It means that either:
1) A class needs to be instantiated with "new", but was not done so.
or
2) A class has been instantiated BUT you assigned Nothing (VB) or null
(C#) to it,
and then you attempted to use the methods from it.
Kindly look at the code again.
Cheers!
Benj
On May 28, 5:04 pm, sahm <sahm...@gmail.com> wrote:
> Hi every one
>
> Good Day
>
> I still get this error
> /////////////////////////////////////
> Object reference not set to an instance of an object
> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> Best
>
> Salim
>
> On May 18, 4:28 am, CallMeLaNN <nalz...@gmail.com> wrote:
>
> > I thought you want to use MDI for login form.
>
> > If so, you need to add log.MdiParent = this; here:
>
> > Login log = new Login();
> > log.MdiParent = this;
> > log.Show();
>
> > Note: to make your login visible, place the checkUser(); not in
> > "public Main()" constructor but in Main_Load().
>
> > The "Object reference not set to an instance of an object" is because
> > of your
> > ParentForm or this.MdiParent is null at here:
>
> > Main ParentForm = (Main)this.MdiParent;
>
> > and sure will throw the error when you use it:
> > ParentForm.menuStrip1.Enabled = false;
>
> > On May 17, 2:10 pm, sahm <sahm...@gmail.com> wrote:
>
> > > Hi every One
>
> > > Good Day
>
> > > I'm still having problem with this
> > > I write the code like this
>
> > > ////////////////////////////////////
> > > Login log = new Login(this);
> > > log.ShowDialog();
> > > \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> > > this error is showing
> > > ///////////////////////////////////////
> > > Error 1 'Archive_System.Login' does not contain a constructor that
> > > takes '1' arguments E:\Projects\C#\Archive System\Archive System
> > > \MainForm.cs 68 25 Archive System
>
> > > \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> > > and if I writ is like this
> > > //////////////////////////////
> > > Login log = new Login();
> > > log.ShowDialog(this);
> > > \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> > > Run time error is showing after I Enter the user name and the password
> > > ///////////////////////////////////
> > > Object reference not set to an instance of an object
> > > \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> > > and this is my code
>
> > > MainForm
> > > /////////////////////////////////////
> > > 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;
> > > using System.Management;
>
> > > namespace Archive_System
> > > {
> > > public partial class Main : Form
> > > {
> > > public Main()
> > > {
> > > try
> > > {
> > > InitializeComponent();
> > > this.WindowState = FormWindowState.Maximized;
> > > this.FormBorderStyle = FormBorderStyle.FixedSingle;
> > > this.Closing += new CancelEventHandler(Form_Closing);
>
> > > this.menuStrip1.Enabled = false;
> > > //this.Enabled = false;
> > > checkUser();
> > > }
> > > catch (Exception exp)
> > > {
> > > string ms = exp.Message;
> > > MessageBox.Show(this, ms, "System Error",
> > > MessageBoxButtons.OK, MessageBoxIcon.Error);
>
> > > }
> > > }
>
> > > System.Data.SqlClient.SqlConnection con;
>
> > > private void userToolStripMenuItem_Click(object sender,
> > > EventArgs e)
> > > {
> > > try
> > > {
> > > createUser cu = new createUser();
> > > cu.MdiParent = this;
> > > cu.Show();
>
> > > }
> > > catch (Exception exp)
> > > {
> > > string ms = exp.Message;
> > > MessageBox.Show(this, ms, "System Error",
> > > MessageBoxButtons.OK, MessageBoxIcon.Error);
> > > }
> > > }
>
> > > private void aboutToolStripMenuItem_Click(object sender,
> > > EventArgs e)
> > > {
> > > About ab = new About();
> > > ab.MdiParent = this;
> > > ab.Show();
> > > }
> > > /*public void setPreviousForm(frmMain mainFrm)
> > > {
> > > prevForm = mainForm;
> > > }*/
> > > public void checkUser()
> > > {
> > > Login log = new Login();
> > > //log.setPreviousForm(this);
> > > log.ShowDialog(this);
>
> > > }
>
> > > private void Main_Load(object sender, EventArgs e)
> > > {
> > > con = new System.Data.SqlClient.SqlConnection();
> > > con.ConnectionString = "Data Source=mr-x\
> > > \SQLExpress2008;Initial Catalog=archive;Integrated Security=True";
> > > con.Open();
>
> > > }
>
> > > public void Form_Closing(object sender, CancelEventArgs cArgs)
> > > {
> > > con.Close();
>
> > > }
>
> > > private void menuStrip1_ItemClicked(object sender,
> > > ToolStripItemClickedEventArgs e)
> > > {
>
> > > }
>
> > > }}
>
> > > \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> > > Login
> > > /////////////////////////////////////
> > > 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 Archive_System
> > > {
> > > public partial class Login : Form
> > > {
> > > public Login()
> > > {
> > > InitializeComponent();
> > > }
> > > //private static new MainForm ParentForm = null;
>
> > > /*public Login(MainForm APrent):this()
> > > {
> > > Main ParentForm =(Main) this.MdiParent;
> > > }*/
>
> > > private void OKbutton_Click(object sender, EventArgs e)
> > > {
> > > string un = userNametextBox.Text;
> > > string ps = PasswardMaskedTextBox.Text;
>
> > > if (un == "sahm" || ps == "java")
> > > {
> > > MessageBox.Show(this, "Login Work", "",
> > > MessageBoxButtons.OK, MessageBoxIcon.Information);
> > > //ParentForm.menuStrip1.Enabled = !
