C# question...

Matt_Hirst

Matt_Hirst

Matt_Hirst

Associate
Joined
27 Jan 2005
Posts
1,397
Location
S. Yorks
Am trying to learn c# and am struggling!

What I have is a form with a datagrid on it, I have gone down the route of creating the datagrid dynamicly and all works fine. I am now looking to spilit the code away from the form into seperate classes and now I have done this I receive the error "Object reference not set to an instance of an object."

I have split everything out to its barest, the code was copied off MSDN.
Form1.cs
Code: 
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 dynamicDataGridControls
{
    public partial class Form1 : System.Windows.Forms.Form
    {
        public Class1 cls1 = new Class1();

        public Form1()
        {
            InitializeComponent();
        }

        private void SetupLayout()
        {
            this.Size = new Size(600, 500);
        }

        private void button3_Click(object sender, EventArgs e)
        {
            SetupLayout();
            cls1.SetupDataGridView();
            cls1.PopulateDataGridView();

        }

    }
}

Class1.cs
Code: 
            using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Windows.Forms;

namespace dynamicDataGridControls
{
    public class Class1
    {
        public Form frm1;
        public DataGridView dGridView = new DataGridView();

        public void PopulateDataGridView()
        {

            string[] row0 = { };//{ "11/22/1968", "29", "Revolution 9", "Beatles", "The Beatles [White Album]" };
            string[] row1 = { };//{ "1960", "6", "Fools Rush In", "Frank Sinatra", "Nice 'N' Easy" };
            string[] row2 = { };//{ "11/11/1971", "1", "One of These Days", "Pink Floyd", "Meddle" };
            string[] row3 = { };//{ "1988", "7", "Where Is My Mind?", "Pixies", "Surfer Rosa" };
            string[] row4 = { };//{ "5/1981", "9", "Can't Find My Mind", "Cramps", "Psychedelic Jungle" };
            string[] row5 = { };//{ "6/10/2003", "13", "Scatterbrain. (As Dead As Leaves.)", "Radiohead", "Hail to the Thief" };
            string[] row6 = { };//{ "6/30/1992", "3", "Dress", "P J Harvey", "Dry" };

        }
        
        public void SetupDataGridView()
        {
            frm1.Controls.Add(dGridView);

            dGridView.ColumnCount = 5;

            dGridView.ColumnHeadersDefaultCellStyle.BackColor = Color.Navy;
            dGridView.ColumnHeadersDefaultCellStyle.ForeColor = Color.White;
            dGridView.ColumnHeadersDefaultCellStyle.Font = new Font(dGridView.Font, FontStyle.Bold);

            dGridView.Name = "dDataGridView";
            dGridView.Location = new Point(8, 100);
            dGridView.Size = new Size(500, 250);
            dGridView.AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCellsExceptHeaders;
            dGridView.ColumnHeadersBorderStyle = DataGridViewHeaderBorderStyle.Single;
            dGridView.CellBorderStyle = DataGridViewCellBorderStyle.Single;
            dGridView.GridColor = Color.Black;
            dGridView.RowHeadersVisible = false;

            dGridView.Columns[0].Name = "Release Date";
            dGridView.Columns[1].Name = "Track";
            dGridView.Columns[2].Name = "Title";
            dGridView.Columns[3].Name = "Artist";
            dGridView.Columns[4].Name = "Album";
            dGridView.Columns[4].DefaultCellStyle.Font = new Font(dGridView.DefaultCellStyle.Font, FontStyle.Italic);

            dGridView.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
            dGridView.MultiSelect = false;
        }

    }
}

Like I say am totally nw to this so any help would be appreciated.

Mat
 
Last edited:
Hi,

The error is on frm1.Controls.Add(dGridView);

Sorry I am at the stage of ripping code out in frustration so have re editted the original post.

Matt
 
You need to assign frm1 to something before you can add controls to it. Change button3_Click() to this:

Code: 
        private void button3_Click(object sender, EventArgs e)
        {
            SetupLayout();
            cls1.frm1 = this;
            cls1.SetupDataGridView();
            cls1.PopulateDataGridView();

        }
 
Thanks for that, C# is so hard work esp. when trying to learn it!

Have now moved the following to the class and it fails once more with:

Error 1 'dynamicDataGridControls.Class1' does not contain a definition for 'Size' and no extension method 'Size' accepting a first argument of type 'dynamicDataGridControls.Class1' could be found (are you missing a using directive or an assembly reference?) C:\Carriage Coster\VS New\dynamicdatagrid\dynamicDataGridControls\dynamicDataGridControls\Class1.cs 62 18 dynamicDataGridControls


Any pointers for this?

Mat
 
Just a quick note about the design.
Personally, I'd have your Class1 create a DataGridView object and then return a reference to this.
Then in the Form you can have something like
Code: 
DataGridView grid = cls1.CreateDataGridView();
Controls.Add(grid);

Class1 then doesn't need to know anything about the Form and just deals with the DataGridView stuff and could potentially be reused in other scenarios.

I realise you're probably quite new to this and it may seem like a minor point, but if you learn about proper class design, it will save you lots of pain in the future so I would urge you to take it into account.
 
So I would have :

Code: 
 DataGridView grid = clsForm.CreateDataGridView();
 Controls.Add(grid);

in the actual form and then the following in the class?

Code: 
 public void CreateDataGridView()
        {
            DataGridView dGridView = new DataGridView();
            dGridView.ColumnHeadersDefaultCellStyle.BackColor = Color.Navy;
            dGridView.ColumnHeadersDefaultCellStyle.ForeColor = Color.White;
            dGridView.Name = "dDataGridView";
            dGridView.Location = new Point(130, 370);
            dGridView.Size = new Size(405, 150);
            dGridView.ColumnHeadersBorderStyle = DataGridViewHeaderBorderStyle.Single;
            dGridView.CellBorderStyle = DataGridViewCellBorderStyle.Single;
            dGridView.RowHeadersVisible = false;
            dGridView.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
            dGridView.MultiSelect = false;
        }

regards,

Matt
 
The return type of that method is void, which means it doesn't return anything.
You'd need to change the return type to be DataGridView and then return your created object to the calling method. Something like this

Code: 
 public DataGridView CreateDataGridView()
        {
            DataGridView dGridView = new DataGridView();
            dGridView.ColumnHeadersDefaultCellStyle.BackColor = Color.Navy;
            dGridView.ColumnHeadersDefaultCellStyle.ForeColor = Color.White;
            dGridView.Name = "dDataGridView";
            dGridView.Location = new Point(130, 370);
            dGridView.Size = new Size(405, 150);
            dGridView.ColumnHeadersBorderStyle = DataGridViewHeaderBorderStyle.Single;
            dGridView.CellBorderStyle = DataGridViewCellBorderStyle.Single;
            dGridView.RowHeadersVisible = false;
            dGridView.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
            dGridView.MultiSelect = false;

            return dGridView;
        }
 
Ok, think I am getting somewhere, have transfered a lot of my code out to logical classes but I have now an error on this line:

Code: 
                    txt.Leave += new EventHandler(txt_Exit);


Error is:
Error 1 The name 'txt_Exit' does not exist in the current context C:\Carriage Coster\VS New\CarriageCosts\CarriageCosts\clsForm.cs 101 51 CarriageCosts

I dynamicly create txtboxes and then add an eventhandler for these text boxes, the event handler is on one of the forms. So how do I do this?

Matt
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom