Can someone explain how to use TryParse in C# Visual Studio to validate some textbox. I need a function using TryParse, I have an idea but it's not working
public void Letra(TextBox caja)
{
char valor;
if(char.TryParse(caja.Text, out valor))
{
if (caja.TextLength>1)
{
caja.Text = caja.Text.Remove(caja.TextLength);
caja.SelectionStart = caja.TextLength;
}
}
}
Please see the code below.
Please note, using Javascript this could be done a lot better, but since you really want a C# function, here it is.
public bool isValid(TextBox caja)
{
string sTemp;
if (caja != null)
{
sTemp = caja.Text;
}
else
{
return false;
}
if (sTemp.Length > 0)
{
foreach (char cTemp in sTemp)
{
if (char.IsNumber(cTemp))
{
return false;
}
}
}
else
{
return false;
}
return true;
}
Regards
You can always use Regular Expression for such type of validation. It is best practice and pretty fast-
Regex charOnly=new Regex("^[^0-9]$");
You can use it in C# as you want and if your TestBox is in web form then use RegularExpressionValidator. You should refer How can I get a regex to check that a string only contains alpha characters [a-z] or [A-Z]?
You can check if your string contains numbers with following method
private bool CheckIfTextContainsNumber(string TextToCheck)
{
return Regex.IsMatch(TextToCheck, #"\d");
}
\d stands for digit (0-9) + other digits e.g. arabic
Further you code create a textbox in which you cannot type in kind of numbers by creating an EventHandler which catches the KeyPress-Event.
YourTextBoxControl.KeyPress += YourTextBoxControl_KeyPress;
Here you can check whether the char typed in is a number. If the char is a number then you set Handled to true
private void YourTextBoxControl_KeyPress(object sender, KeyPressEventArgs e)
{
e.Handled = Char.IsNumber(e.KeyChar);
}
Related
I am creating an application that has an entry. I am trying to restrict the entry to only allow for numeric input. I have already tried using Keyboard = "Numeric". For the iPad, however, the keyboard has more characters than just numbers. So I had to restrict what is entered. When I do this however, if the user types in a parenthesis, for example, it does stop the character from being entered. But then if the user presses undo, it crashes. I assume this is because the software keyboard is separate from the app, so it is looking for that parenthesis character, but it isn't there. Here is my code:
private void Entry_TextChanged(object sender, TextChangedEventArgs e)
{
Entry theEntry = (Entry)sender;
string entryText = theEntry.Text;
if(entryText != null && entryText.Length != 0)
{
char theMostRecentInput = entryText[entryText.Length - 1];
if(!Extension.IsNumeric(theMostRecentInput))
{
theEntry.TextChanged -= Entry_TextChanged;
theEntry.Text = e.OldTextValue;
theEntry.TextChanged += Entry_TextChanged;
}
}
}
Thanks for the help!
This issue will occur when Validation like special character, Max Limit, etc... for Input field are implemented.
By that time undo action will have extra character count than current input field text characters length in iOS ShouldChangeCharacters Delegate. This leads to app crash.
One of the solution is to return as false in such scenario instead of disabling undo buttons. Below solution worked for me.
public class ExtEntryRenderer : EntryRenderer
{
protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
base.OnElementPropertyChanged(sender, e);
if (Control != null)
{
Control.ShouldChangeCharacters += (UITextField textField, NSRange range, string replacementString) =>
{
if (range.Location + range.Length > ((UITextField)textField).Text.Length)
return false;
return true;
};
}
}
}
I would do this in a Entry custom renderer that way you you can control the input via ShouldChangeCharacters and not have to kludge it by allowing the input and then having to remove the handler and change the text back to the old value...
Here is a quick example that allows numeric, It also automatically handles clipboard pasting non-numeric strings as those would be disallowed. I am using the NSCharacterSet.DecimalDigits character set as that would be internationalized by the OS, but you could allow/disallow any chars of your choosing.
You could also include haptic, visual or audio feedback on the disallowed/rejected entries...
