Convert a System.Windows.Input.KeyEventArgs key to a char - c#

I need to get the event args as a char, but when I try casting the Key enum I get completely different letters and symbols than what was passed in.
How do you properly convert the Key to a char?
This is what I've tried
ObserveKeyStroke(this, new ObervableKeyStrokeEvent((char)((KeyEventArgs)e.StagingItem.Input).Key));
Edit: I also don't have the KeyCode property on the args. I'm getting them from the InputManager.Current.PreNotifyInput event.


See How to convert a character in to equivalent System.Windows.Input.Key Enum value?
Use KeyInterop.VirtualKeyFromKey instead.


It takes a little getting used to, but you can just use the key values themselves. If you're trying to limit input to alphanumerics and maybe a little extra, the code below may help.
private bool bLeftShiftKey = false;
private bool bRightShiftKey = false;
private bool IsValidDescriptionKey(Key key)
{
//KEYS ALLOWED REGARDLESS OF SHIFT KEY
//various editing keys
if (
key == Key.Back ||
key == Key.Tab ||
key == Key.Up ||
key == Key.Down ||
key == Key.Left ||
key == Key.Right ||
key == Key.Delete ||
key == Key.Space ||
key == Key.Home ||
key == Key.End
) {
return true;
}
//letters
if (key >= Key.A && key <= Key.Z)
{
return true;
}
//numbers from keypad
if (key >= Key.NumPad0 && key <= Key.NumPad9)
{
return true;
}
//hyphen
if (key == Key.OemMinus)
{
return true;
}
//KEYS ALLOWED CONDITITIONALLY DEPENDING ON SHIFT KEY
if (!bLeftShiftKey && !bRightShiftKey)
{
//numbers from keyboard
if (key >= Key.D0 && key <= Key.D9)
{
return true;
}
}
return false;
}
private void cboDescription_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.LeftShift)
{
bLeftShiftKey = true;
}
if (e.Key == Key.RightShift)
{
bRightShiftKey = true;
}
if (!IsValidDescriptionKey(e.Key))
{
e.Handled = true;
}
}
private void cboDescription_PreviewKeyUp(object sender, KeyEventArgs e)
{
if (e.Key == Key.LeftShift)
{
bLeftShiftKey = false;
}
if (e.Key == Key.RightShift)
{
bRightShiftKey = false;
}
}


That work for me:
Based on the last entry i found that in WPF there is no such event PreNotifyInput, but i found and equivalent PreviewTextInput
First I try with a RegExp, but I cant make it work, then I use a simple indexOf.
private bool ValidChar(string _char)
{
string Lista = #" ! "" # $ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? # A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ";
return Lista.IndexOf(_char.ToUpper()) != -1;
//System.Text.RegularExpressions.Regex RegVal = new System.Text.RegularExpressions.Regex(#"(?<LETRAS>[A-Z]+)+(?<NUMERO>[0-9]+)+(?<CAR>[!|""|#|$|%|&|'|(|)|*|+|,|\-|.|/|:|;|<|=|>|?|#]+)+");
//return RegVal.IsMatch(_char);
}
private void textBoxDescripcion_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
if (!ValidChar(e.Text))
e.Handled = true;
}


I know this is old, but none of the answers seem to actually answer the question. The reason a different char is coming back is because when you just try to cast it to a char you are casting the enum value to a 'char'. However:
var keyPressed = e.key.ToString();
Works great. Returns the key pressed as a string. Then you check the length. If it's == 1 then it's a char, number or symbol. If it's greater than 1 it's a special key.
If you just want the char you can then do keyPressed[0];
This is how I do it.
private void scrollViewer_KeyDown(object sender, KeyEventArgs e)
{
if (!e.IsRepeat)
{
var keyPressed = e.Key.ToString();
if(keyPressed.Length == 1)
CharKeyPressed(keyPressed[0]);
else if(keyPressed.Length > 1)
HandleSpecialKey(keyPressed)
}
}


Inside your PreNotifyInput handler, try something like this:
if (e.StagingItem.Input is System.Windows.Input.TextCompositionEventArgs)
{
if (!String.IsNullOrEmpty((e.StagingItem.Input as System.Windows.Input.TextCompositionEventArgs).Text))
{
Char c = (e.StagingItem.Input as System.Windows.Input.TextCompositionEventArgs).Text[0];
}
}
It raises multiple times for the different routed events, so you may want to filter for a particular one.

