Develop Reference

C# if statement to test if value is not a number

I am trying to save the .text of a label to a database but sometimes that label is an infinity symbol. To catch for this I have created an if statement which checks if the label is a number or not and throws a message box up to tell the user. However more often than not the label will be a decimal number and the if statement throws up the message box. I was wondering if anyone could help me out please?
private void btnSaveResults_Click(object sender, EventArgs e)
{
btnClearData.Enabled = true;
if (System.Text.RegularExpressions.Regex.IsMatch(lblAerobicCap.Text, "[^0-9]"))
{
MessageBox.Show("Im sorry, there seems to have been an error in the inputting of the readings, please restart the test");
}
else
{
AthletesDetailsNew users = new AthletesDetailsNew();
DateTime dateTimeVariable = DateTime.Now;
users.Date_Of_Test = dateTimeVariable;
users.First_Name = comboBoxFirstName.Text;
users.Surname = comboBoxNewSurname.Text;
users.Age = int.Parse(comboBoxAge.Text);
users.Account_Number = int.Parse(comboBoxAccountNumber.Text);
users.Aerobic_Capacity = /*Math.Truncate*/(decimal.Parse(lblAerobicCap.Text));
DataClassDataContext dbCtx = new DataClassDataContext();
dbCtx.AthletesDetailsNews.InsertOnSubmit(users);
try
{
dbCtx.SubmitChanges();
MessageBox.Show("Data saved");
}
catch
{
MessageBox.Show("Data failed to save");
}
}
}

You should use the .TryParse() method for this.
for example:
decimal value;
bool isNumber = Decimal.TryParse(inputVariable, out value);

Use decimal.TryParse so in case of success you can reuse the result
decimal aerobicCap = -1;
if (!decimal.TryParse( lblAerobicCap.Text, out aerobicCap))
{
MessageBox.Show("Im sorry, there seems to have been an error in the inputting of the readings, please restart the test");
}
else
{
// code ...
users.Aerobic_Capacity = aerobicCap;

I think you need to trim the spaces from lblAerobicCap.Text prior to checking if the value is a number. Something like lblAerobicCap.Text = lblAerobicCap.Text.Trim().
lblAerobicCap.Text = lblAerobicCap.Text.Trim();
if (System.Text.RegularExpressions.Regex.IsMatch(lblAerobicCap.Text, "[^0-9]"))
{
MessageBox.Show("Im sorry, there seems to have been an error in the inputting of the readings, please restart the test");
}
[ ... ]

Better still avoid users entering anything but numbers. That way you do not have to validate the input.
For the digits use something like this:
void Control_KeyPress(object sender, KeyPressEventArgs e)
{
if (!Char.IsDigit(e.KeyChar))
{
e.Handled = true;
}
}
Decimal:
void Control_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode != Keys.Decimal)
{
e.Handled = true;
}
}

I have used an extension method in the past which works nicely for me:
public static bool IsNumber(this object value)
{
return value is sbyte
|| value is byte
|| value is short
|| value is ushort
|| value is int
|| value is uint
|| value is long
|| value is ulong
|| value is float
|| value is double
|| value is decimal;
}
object testObject = 0.1;
if (testObject.IsNumber()) { MessageBox.Show("Hooray!"); }

