Method Not Recognized

Question

This code I am working on is not working properly. It displays this error when hello() is invoked:

nameThisString "does not exist in the current context"

I have the overall code structure (it's simplified greatly to get to the point). What is wrong with my code?

using System.Windows.Controls;

namespace Application3
{
    public partial class MainView : UserControl
    {
        public SecondClass secondClass;
        public MainView()
        {
            InitializeComponent();
            hello();    
        }

        private void hello()
        {
            secondClass.nameThisString("hello");
        }        
    }

    public class SecondClass
    {
        public void nameThisString(string what)
        {
            what = "me";
        }    
    }    
}

Maybe you simplified too much? ([ideone](http://ideone.com/yCCnuv)) — Uwe Keim, Jan 06 '16 at 14:31
The code you've provided doesn't display the problem you've claimed. Please produce a [mcve]. — Jon Skeet, Jan 06 '16 at 14:32
I'm with @UweKeim. Does this simplified version actually still reproduce your problem? I don't see anything wrong with it. — DrewJordan, Jan 06 '16 at 14:32
The only thing this code will produce is a `NullReferenceException` - you've never instantiated `SecondClass`. — Jamiec, Jan 06 '16 at 14:33
You declare secondClass, but you never instantiate it. Maybe if you did 'public SecondClass secondClass = new SecondClass()' — Taegost, Jan 06 '16 at 14:33
Sorry it's giving me the error "Additional information: Object reference not set to an instance of an object." — Sean, Jan 06 '16 at 14:35
Sorry I am new, but doesn't "public SecondClass secondClass;" create an instance? — Sean, Jan 06 '16 at 14:35
Well that's a completely different error! It's an exception rather than the compile-time error you talked about before. — Jon Skeet, Jan 06 '16 at 14:35
And no, it doesn't. It declares a field, which has a default value of `null`. — Jon Skeet, Jan 06 '16 at 14:35
@Sean Nope, declaring the variable doesn't create an instance of that class. — ChrisF, Jan 06 '16 at 14:36
I was getting both errors. The first was before I compiled and the next was while it was trying to compile. @ChrisF, how are declaring and creating an instance different? Thank you for the clarification. — Sean, Jan 06 '16 at 14:39

score 4 · Answer 1 · answered Jan 06 '16 at 14:36

4

Per your posted code, there is only one way you can get the said error; if you have called your method like below instead of secondClass.nameThisString("hello");

    private void hello()
    {
        nameThisString("hello");
    }

Per your comment you are getting a NullRef exception cause you have just defined the variable but haven't created an instance for it. change your code to be like

    public SecondClass secondClass;
    public MainView()
    {
        InitializeComponent();
        secondClass = new SecondClass(); // create an instance
        hello();    
    }

answered Jan 06 '16 at 14:36

Rahul

76,197
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Thanks! What is the difference between defining a variable and creating an instance? IE why would you just define it and not create it? – Sean Jan 06 '16 at 14:46
if you say `int a` you are just defining or declaring a int variable but creating a instance is nothing but when you assign a value for it and say `a = 100`. though INT is value type ... for a reference type like class `SecondClass secondClass` you have just declared the variable and it's null right now (or) doesn't point to any object in heap and so you will have to create a instance by using the `new` operator. Consider learning about OOP more first. – Rahul Jan 06 '16 at 14:49
Thank you for the explanation. – Sean Jan 06 '16 at 14:51
@Rahul `int` is perhaps the worst example you could have given - `int a` *does* give it a value (`0`) due to its type. Classes behave differently. – Jamiec Jan 06 '16 at 14:58
@Jamiec, that's kind a for simplicity. – Rahul Jan 06 '16 at 15:03

Maxim Fleitling · Answer 2 · 2016-01-06T14:34:03.337

3

You have to create an instance of the SecondClass in the constructor of the MainView class first.

edited Jan 06 '16 at 14:34

answered Jan 06 '16 at 14:33

Maxim Fleitling

542
4
14

In your constructor - `secondClass = new SecondClass()` – Alex Jan 06 '16 at 14:33
5

This wouldn't cause the error mentioned - would be a null ref ... – PaulB Jan 06 '16 at 14:34
@PaulB which is actually the problem (as revealed in the comments) – ChrisF Jan 06 '16 at 14:36
True - though I commented before that was revealed ... :) – PaulB Jan 06 '16 at 14:37

score 0 · Answer 3 · answered Jan 06 '16 at 14:36

0

You forgot to instantiate the class; use like this:

 public SecondClass secondClass;
 public MainView()
  {
    InitializeComponent();
    SecondClass = new SecondClass();
    hello();
  }

Or simply:

public SecondClass secondClass=new SecondClass();

answered Jan 06 '16 at 14:36

sujith karivelil

28,671
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Method Not Recognized

3 Answers3