C# – An object reference is required for the non-static field, method, or property ‘System.Web.UI.Page.Server.get’

asp.netcinheritanceobjectserver.mappath

So I have two functions and I'm getting an interesting problem. Essentially I'm aiming to make my code more portable in an easily includeable cs file.

Here's said cs file:

namespace basicFunctions {
public partial class phpPort : System.Web.UI.Page {
    public static string includer(string filename) {
        string path = Server.MapPath("./" + filename);
        string content = System.IO.File.ReadAllText(path);
        return content;
    }
    public void returnError() {
        Response.Write("<h2>An error has occurred!</h2>");
        Response.Write("<p>You have followed an incorrect link. Please double check and try again.</p>");
        Response.Write(includer("footer.html"));
        Response.End();
    }
}
}

Here is the page that is referencing it:

<% @Page Language="C#" Debug="true" Inherits="basicFunctions.phpPort" CodeFile="basicfunctions.cs" %>
<% @Import Namespace="System.Web.Configuration" %>

<script language="C#" runat="server">
void Page_Load(object sender,EventArgs e) {
    Response.Write(includer("header.html"));
    //irrelevant code
    if ('stuff happens') {
        returnError();
    }
    Response.Write(includer("footer.html"));
}
</script>

The error I'm getting is the one listed above, namely:

Compiler Error Message: CS0120: An object reference is required for the non-static field, method, or property 'System.Web.UI.Page.Server.get'

On the following line:

Line 5: string path = Server.MapPath("./" + filename);

Best Answer

Server is only available to instances of System.Web.UI.Page-implementations (as it's an instance property).

You have 2 options:

Convert the method from static to instance
Use following code:

(overhead of creating a System.Web.UI.HtmlControls.HtmlGenericControl)

public static string FooMethod(string path)
{
    var htmlGenericControl = new System.Web.UI.HtmlControls.HtmlGenericControl();
    var mappedPath = htmlGenericControl.MapPath(path);
    return mappedPath;
}

or (not tested):

public static string FooMethod(string path)
{
    var mappedPath = HostingEnvironment.MapPath(path);
    return mappedPath;
}

or (not that good option, as it somehow fakes to be static but rather is static for webcontext-calls only):

public static string FooMethod(string path)
{
    var mappedPath = HttpContext.Current.Server.MapPath(path);
    return mappedPath;
}

Related Solutions

C# – the difference between a field and a property

Properties expose fields. Fields should (almost always) be kept private to a class and accessed via get and set properties. Properties provide a level of abstraction allowing you to change the fields while not affecting the external way they are accessed by the things that use your class.

public class MyClass
{
    // this is a field.  It is private to your class and stores the actual data.
    private string _myField;

    // this is a property. When accessed it uses the underlying field,
    // but only exposes the contract, which will not be affected by the underlying field
    public string MyProperty
    {
        get
        {
            return _myField;
        }
        set
        {
            _myField = value;
        }
    }

    // This is an AutoProperty (C# 3.0 and higher) - which is a shorthand syntax
    // used to generate a private field for you
    public int AnotherProperty { get; set; } 
}

@Kent points out that Properties are not required to encapsulate fields, they could do a calculation on other fields, or serve other purposes.

@GSS points out that you can also do other logic, such as validation, when a property is accessed, another useful feature.

C# – CS0120: An object reference is required for the nonstatic field, method, or property ‘foo’

It looks like you are calling a non static member (a property or method, specifically setTextboxText) from a static method (specifically SumData). You will need to either:

Make the called member static also:

static void setTextboxText(int result)
{
    // Write static logic for setTextboxText.  
    // This may require a static singleton instance of Form1.
}

Create an instance of Form1 within the calling method:

private static void SumData(object state)
{
    int result = 0;
    //int[] icount = (int[])state;
    int icount = (int)state;

    for (int i = icount; i > 0; i--)
    {
        result += i;
        System.Threading.Thread.Sleep(1000);
    }
    Form1 frm1 = new Form1();
    frm1.setTextboxText(result);
}

Passing in an instance of Form1 would be an option also.

Make the calling method a non-static instance method (of Form1):

private void SumData(object state)
{
    int result = 0;
    //int[] icount = (int[])state;
    int icount = (int)state;

    for (int i = icount; i > 0; i--)
    {
        result += i;
        System.Threading.Thread.Sleep(1000);
    }
    setTextboxText(result);
}

More info about this error can be found on MSDN.

Best Answer

Related Solutions

C# – the difference between a field and a property

C# – CS0120: An object reference is required for the nonstatic field, method, or property ‘foo’

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