Exception Handling C#

I am relatively new at this and have been racking my brain attempting to get my program to work properly and it just won't. I am working in Visual Studio 2012 C# on a Forms Application.
I need it to produce a distinct error message when the user input value is more than 0 but less than 10,000. It also must produce a distinct error message when the user enters a non-numeric value and a distinct error message when the user fails to enter any value at all.
The code I've written so far produces a distinct error message when the user enters a non-numeric value or when they fail to enter any value at all, but it does not trigger an error message when the user enters a value that is below or over the required range.
It is as if the compiler is ignoring the code I've written for the first exception/overflow exception and only recognizing the code for the second and final exception. My code has no coding errors. It appears that my problem is in the logic.
Please help me if you can. My code is below thanks!
private void btnCalculate_Click(object sender, System.EventArgs e)
{
try
{
{
decimal subtotal = Convert.ToDecimal(txtSubtotal.Text);
decimal discountPercent = .25m;
decimal discountAmount = subtotal * discountPercent;
decimal invoiceTotal = subtotal - discountAmount;
lblDiscountPercent.Text = discountPercent.ToString("p1");
lblDiscountAmount.Text = discountAmount.ToString("c");
lblTotal.Text = invoiceTotal.ToString("c");
}
}
catch (OverflowException)
{
decimal subtotal = Convert.ToDecimal(txtSubtotal.Text);
if (subtotal <= 0)
{
MessageBox.Show("Subtotal must be greater than $0.00. ", "Error Entry");
txtSubtotal.Focus();
}
if (subtotal >= 10000)
{
MessageBox.Show("Subtotal must be less than $10000.00. ", "Error Entry");
txtSubtotal.Focus();
}
}
catch (Exception)
{
if (txtSubtotal.Text == "")
{
MessageBox.Show("Subtotal is a required field. ", "Error Entry");
}
else
{
MessageBox.Show(
"Please enter a valid Number for the subtotal field.", "Error Entry");
txtSubtotal.Focus();
}
}
}
private void btnExit_Click(object sender, System.EventArgs e)
{
this.Close();
}
private void txtSubtotal_TextChanged(object sender, EventArgs e)
{
}
}
}

I would used KeyEvent press enter or Leave event for this, first I need to create generic class for verification if the input from the user is not a string.
Condition:
1 verify if the input is not a string Im using generic for general purposes class.
public class iCnF()
{
public static System.Boolean IsNumeric(System.Object Expression)
{
if (Expression == null || Expression is DateTime)
return false;
if (Expression is Int16 || Expression is Int32 || Expression is Int64 || Expression is Decimal || Expression is Single || Expression is Double || Expression is Boolean)
return true;
try
{
if(Expression is string)
Double.Parse(Expression as string);
else
Double.Parse(Expression.ToString());
return true;
} catch {} // just dismiss errors but return false
return false;
}
}
Then I need to verify if the input is not empty
private void txtSubtotal_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter || e.KeyCode == Keys.Tab)
{
if (txtSubtotal.Text.Length > 0)
{
bool sd = iCnF.IsNumeric(txtSubtotal.Text);
if (sd == false)
{
MessageBox.Show("Subtotal must be a numeric value. ", "Error Entry");
txtSubtotal.Clear();
txtSubtotal.Focus();
}
else
{
decimal subtotal = Convert.ToDecimal(txtSubtotal.Text);
if (subtotal <= 0)
{
MessageBox.Show("Subtotal must be greater than $0.00. ", "Error Entry");
txtSubtotal.Focus();
}
if (subtotal >= 10000)
{
MessageBox.Show("Subtotal must be less than $10000.00. ", "Error Entry");
txtSubtotal.Focus();
}
}
}
else
{
MessageBox.Show("Subtotal must not be empty. ", "Error Entry");
txtSubtotal.Focus();
}
}
}
if not empty and numberic value my subtotal <= 0 and subtotal >= 10000
Hope this will help you :D

As I already mentioned in comment you should consider moving your code out of catch block.
In this case you should think of creating a simple method which will validate your input and produces output message.
An example is for you:
private bool IsPageValid()
{
string errorMessage = string.Empty;
bool isValid = true;
if (subtotal <= 0)
{
errorMessage+="<li>"+"<b>Subtotal must be greater than $0.00. ", "Error Entry"+ "</b><br/>";
txtSubtotal.Focus();
isValid=false;
}
}
Likewise write other clause of validations in this function..This will validate each of your condition and if fails it would make the isValid false thus not allowing users to submit.
Now you should call this function in your button click.
protected void btnSubmit_Click(object sender, EventArgs e)
{
ClearMessage();
if (IsPageValid().Equals(true))
{
// allow next action to happen.
}
}

