Need to extend existing windows form controls

Question

I have a windows form project and want to extend current windows form controls (checkbox, radio button, and textbox) with custom properties.

First of all is that possible? It seems so, but i'm not 100% on how to properly do that...

I have started to build a second project in my solution which is a DLL project and create custom classes that inherit from the checkbox, radio button and textbox classes. I made a reference to the dll project in my main project, however those controls do not show up in my toolbox when trying to add them to a windows form.

How do i get it where the controls are usable from the toolbox in my windows form project.

Daniel · Answer

Another update: One thing I found to work was to create a user control in the DLL project and change the inheritence from UserControl to the control i am extending (radiobutton etc..) and add the properties i want compile and it shows up in the toolbox in the windows form project. This didn't seem to be the way to do it but it looks like it is working.

Daniel · Answer

An update: I have setup my test solution with two projects (a windows form and dll) but cannot see the components in the toolbox and still get the error message when pointing to the dll file containg them. Is there a way to update the solution to C# Corner for someone to look at???. I am officially stumped at this point. Post you email if you are willing to have a look and i can send you the code.

Daniel · Answer

Great thanks for the good info.! I looks like i am on the right path. I am not sure what the problem is with the controls showing up in the toolbox. I have tried the Add Tab method and get a message that says there are no components in  I am trying to work on that now....

Scott Lysle · Answer

Well it is no big trick to extend an existing control; if you create a new class library project and add classes to it each of which extends an existing control you can reference the resulting DLL into another project and use the controls. Here is a simple example of a custom control; it extends the text box control to only allow it to display currency values: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace CustomControls { /// /// /// Extended textbox control; the purpose of the control is /// to permit the user to enter values as currency /// /// /// public partial class CurrencyTextBox : TextBox { /// /// member variable used to keep dollar value /// private Decimal mDollarValue; /// /// constructor /// public CurrencyTextBox() { InitializeComponent(); DollarValue = 0; } /// /// Default OnPaint /// /// protected override void OnPaint( PaintEventArgs pe) { // Calling the base class OnPaint base .OnPaint(pe); } /// /// Limit user input to numbers decimals and control chars /// /// /// private void CurrencyTextBox_KeyPress( object sender KeyPressEventArgs e) { // allows only numbers decimals and control characters if (! Char .IsNumber(e.KeyChar) && ! Char .IsControl(e.KeyChar) && e.KeyChar != '.' ) { e.Handled = true ; } if (e.KeyChar == '.' && this .Text.Contains( . )) { e.Handled = true ; } if (e.KeyChar == '.' && this .Text.Length { e.Handled = true ; } } /// /// Valid inputs into the control and show as currency /// /// /// private void CurrencyTextBox_Validated( object sender EventArgs e) { try { // format the value as currency Decimal dTmp = Convert .ToDecimal( this .Text); this .Text = dTmp.ToString( C ); } catch { } } /// /// Manange entry into the control whenever it is selected; /// make sure that the dollar value is set and the cursor /// positioned to end of the string /// /// /// private void CurrencyTextBox_Click( object sender EventArgs e) { this .Text = mDollarValue.ToString(); if ( this .Text == 0 ) this .Clear(); this .SelectionStart = this .Text.Length; } /// /// Update the property containing the decimal value; /// this is to support display and edit of value /// after it has been converted to a currency string /// in the application /// /// /// private void CurrencyTextBox_TextChanged( object sender EventArgs e) { try { DollarValue = Convert .ToDecimal( this .Text); } catch { } } /// /// property to maintain value of control /// public decimal DollarValue { get { return mDollarValue; } set { mDollarValue = value ; } } } } As for having the controls show up in the toolbox; if the project is included in the current solution the controls will appear. If you reference the DLL I think you find that you may need to add the controls to the toolbox (Add Tab Choose Items).