How to access an object property from another class?

System.Windows.Forms.Button btnAdd = (System.Windows.Forms.Button)frmMisc.Controls["groupBox1"].Controls["buttonOAdd"];

Now it works. Thanks

Ah, the buttons are actually contained in a groupbox rather than directly on the form so they won't actually appear in the form's controls collection but they will appear in the groupbox's controls collection.

So, you need something like this:

         private void buttonUniAdd_Click(object sender, EventArgs e)
        {
            testProg.Form1 frmTest = (testProg.Form1)System.Windows.Forms.Application.OpenForms["Form1"];
            System.Windows.Forms.GroupBox gbx = (System.Windows.Forms.GroupBox)
frmtest.Controls["groupBox1"];
            System.Windows.Forms.Button thisBtn = (System.Windows.Forms.Button)sender;
            System.Windows.Forms.Button btnDel = (System.Windows.Forms.Button)gbx.Controls["buttonODelete"]; // this seems to be name rather than buttonODel
            thisBtn.Text = "&Cancel";
            btnDel.Enabled = false; 
        }

here are the full code:

testclass.cs:

using System;
using System.Collections.Generic;
using System.Text;

namespace clTestProg
{
    public class testClass
    {

        public void InitControls(System.Windows.Forms.GroupBox gbx)
        {
            System.Windows.Forms.Button buttonODelete = new System.Windows.Forms.Button();
            System.Windows.Forms.Button buttonOUpdate = new System.Windows.Forms.Button();
            System.Windows.Forms.Button buttonOAdd = new System.Windows.Forms.Button();
            //
            // buttonODelete
            //
            buttonODelete.Location = new System.Drawing.Point(251, 324);
            buttonODelete.Name = "buttonODelete";
            buttonODelete.Size = new System.Drawing.Size(75, 23);
            buttonODelete.TabIndex = 0;
            buttonODelete.Text = "&Delete";
            buttonODelete.UseVisualStyleBackColor = true;
            buttonODelete.Click += new System.EventHandler(buttonUniDel_Click);
            //
            // buttonOUpdate
            //
            buttonOUpdate.Location = new System.Drawing.Point(170, 324);
            buttonOUpdate.Name = "buttonOUpdate";
            buttonOUpdate.Size = new System.Drawing.Size(75, 23);
            buttonOUpdate.TabIndex = 0;
            buttonOUpdate.Text = "&Update";
            buttonOUpdate.UseVisualStyleBackColor = true;
            buttonOUpdate.Click += new System.EventHandler(buttonUniEdit_Click);
            //
            // buttonOAdd
            //
            buttonOAdd.Location = new System.Drawing.Point(89, 324);
            buttonOAdd.Name = "buttonOAdd";
            buttonOAdd.Size = new System.Drawing.Size(75, 23);
            buttonOAdd.TabIndex = 0;
            buttonOAdd.Text = "&Add";
            buttonOAdd.UseVisualStyleBackColor = true;
            buttonOAdd.Click += new System.EventHandler(buttonUniAdd_Click);

            gbx.Controls.Add(buttonODelete);
            gbx.Controls.Add(buttonOUpdate);
            gbx.Controls.Add(buttonOAdd);
        }

        private void buttonUniAdd_Click(object sender, EventArgs e)
        {
            testProg.Form1 frmTest = (testProg.Form1)System.Windows.Forms.Application.OpenForms["Form1"];
            System.Windows.Forms.Button thisBtn = (System.Windows.Forms.Button)sender;
            System.Windows.Forms.Button btnDel = (System.Windows.Forms.Button)frmTest.Controls["buttonODel"];
            thisBtn.Text = "&Cancel";
            btnDel.Enabled = false;

        }

Form1.cs:

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

namespace testProg
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void buttonTest_Click(object sender, EventArgs e)
        {
            clTestProg.testClass myLib = new clTestProg.testClass();
            myLib.InitControls(groupBox1);

        }
    }
}

Note: the form only has a 2 controls a groupbox with the name groupBox1 and a button with the name buttonTest. The form name is Form1.

Well, for some reason, btnAdd is null so the code's not finding it within the form's Controls collection.

You could try cycling through the collection and printing out the names of the controls to a MessageBox, just to make sure what you've got in there.

The code looks OK to me.

Are you sure that you set the Name property for the Button you're trying to access?