Beginner question

Question

I've just begun to learn C# and am trying to create a text box that will accept only integers and backspace key. I've created the code for doing that within the 'KeyPress' event for the text box:

private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)

{

if (!Char.IsDigit(e.KeyChar) && e.KeyChar != (char)8)

{

e.Handled = true;

}

}

I realize that I can use a MaskedTextBox, but my real interest is in trying to understand how to use the above example to better understand OOP. I would like to create a generic method that can be called upon from any number of text boxes and I'm not sure how to do that for a KeyPress event. If someone can provide an example with some explanatory notes, I would greatly appreciate it.

Thank you,

imadman

Scott Lysle · Answer

Create a custom control by extending the textbox; here is an example of a control built to display currency: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace MuControls { /// /// C U R R E N C Y T E X T B O X C O N T R O L /// /// 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 ; } } } }

Scott Lysle · Answer

Create a custom control by extending the textbox; here is an example of a control built to display currency: using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace MuControls { /// /// C U R R E N C Y T E X T B O X C O N T R O L /// /// 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 ; } } } }