Code should look like this
try {
decimal subtotal = Convert.ToDecimal(txtSubtotal.Text);
try {
if(x<0 || x>10000){
throw new OverFlowException("");
}
//Do what ever you want
}
catch(Exception ex){
// catch overflow
}
}
catch(Exception ex){
// catch nonnumeric value
}

_textChanged event is giving me error "Object reference not set to an instance of an object"

I'm new to C# so still finding my way around.
I have a button I want to enable only when a user enter text to textbox.
I get this error - "Object reference not set to an instance of an object".
Here is the related code (without the using and variables):
public MainWindow()
{
MessageBox.Show("Make sure to edit Settings tab.");
InitializeComponent();
if (startTextBox.Text == "0") // Checks to see if a textbox has some text other than zero. if no than the user cannot press button1 yet.
{
button1.IsEnabled = false;
}
else
{
button1.IsEnabled = true;
}
}
private void Window_Loaded(object sender, RoutedEventArgs e)
{
if (radioButton1.IsChecked == false)
{
label17.Content = "No Hourly wage was set.";
}
}
private void add(object sender, RoutedEventArgs e) /// here is a very long method so I've removed its content.
}
public void printTime()
{
int Sum = (this.EndInt - this.StartInt);
int Money = (Sum * this.L1001);
label16.Content = Sum;
label17.Content = Money;
if ((textBox1.Text == "0") && ((textBox2.Text == "0") || (textBox3.Text == "0")))
{
label17.Content = "No Hourly wage was set.";
}
}
public void printTime2()
{
int Sum = (this.EndInt - this.StartInt);
MessageBox.Show("Is it possible that you've worked - " + Sum + " Hours?");
}
public void printTime3()
{
int Sum = (this.EndInt - this.StartInt);
int Money = (Sum * this.L1001);
label16.Content = Sum;
label17.Content = Money;
if (textBox1.Text == "0")
{
label17.Content = "No Hourly wage was set.";
}
}
public int Convert(String S)
{
int i = int.Parse(S);
return i;
}
// Input Validation For Excepting Integers Only!
private void input(object sender, TextCompositionEventArgs e)
{ CheckIsNumeric(e); }
private void CheckIsNumeric(TextCompositionEventArgs e)
{
int result; if (!(int.TryParse(e.Text, out result) || e.Text == "."))
{ e.Handled = true; MessageBox.Show("Numbers Only"); }
}
private void startTextBox_TextChanged(object sender, TextChangedEventArgs e)
{
button1.IsEnabled = true;
}
}
}

It's the scope problem. You didn't show where button1 is defined. But inside your event handler startTextBox_TextChanged, button1 definition is nowhere to be found (actually it needs to be instantiated as well). Since you try to invoke a method on an object (button1) which has not been instantiated yet, that exception was thrown.
If you post more than just those snippets, either I or someone else might be able to further help you.

C# Textbox validation should only accept integer values, but allows letters as well

if (textBox1.Text != "") // this forces user to enter something
{
// next line is supposed to allow only 0-9 to be entered but should block all...
// ...characters and should block a backspace and a decimal point from being entered....
// ...but it is also allowing characters to be typed in textBox1
if(!IsNumberInRange(KeyCode,48,57) && KeyCode!=8 && KeyCode!=46) // 46 is a "."
{
e.Handled=true;
}
else
{
e.Handled=false;
}
if (KeyCode == 13) // enter key
{
TBI1 = System.Convert.ToInt32(var1); // converts to an int
Console.WriteLine("TBI1 (var1 INT)= {0}", var1);
Console.WriteLine("TBI1= {0}", TBI1);
}
if (KeyCode == 46)
{
MessageBox.Show("Only digits...no dots please!");
e.Handled = !char.IsDigit(e.KeyChar) && !char.IsControl(e.KeyChar);
}
}
else
{
Console.WriteLine("Cannot be empty!");
}
// If I remove the outer if statement and skip checking for an empty string, then
// it prevents letters from being entered in the textbox. I need to do both, prevent an
// empty textbox AND prevent letters from being entered.
// thanks, Sonny5