> > > ParentForm.menuStrip1.Enabled;
> > > Main ParentForm = (Main)this.MdiParent;
> > > ParentForm.menuStrip1.Enabled = false;
>
> > > }
> > > else
> > > {
> > > MessageBox.Show(this, "Login not work", "",
> > > MessageBoxButtons.OK, MessageBoxIcon.Information);
> > > }
>
> > > }
>
> > > private void CancelButton_Click(object sender, EventArgs e)
> > > {
> > > this.Close();
> > > }
>
> > > }}
>
> > > \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>
> > > Thank every one
>
> > > Best
>
> > > Salim
>
> > > On May 16, 10:45 am, sahm <sahm...@gmail.com> wrote:
>
> > > > Hi CallMeLann
>
> > > > Thank for your help I'll try this
>
> > > > Best
> > > > Salim
>
> > > > On May 15, 11:23 am, CallMeLaNN <nalz...@gmail.com> wrote:
>
> > > > > Because you use:
>
> > > > > Login log = new Login();
>
> > > > > In MainForm but you declare:
>
> > > > > public Login(MainForm APrent):this()
>
> > > > > Which LoginForm need APrent value that is MainForm.
> > > > > To solve change to this:
>
> > > > > Login log = new Login(this);
>
> > > > > But, I recommend u to use MdiParent instead.
>
> > > > > 1. Remove the "private static new MainForm ParentForm = null;" no need
> > > > > to use this.
> > > > > 2. login constructor: let it default constructor (no parameter):
> > > > > "public Login()"
> > > > > 3. To disable the menu use like this: (Im not sure your main form type
> > > > > is Main or MainForm based on your code, I assume Main)
>
> > > > > Main ParentForm = (Main) this.MdiParent
> > > > > ParentForm.menuStrip1.Enabled = False
>
> > > > > dont use ! for toggle it, it can be wrong toggle, instead, assign true
> > > > > or false if you sure.
>
> > > > > On May 14, 4:01 pm, sahm <sahm...@gmail.com> wrote:
>
> > > > > > Hi Benj Nunez
>
> > > > > > Good Day
>
> > > > > > I try to do that but some error show up
> > > > > > and this is my code
>
> > > > > > the child form
> > > > > > ////////////////////////////////////////////////////
>
> > > > > > 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 Archive_System
> > > > > > {
> > > > > > public partial class Login : Form
> > > > > > {
> > > > > > public Login()
> > > > > > {
> > > > > > InitializeComponent();
> > > > > > }
> > > > > > private static new MainForm ParentForm = null;
>
> > > > > > public Login(MainForm APrent):this()
> > > > > > {
> > > > > > ParentForm = APrent;
> > > > > > }
>
> > > > > > private void OKbutton_Click(object sender, EventArgs e)
> > > > > > {
> > > > > > string un = userNametextBox.Text;
> > > > > > string ps = PasswardMaskedTextBox.Text;
>
> > > > > > if (un == "sahm" || ps == "java")
> > > > > > {
> > > > > > MessageBox.Show(this, "Login Work", "",
> > > > > > MessageBoxButtons.OK, MessageBoxIcon.Information);
> > > > > > ParentForm.menuStrip1.Enabled = !
> > > > > > ParentForm.menuStrip1.Enabled;
>
> > > > > > }
> > > > > >
>
> ...
>
> read more »
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