString";
Error   Property or indexer 'ConsoleApplication1.Program.myClass.myString' cannot be assigned to -- it is read only

If I change it to this, it works fine:

_myString = "newString";

Edit:

You don't need to mark a class as partial in both palaces, this compiles fine:

    public class myClass
    {

        private string _myString;

        public string myString
        {
            get { return _myString; }
        }
    }


    public partial class myClass
    {

        public void doSomething()
        {
            _myString = "newString";
        }

    }

answered Nov 09 '10 at 11:18

Pondidum

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While it might compile fine, in the documentation it says its required. Its probably a good idea to do it anyway to be consistent, and future proof. – Khalos Nov 09 '10 at 11:25
I just followed what the forms designer does...naughty winForms designer! – Pondidum Nov 09 '10 at 11:28
I had the same problem until I noticed that my method was static. Duh! – Howard Rubin Jul 14 '15 at 21:43

score 1 · Answer 4 · answered Nov 09 '10 at 11:18

Assuming that both declaration refer to the same namespace, your first declaration does not contain the partial keyword:

Using the partial keyword indicates that other parts of the class, struct, or interface can be defined within the namespace. All the parts must use the partial keyword. All of the parts must be available at compile time to form the final type. All the parts must have the same accessibility, such as public, private, and so on.public, private, and so on.

http://msdn.microsoft.com/en-en/library/wa80x488(v=VS.80).aspx

score 0 · Answer 5 · answered Nov 09 '10 at 11:16

0

You simply have to mark the class as partial in both places, not just one of them.

answered Nov 09 '10 at 11:16

Øyvind Bråthen

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Access class fields from partial class

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