object reference not set to an instance of an object

[Latheesan]

Hello, Im trying to workout how to dynamically add tab pages with RichTextBox inside them. So far: 1. I have a form with a input field to enter how many tab pages to create 2. A button that calls the method to create tab page when clicked 3. a tabcontrol with no pages on it Here is a demo - http://img525.imageshack.us/img525/4519/untitledxv6.jpg[^] This is the code i have on form1.cs static int maxTabs = 20; TabPage[] tabPages = new TabPage[maxTabs]; SyntaxHighlightingTextBox[] shtb; private void AddTab(int tabNumber) { for (int i = 0; i < tabNumber; i++) { // Create a new tab tabPages[tabNumber] = new TabPage(); tabPages[tabNumber].Location = new System.Drawing.Point(4, 22); tabPages[tabNumber].Name = "tabPage" + tabNumber.ToString(); tabPages[tabNumber].Padding = new System.Windows.Forms.Padding(3); tabPages[tabNumber].Size = new System.Drawing.Size(403, 386); tabPages[tabNumber].TabIndex = tabNumber; tabPages[tabNumber].Text = "tabPage " + tabNumber.ToString(); tabPages[tabNumber].UseVisualStyleBackColor = true; // Create a new RichTextBox inside the tab shtb[tabNumber] = new SyntaxHighlightingTextBox(); shtb[tabNumber].Name = "shtb" + tabNumber.ToString(); shtb[tabNumber].Location = new Point(0, 0); shtb[tabNumber].Dock = DockStyle.Fill; // Add Tab and RichTextBox Control tabPages[tabNumber].Controls.Add(shtb[tabNumber]); tabControl.Controls.Add(tabPages[tabNumber]); // Reset of tabControl tabPages[tabNumber].SuspendLayout(); tabPages[tabNumber].ResumeLayout(false); int counter = tabControl.Controls.Count; tabControl.SelectedIndex = counter - 1; this.Text = "TabText1 - " + tabPages[tabNumber].Text; } } private void AddButton_Click(object sender, EventArgs e) { try { AddTab(int.Parse(tabNumberTextBox.Text)); } catch (Exception ex)

[PIEBALDconsult]

I suspect this: SyntaxHighlightingTextBox[] shtb; it's not initialized. I also wonder why you have arrays of TabPages and SyntaxHighlightingTextBoxes.

[Latheesan]

If its not getting initialized, should i move the code inside: public Form1() { InitializeComponent(); } I have an array of tabpages and shtbs because, i want to be able to many many instances of tabs with richtextboxes inside them, dynamically on demand.

[Latheesan]

I tried entering 0 into the input box and try to add a tab, this time no exception error, but instead, nothing happens. Where im i going wrong? Why wont this work?

[Latheesan]

Okay, i made a silly mistake in the for loop, but here's the fixed version of the for loop code: for (int i = 0; i < tabNumber; i++) { // Create a new tab tabPages[i] = new TabPage(); tabPages[i].Location = new System.Drawing.Point(4, 22); tabPages[i].Name = "tabPage" + i.ToString(); tabPages[i].Padding = new System.Windows.Forms.Padding(3); tabPages[i].Size = new System.Drawing.Size(403, 386); tabPages[i].TabIndex = i; tabPages[i].Text = "tabPage " + i.ToString(); tabPages[i].UseVisualStyleBackColor = true; // Create a new RichTextBox inside the tab shtb[i] = new SyntaxHighlightingTextBox(); shtb[i].Name = "shtb" + i.ToString(); shtb[i].Location = new Point(0, 0); shtb[i].Dock = DockStyle.Fill; // Add Tab and RichTextBox Control tabPages[i].Controls.Add(shtb[i]); tabControl.Controls.Add(tabPages[i]); // Reset of tabControl tabPages[i].SuspendLayout(); tabPages[i].ResumeLayout(false); int counter = tabControl.Controls.Count; tabControl.SelectedIndex = counter - 1; this.Text = "TabText1 - " + tabPages[i].Text; } This compiles correctly, yet, when i run it, i get the exception error again...

[PIEBALDconsult]

Note the difference between these two statements: TabPage[] tabPages **= new TabPage[maxTabs];** SyntaxHighlightingTextBox[] shtb;

[PIEBALDconsult]

Latheesan wrote:

I have an array of tabpages and shtbs because, i want to be able to many many instances of tabs with richtextboxes inside them, dynamically on demand.

You don't need arrays for that, the TabControl and TabPage have Collections for them.

[Latheesan]

Oh? i didnt know that, Is there any example on how to use this? I haven't seen any good tutorials on tab pages anywhere yet. I did do a bit research tho.

[Latheesan]

I saw the difference in the code, however, when i changed the code like this (before when i was doing some trial and error): TabPage[] tabPages = new TabPage[maxTabs]; SyntaxHighlightingTextBox[] shtb = new SyntaxHighlightingTextBox(); I started to get this error message: Cannot implicitly convert type 'SynHighLib.SyntaxHighlightingTextBox' to 'SynHighLib.SyntaxHighlightingTextBox[]'

[PIEBALDconsult]

As you should, try SyntaxHighlightingTextBox[] shtb = new SyntaxHighlightingTextBox**[somevalue]**;

[Latheesan]

OMG... that worked O_O; Thank you very much :)

[PIEBALDconsult]

Here's my version: (I used a RichTextBox because I don't know what that other thing is.)

    private void AddTabs ( int tabNumber )
    {
        System.Windows.Forms.TabPage tabPage = null ;
        System.Windows.Forms.RichTextBox shtb;

        tabControl.SuspendLayout() ;
        
        tabControl.Controls.Clear() ;
        
        for (int i = 0; i < tabNumber; i++)
        {
            // Create a new tab
            tabPage = new System.Windows.Forms.TabPage();
            tabPage.Location = new System.Drawing.Point(4, 22);
            tabPage.Name = "tabPage" + i.ToString();
            tabPage.Padding = new System.Windows.Forms.Padding(3);
            tabPage.Size = new System.Drawing.Size(403, 386);
            tabPage.TabIndex = i;
            tabPage.Text = "tabPage " + i.ToString();
            tabPage.UseVisualStyleBackColor = true;

            // Create a new RichTextBox inside the tab
            shtb = new System.Windows.Forms.RichTextBox();
            shtb.Name = "shtb" + i.ToString();
            shtb.Location = new System.Drawing.Point(0, 0);
            shtb.Dock = System.Windows.Forms.DockStyle.Fill;

            // Add Tab and RichTextBox Control
            tabPage.Controls.Add(shtb);
            tabControl.Controls.Add(tabPage);

            // Reset of tabControl
            tabPage.SuspendLayout();
            tabPage.ResumeLayout(false);
        }

        this.Text = "TabText1 - " + tabPage.Text;
        
        tabControl.SelectedIndex = tabControl.Controls.Count - 1;
        
        tabControl.ResumeLayout() ;
    }

[PIEBALDconsult]

Of course it does. Now donate a pint of blood to the Red Cross.

[Christian Graus]

I recommend if you're coding blind and trying things to see if they work, you buy a C# book and work through it.

Christian Graus - Microsoft MVP - C++ Metal Musings - Rex and my new metal blog "I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )