An exception thrown that I can't figure out how to fix

Darrall

This is from a tutorial from Home & Learn: http://www.homeandlearn.co.uk/csharp/csharp_s13p3.html[^] The problem I am having is with an uninitialized variable but I can't figure out how to do it:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Multiple_Forms
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
Form2 secondForm = new Form2();
public static TextBox tb = new TextBox();

    private void btnFormTwo\_Click(object sender, EventArgs e)
    {
        secondForm.ShowDialog();
    }

    private void Form1\_Load(object sender, EventArgs e)
    {
        
        tb = txtChangeCase;
    }
}

}

The problem is with the last line. I can see why...just can't figure out what to do to fix it. Anyone know the answer?

Lost User

Why is tb static? What is txtChangeCase? And what is the exception? (I can only think of 1 case where a direct assignment to a field (not through an indexer or anything like that) could throw an exception: when there is an implicit cast that throws an exception (which is rare))

Darrall

This is a multi form Windows Application and apparently that code is to allow interaction between Form1 and Form2. If you'd like you can look at the whole lesson at the following site: http://www.homeandlearn.co.uk/csharp/csharp_s13p3.html[^]

Lost User

That tutorial fails on so many levels that I would advice against ever even thinking about it, but I'd like someone else's opinion about that too I mean come on: - a static textbox as a way to communicate between forms (please no.) - creating a new textbox and then almost immediately afterward throwing it away without ever having used it (why?) - writing ==true (seriously, wtf, you might as well write if((x == true) == true && x != false) just to be very sure that x is indeed true) - referring to a computer program as "programme". huh? shows lack of knowledge of the jargon IMO, and I already got the impression that the writer of that tutorial is a noob (he also uses CreateGraphics inside the Paint event later on)

Dan Mos

that is not a tuturial. It's a what to avoid tutorial. linkig two forms by static fields => really bad any many other stuff. Don't use that site unless you want to become a rumorous c# developer.

Luc Pattyn

I hadn't seen that site before, judging from that one page it isn't worth a penny, it being inaccurate and confusing. Buy and study a book, you may learn all you need and more in less than a week. This[^] explains my view on books. Trying to learn from a free site only gives you what you paid for, i.e. nothing much. :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.
[The QA section does it automatically now, I hope we soon get it on regular forums as well]

Luc Pattyn

harold aptroot wrote:

he also uses CreateGraphics inside the Paint event

he is to be shot on sight! :eek:

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.
[The QA section does it automatically now, I hope we soon get it on regular forums as well]

DaveyM69

Ditto the comments from the others. Probably the most correct way to acheive the result that the tutorial was aiming for would be to: 1. Create a Case enum. 2. Have a private field of type Case in the dialog form that is set according to the radio buttons and expose this field in a public read only property. 3. Check the DialogResult of the dialog form in the main form, if OK then read the property before disposing of the form. 4. Use the Case obtained from the property in a switch block and change the TextBox's Text property accordingly. What is it you were wanting to learn from that tutorial - changing the case of a string, using a dialog to get a user selection that may be returned to the instanciating form, or general inter-object communication?

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Why are you using VB6? Do you hate yourself? (Christian Graus)

AspDotNetDev

Luc Pattyn wrote:

Trying to learn from a free site only gives you what you paid for, i.e. nothing much.

I don't know, I can think of at least one site that is free and is a pretty good learning resource. It may not compare to a book, but it is a little more than "nothing much". :rolleyes:

[Forum Guidelines]

Luc Pattyn

that must be an exceptional site then. :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.
[The QA section does it automatically now, I hope we soon get it on regular forums as well]

Darrall

Thanks Dave. Basically the idea was to introduce using multiforms with the second form used to perform the changes on the first form. As you have all pointed out I am obviously using a poor source of information.

DaveyM69

I'll knock you up a simple demo this weekend and post back here if that would be helpful. Colin Mackay has an article here[^] about passing data between forms. It's .NET 1.1 IIRC but the principles are still valid :thumbsup: In this situation, you only need the simpler Parent to Child relationship as that method can be used for both writing to and reading from properties. The Child to Parent is only needed when the Child needs to inform the parent when something has changed.

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Darrall

Thanks Dave...I'd appreciate that. You are the first one that has given me any kind of answer. I know the tutorial I am using is crappy but I'd still like to solve this particular problem. Thanks again. Darrall

DaveyM69

OK, this does the same as the tutorial but it does it correctly. I have included an example of both Parent to Child (Parent reads a property in the child) and Child to Parent (Parent listens for event that the Child raises). For a beginners tutorial to events, have a look at my Events Made Simple article[^]. Anyway, here's the code - any questions, just ask! I've included all the control creation and initialization so you can copy and paste and it should work without having to add any controls in the designer.

// Case.cs
public enum Case
{
None,
Upper,
Lower,
Proper
}

// FormChild.cs
using System;
using System.Drawing;
using System.Windows.Forms;

public partial class FormChild : Form
{
#region Events

public event EventHandler SelectedCaseChanged;

#endregion

#region Fields

private Case selectedCase;

/\* Would normally be in the Designer.cs file \*/
private RadioButton radioUpper;
private RadioButton radioLower;
private RadioButton radioProper;
private Button buttonOK;
private Button buttonCancel;

#endregion

#region Constructors

public FormChild()
{
    InitializeComponent();
    CustomInitialize();

    selectedCase = Case.None;
    radioUpper.Tag = Case.Upper;
    radioLower.Tag = Case.Lower;
    radioProper.Tag = Case.Proper;
}

#endregion

#region Properties

/\* Public read only public property \*/
public Case SelectedCase
{
    get { return selectedCase; }
    private set
    {
        if (selectedCase != value)
        {
            selectedCase = value;
            OnSelectedCaseChanged(EventArgs.Empty);
        }
    }
}

#endregion

#region Methods

private void RadioButton\_CheckedChanged(object sender, EventArgs e)
{
    RadioButton selectedRadio = sender as RadioButton;
    if (sender != null)
        SelectedCase = (Case)selectedRadio.Tag;
}

protected virtual void OnSelectedCaseChanged(EventArgs e)
{
    EventHandler eh = SelectedCaseChanged;
    if (eh != null)
        eh(this, e);
}

/\* Creates all controls and sets properties
 \* Would normally be in the Deisgner.cs file \*/

Darrall

Thank you so much for your time and effort. I have spent all day at this and finally got it to work but yours looks much tidier. I will try it out tomorrow and let you know. Thanks again. Darrall

DaveyM69

No problem :-D In addition to my article I previously linked to, I have posted a Tip/Trick here[^] which is a little more concise and should help in understanding the basics of raising/handling events.

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Darrall

Thanks again :) With all your help I should come out on top...maybe