在连接字符串中设置SQL Server名称不起作用

Question

I have Formselectserver where get the name of a SQL Server from a combobox. Also I have form2 where is main form.

I send combobox.selectedvalue to connection string in form2 but that does not work.

I want user select one SQL Server in network and connect to it.

Formselectserver objfrmserver = new Formselectserver();

private const string strconnection = 
    @"server='" + objfrmserver.cmbshowallsqlserver.SelectedValue + 
    "';database = anfd; Integrated Security = SSPI";

The error is:

An object reference is required for the non-static field, method, or property 'exportdatafromholoo.Form1.objfrmserver'

Answer 1

Two things are wrong:

• A const values HAS to be resolved during compile time, not during runtime. You are using a runtime value. Just remove the const .
• Your field is a private field, so it is a member of your class. Is your objfrmserver also a member of that same class? You cannot initialize fields in the same class with each other. Move your initialization to the constructor.

Try this:

public void MyMethod()
{
    Formselectserver objfrmserver = new Formselectserver();
    string strconnection = @"server='" + objfrmserver.cmbshowallsqlserver.SelectedValue + "';database = anfd; Integrated Security = SSPI";
}

Answer 2

A const is a compile-time constant, so can only involve things that are known at compile-time - basically, literals.

objfrmserver is an instance (per-object) field that is a reference to another object, at runtime. This will not work. So basically, your strconnection cannot be a const . I suspect there's also not much purpose in it being a field. But as a variable it might make sense, ie

public void Connect() {
      var strconnection = @"server='" + objfrmserver.cmbshowallsqlserver.SelectedValue + "';database = anfd; Integrated Security = SS=PI";
      var conn = new SqlConnection(strconnection);
      conn.Open();
      // etc...
}

You might also want to look at SqlConnectionStringBuilder , to avoid having to know the escaping rules associated with server-names.