[assembly: ExportRenderer(typeof(NumericEntry), typeof(NumericEntryRenderer))]
namespace Forms_PCL_Tester.iOS
{
public class NumericEntryRenderer : EntryRenderer
{
protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Entry> e)
{
base.OnElementChanged(e);
if (e.NewElement != e.OldElement)
if (Control != null)
{
Control.KeyboardType = UIKeyboardType.NumbersAndPunctuation;
Control.ShouldChangeCharacters += (UITextField textField, NSRange range, string replacementString) =>
{
foreach (var aChar in replacementString)
if (!NSCharacterSet.DecimalDigits.Contains(aChar))
return false;
return true;
};
}
}
}
}
I have this function of which works fine however is there and easier way to complete the validation check using the mail address class, and would it be more fitting. Thanks in advance.
TextBox tb = new TextBox();
tb.KeyDown += new KeyEventHandler(txtEmail_KeyDown);
string strRegex = #"^(?("")("".+?(?<!\\)""#)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])#))" + #"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-\w]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))";
Regex re = new Regex(strRegex); // New regex Object created
// Run Checks after the enter is pressed.
if (e.KeyCode == (Keys.Enter))
{
// checks for is match, if empty and length
if (!re.IsMatch(txtEmail.Text) || (txtEmail.Text.Equals("")) || txtEmail.Text.Length > 100)
{
// display messagebox with error
MessageBox.Show("Email not correct format!!!! ");
}
else
{
MessageBox.Show("Email Format is correct");
}
}
}
you can validate with the EmailAddressAttribute class pretty easily like this in c#
public bool ValidateEmail(string EmailToVerify)
{
if (new EmailAddressAttribute().IsValid(EmailToVerify))
return true;
else
return false;
}
but to use this you need to add this using at the top of your c# code page
using System.ComponentModel.DataAnnotations;
the only downside to this is that EmailAdressAttribute is not so permisive so it depends on what you want to restrict and permit
And if you need it here is the link the the msdn doc about this class :
https://msdn.microsoft.com/fr-fr/library/system.componentmodel.dataannotations.emailaddressattribute(v=vs.110).aspx
No, it is not stable. Since any regular expression of itself represents a finite state machine, it can, in special cases, get into an infinite loop that grafts to the server's DDOS attack.
Just use MailAddress class for validation.
UPDATE 1
After testing MailAddress class and new EmailAddressAttribute().IsValid("MAIL_TEXT_HERE")
I came to conclusion that EmailAddressAttribute's Validation is working better.
You can implement it in this way, let's say that you have TextBox and Button for submit. Just add this Click event handler to buttons Click Event:
private void button1_Click(object sender, EventArgs e)
{
if(!new EmailAddressAttribute().IsValid(textBox1.Text))
{
MessageBox.Show("Email is not valid");
}
else
{
MessageBox.Show("Email is valid");
}
}
I've found different help through this website but still can't seem to convert a string to int. I've tried many different ways. Here are two of them. On button_click I need to read the textboxes and convert them to int so I can perform standard logic on them. (a > b functions). Below the first section is what I'm using to force the use of numbers during entry into the text boxes.
private void write_button_Click(object sender, EventArgs e)
{
int mat_od1 = int.Parse(matod_box.Text); //Input string in wrong format.
int mat_id1 = int.Parse(matid_box.Text);
int fod1 = int.Parse(fod_box.Text);
int fid1 = int.Parse(fid_box.Text);
int hp1 = int.Parse(hp_box.Text);
//This next section is just to show something else I've tried.
decimal mat_od = Convert.ToDecimal(matod_box.Text); //Same error.
decimal mat_id = Convert.ToDecimal(matid_box.Text);
decimal fod = Convert.ToDecimal(fod_box.Text);
decimal fid = Convert.ToDecimal(fid_box.Text);
decimal hp = Convert.ToDecimal(hp_box.Text);
decimal pass_od = mat_od;
}
private void fod_box_TextChanged(object sender, EventArgs e)
{
try
{
int numinput = int.Parse(fod_box.Text);
if (numinput < 1 || numinput > 500)
{
MessageBox.Show("You must enter a number between 0 and 500.");
}
}
catch (FormatException)
{
MessageBox.Show("You need to enter a number.");
fod_box.Clear();
}
Any help would be appreciated.