You didn't specify where this code runs, but my assumption would be it runs on key down. Since key down is received before the character is processed and the Text property is updated, your check for .Text == "" will prevent the rest of the validation running, at least for the first character.
You should move the check for empty value on a different event than the check for the key pressed.

I think you could use the IsDigit function.
Something along these lines:
string textBoxText = "12kj3";
if (!textBoxText.Equals(String.Empty)) // this forces user to enter something
{
foreach (char c in textBoxText.ToArray())
{
if (!Char.IsDigit(c))
{
//return false;
}
}
//return true;
}
else
{
Console.WriteLine("Cannot be empty!");
}
Hope you get the idea.

You can use the following RegEx to check that it is a number "^\d+$" and required.

bool bV=false;
private void textBox1_Validated(object sender, EventArgs e)
{
TextBox textBoxText = sender as TextBox;
if (!textBoxText.Equals(String.Empty))
{
foreach (char c in textBoxText.Text.ToArray())
{
if (!Char.IsDigit(c))
{
if (!bV)
{
MessageBox.Show("Input value not valid plase Insert Integer Value");
bV = true;
textBox1.Text = String.Empty;
break;
}
}
}
}
}
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
bV = false;
}

Not allow zero in textbox

I need a textbox which only the user can permit to enter integers. But the user can't enter zero. i.e, he can enter 10,100 etc. Not 0 alone.
How can I make event in KeyDown?

The way you plan to do this, is very annoying for a user. You're guessing what a user wants to enter, and act upon your guess, but you can be so wrong.
It also has holes, for example, a user can enter "10" and then delete the "1". Or he could paste in a "0" -- you do allow paste, don't you?
So my solution would be: let him enter any digit he likes, any way he likes, and validate the input only after he finished, for example, when the input loses focus.

Why not using a NumericUpDown and make the following settings:
upDown.Minimum = 1;
upDown.Maximum = Decimal.MaxValue;

Use int.TryParse to convert the text into a number and check if that number is not 0. Use the Validating event for the check.
// this goes to you init routine
textBox1.Validating += textBox1_Validating;
// the validation method
private void textBox1_Validating(object sender, CancelEventArgs e)
{
if (textBox1.Text.Length > 0)
{
int result;
if (int.TryParse(textBox1.Text, out result))
{
// number is 0?
e.Cancel = result == 0;
}
else
{
// not a number at all
e.Cancel = true;
}
}
}
EDIT:
Okay, since you use WPF you should take a look at how to implement validation the WPF way. Here is a validation class that implements the above logic:
public class StringNotZeroRule : ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
if (textBox1.Text.Length == 0)
return new ValidationResult(true, null);
int result;
if (int.TryParse(textBox1.Text, out result))
{
// number is 0?
if (result == 0)
{
return new ValidationResult(false, "0 is not allowed");
}
}
else
{
// not a number at all
return new ValidationResult(false, "not a number");
}
return new ValidationResult(true, null);
}
}

This is another variation on the theme:
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
char newChar = Convert.ToChar(e.KeyValue);
if (char.IsControl(newChar))
{
return;
}
int value;
e.SuppressKeyPress = int.TryParse((sender as TextBox).Text + newChar.ToString(), out value) ? value == 0 : true;
}

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (textBox1.Text == "" && e.KeyChar == '0')
{
e.Handled = true;
return;
}
if (e.KeyChar < '0' || e.KeyChar > '9')
{
e.Handled = true;
return;
}
}
not nice but it works