How to access an object property from another class?

Question

I have a form with a groupbox but is initializing its controls from another class. along with the controls is a button with its event declared in the initializing class. Now I need to access the properties of the buttons that is programmatically initialized. I use these commands:

private void buttonUniAdd_Click(object sender, EventArgs e)

{

myProg.Misc frmMisc = (myProg.Misc)System.Windows.Forms.Application.OpenForms["Misc"];

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

btnAdd.Text = "&Cancel"; //<-- exception during runtime

}

unfortunately this causes the exception "Object reference not set to an instance of an object.". These are all inside the initialization class that I made.

Mark Gutierrez · Answer

I finally got the problem the btnAdd is indeed null since I forgot that this button is inside the groupbox. I should have used: System.Windows.Forms. Button btnAdd = (System.Windows.Forms. Button )frmMisc.Controls[ groupBox1 ].Controls[ buttonOAdd ]; Now it works. Thanks

Alan · Answer

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; }

Mark Gutierrez · Answer

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.

Alan · Answer

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.

Mark Gutierrez · Answer

Yes I am sure that I have the Name correctly since I copy and paste it from its initialization. But my problem is still the exception that it throws whenever I try to access the property of the button.

Alan · Answer

The code looks OK to me. Are you sure that you set the Name property for the Button you're trying to access?