instead of int.Parse() you should use int.TryParse(string,out int)
this way you would be able to chek the output and decide wether the string was correctly parsed or not
int i;string s="";
if(int.TryParse(s,out i))
{
//use i
}
else
{
//show error
}
The int.parse conversion should work, as in this sample:
string s = "111";
int i;
if (int.TryParse(s, out i))
{
Console.Write(i);
}
else
{
Console.Write("conversion failed");
}
Are you sure you actually provide legal input for your ints? In any case, you should use TryParse like I did in my sample. Theres no need to use try..catch where you can use boolean methods provided by the framework, which will get you the same result..
All depends on what you are allowing to be put in the text box.
If it might not be a string that can be converted to an integer, including blank, then something like
int value;
if (int.TryParse(SomeString, out value)
{
// it is an int
}
else
{
// it's not an int, so do nothing raise a message or some such.
}
In addition to using Int32.TryParse in the button Click event handler as others have pointed out, you need to be careful what you're doing in the TextBox Changed event handler. You're code here is flawed:
private void fod_box_TextChanged(object sender, EventArgs e)
{
try
{
int numinput = int.Parse(fod_box.Text);
...
}
catch (FormatException)
{
MessageBox.Show("You need to enter a number.");
fod_box.Clear();
}
Calling foo_box.Clear() will clear any text from the textbox, calling the TextChanged handler to be executed again (unless the TextBox was already empty). So if you enter a non-numeric value, your message box will be displayed twice - the first time when it attempts to parse your non-numeric value, the second time when it attempts to parse an empty string as a result of the call to Clear().
In general, I'd avoid doing validation in the Changed event handler.
I need to create a WinForms textbox that allows decimal text exclusive-or integer text. Also, I don't wish to be required to specify the length of the text in the mask; the user should be able to enter as many characters as he wants, as long as the text fits the decimal or integer mold. However, the MaskedTextBox doesn't allow variable-length masking, as far as I know; I can't find a pre-existing control that does this, either.
Advice? I suppose I could inherit TextBox, override OnKeyPress and do the work there, but I don't know whether a pre-existing control would do things more gracefully.
the NumericUpDown control has some built in decimal/integer parsing behavior - sounds like it might be what you're looking for. Of course, you end up with the updown controls on the text box too.
Try this:
private void TextBox1_Validating(object sender, EventArgs e)
{
string expression = "^\d{1,8}(\.\d{2,2})?$";
if (System.Text.RegularExpressions.Regex.Match(this.txt_monto_total.Text, expression).Success)
this.label_total.Visible = false;
else
this.label_total.Visible = true;
}
It's not a mask but it will let you tell the user if they have entered an incorrect format (i do it by showing the label), you can use any regular expression, in my case i only want numbers with 1 or 8 digits before the "." and 2 after it.
Here's a solution. It's not perfect - it may eat control characters in certain cases, and it doesn't cleanly handle pasting - but it works well enough!
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;
namespace WinFormsTest
{
public partial class MaskedTextBox : TextBox
{
public enum EntryTypeEnum
{
Any,
Integer,
Decimal
}
[DefaultValue(EntryTypeEnum.Any)]
public EntryTypeEnum EntryType { get; set; }
public MaskedTextBox()
{
InitializeComponent();
}
protected override void OnKeyPress(KeyPressEventArgs e)
{
var keyIsValid =
(EntryType == EntryTypeEnum.Any)
|| char.IsControl(e.KeyChar)
|| isValid(Text + e.KeyChar);
e.Handled = !keyIsValid;
base.OnKeyPress(e);
}
protected override void OnValidating(CancelEventArgs e)
{
e.Cancel = !isValid(Text);
base.OnValidating(e);
}
protected bool isValid(string textToValidate)
{
switch (EntryType)
{
case EntryTypeEnum.Any:
break;
case EntryTypeEnum.Decimal:
{
decimal result;
if (!decimal.TryParse(textToValidate, out result))
{
return false;
}
}
break;
case EntryTypeEnum.Integer:
{
int result;
if (!int.TryParse(textToValidate, out result))
{
return false;
}
}
break;
}
return true;
}
}
}
After much searching I was able to discover a control on codeproject that allows for a variable length number.
It is the Nullable Masked Edit, and a Better Masked Edit Also! project.
Note you need to use the 'EditMask' field to set the Mask properties. Trying to set the 'Mask' field won't work.
I was able to set a mask of 999.9 and then entering 1.1 would work without having to add leading spaces.
I am a MFC programmer who is new to C# and am looking for a simple control that will allow number entry and range validation.
Look at the "NumericUpDown" control. It has range validation, the input will always be numeric, and it has those nifty increment/decrement buttons.
I had to implement a Control which only accepted numbers, integers or reals.
I build the control as a specialization of (read: derived from) TextBox control, and using input control and a regular expresión for the validation.
Adding range validation is terribly easy.
This is the code for building the regex. _numericSeparation is a string with characters accepted as decimal comma values
(for example, a '.' or a ',': $10.50 10,50€
private string ComputeRegexPattern()
{
StringBuilder builder = new StringBuilder();
if (this._forcePositives)
{
builder.Append("([+]|[-])?");
}
builder.Append(#"[\d]*((");
if (!this._useIntegers)
{
for (int i = 0; i < this._numericSeparator.Length; i++)
{
builder.Append("[").Append(this._numericSeparator[i]).Append("]");
if ((this._numericSeparator.Length > 0) && (i != (this._numericSeparator.Length - 1)))
{
builder.Append("|");
}
}
}
builder.Append(#")[\d]*)?");
return builder.ToString();
}
The regular expression matches any number (i.e. any string with numeric characters) with only one character as a numeric separation, and a '+' or a '-' optional character at the beginning of the string.
Once you create the regex (when instanciating the Control), you check if the value is correct overriding the OnValidating method.
CheckValidNumber() just applies the Regex to the introduced text. If the regex match fails, activates an error provider with an specified error (set with ValidationError public property) and raises a ValidationError event.
Here you could do the verification to know if the number is in the requiered range.
private bool CheckValidNumber()
{
if (Regex.Match(this.Text, this.RegexPattern).Value != this.Text)
{
this._errorProvider.SetError(this, this.ValidationError);
return false;
}
this._errorProvider.Clear();
return true;
}
protected override void OnValidating(CancelEventArgs e)
{
bool flag = this.CheckValidNumber();
if (!flag)
{
e.Cancel = true;
this.Text = "0";
}
base.OnValidating(e);
if (!flag)
{
this.ValidationFail(this, EventArgs.Empty);
}
}
As I said, i also prevent the user from input data in the text box other than numeric characteres overriding the OnKeyPress methdod:
protected override void OnKeyPress(KeyPressEventArgs e)
{
if ((!char.IsDigit(e.KeyChar) && !char.IsControl(e.KeyChar)) && (!this._numberSymbols.Contains(e.KeyChar.ToString()) && !this._numericSeparator.Contains(e.KeyChar.ToString())))
{
e.Handled = true;
}
if (this._numberSymbols.Contains(e.KeyChar.ToString()) && !this._forcePositives)
{
e.Handled = true;
}
if (this._numericSeparator.Contains(e.KeyChar.ToString()) && this._useIntegers)
{
e.Handled = true;
}
base.OnKeyPress(e);
}
The elegant touch: I check if the number valid every time the user releases a key, so the user can get feedback as he/she types. (But remember that you must be carefull with the ValidationFail event ;))
protected override void OnKeyUp(KeyEventArgs e)
{
this.CheckValidNumber();
base.OnKeyUp(e);
}
You can use a regular textbox and a Validator control to control input.
Try using an error provider control to validate the textbox. You can use int.TryParse() or double.TryParse() to check if it's numeric and then validate the range.
You can use a combination of the RequiredFieldValidator and CompareValidator (Set to DataTypeCheck for the operator and Type set to Integer)
That will get it with a normal textbox if you would like, otherwise the recommendation above is good.