Related

Textbox Only Accepts Dot( . ) And Dash( - )

I Tried Some Codes But Didnt Work
For Example
I Found This And It Didnt Work:
if (!char.IsControl(e.KeyChar)
&& !char.IsDigit(e.KeyChar)
&& e.KeyChar != '.')
{
e.Handled = true;
}
// only allow one decimal point
if (e.KeyChar == '.'
&& (sender as TextBox).Text.IndexOf('.') > -1)
{
e.Handled = true;
}

You have a very simple, yet understandable error there.
The Handled property of KeyPressEventArgs should be set to true to keep the operating system from further processing the key.
https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.keypresseventargs?view=netframework-4.8
In other words, set this to true when you want to PREVENT the key.
Therefore, change your code like this to ALLOW further processing when the pressed key fits the conditions.
Please also see how the boolean variables are introduced to make the code readable.
The code below allows
A ( - ) character if it is the first char in the text box
A ( . ) character if it is not the first char and if there are no other dots
Any control characters
And any digits.
Good luck.
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
bool isControl = char.IsControl(e.KeyChar);
bool isDigit = char.IsDigit(e.KeyChar);
bool isDot = e.KeyChar == '.';
bool alreadyHasADot = (sender as TextBox).Text.IndexOf('.') != -1;
bool isHyphen = e.KeyChar == '-';
bool isFirstChar = (sender as TextBox).Text.Length == 0;
bool isAllowed =
isControl ||
isDigit ||
(isDot && !isFirstChar && !alreadyHasADot) ||
(isHyphen && isFirstChar);
if (!isAllowed)
{
e.Handled = true;
}
}

C# TextBox allow minus sign (-) only in the beginning of string

Sorry if this is a really basic question but I'm new to C# and it's my first windows form app.
In the code below my TextBox only accepts a decimal point ",", a minus sign "-", digits, and it also accepts the input of the delete and backspace keys (correct me if I'm wrong). So I can input and delete numbers like:
-12.31
-.31
The problem is I can also input something like:
12-
Is there a way to only input "-" if its the first character of the string? I tried google and I tried to come up with something but nothing seems to work.
And thank you for your time.
private void TextBox_KeyPress(object sender, KeyPressEventArgs e)
{
if (!char.IsDigit(e.KeyChar) && (e.KeyChar != ',') && (e.KeyChar != '-') && (e.KeyChar != (char)8))
{
e.Handled = true;
}
if ((e.KeyChar == ',') && ((sender as TextBox).Text.IndexOf(',') > -1))
{
e.Handled = true;
}
if ((e.KeyChar == '-') && ((sender as TextBox).Text.IndexOf('-') > -1))
{
e.Handled = true;
}
}

You can check where the cursor is by using SelectionStart:
var textBox = (TextBox)sender;
if (e.KeyChar == '-' && (textBox.SelectionStart !=0 || textBox.Text.Contains("-")))
{
e.Handled = true;
}

Check for Key press event in C#

I have a List<System.Windows.Forms.Keys>.
I want to check if all Keys in the list are pressed in a keydown event.
But how?
My method is:
public bool Triggered( string indentifier, KeyEventArgs e )
{
List<Keys> keys = Shortcuts.Keys.First( x => Shortcuts[x].Indentifier == indentifier );
keys.Reverse();
foreach( Keys key in keys )
{
if ( e.KeyCode != key )
return false;
}
return true;
}
Getting the keys works but the check don't.

Answer to your question Why is e.KeyCode the same key every time but when I do if ( e.KeyCode == Keys.Control && e.KeyCode == Keys.S ) because it is a flag enum (answer for detailed explanation).
you can do is change your code to :
List<Keys> keys = Shortcuts.Keys.First( x => Shortcuts[x].Indentifier == indentifier );
keys.Reverse();
Keys allKey = Keys.None;
keys.ForEach(ele => allKey |= ele);
return (e.KeyData == allKey);

How to make a xaml textbox in silverlight accept only numbers with maximum one decimal point precision

How to make a xaml textbox in silverlight accept only numbers with maximum one decimal point precison. I have tried the answers in this question How to make a textBox accept only Numbers and just one decimal point in Windows 8. But it did not work. How can I do this ?

You can write a function like this,
txtDiscount.KeyDown += new KeyEventHandler(EnsureNumbers);
//Method to allow only numbers,
void EnsureNumbers(object sender, KeyEventArgs e)
{
if (e.Key == Key.Tab)
{
return;
}
bool result = EnsureDecimalPlaces();
if (result == false)
{
var thisKeyStr = "";
if (e.PlatformKeyCode == 190 || e.PlatformKeyCode == 110)
{
thisKeyStr = ".";
}
else
{
thisKeyStr = e.Key.ToString().Replace("D", "").Replace("NumPad", "");
}
var s = (sender as TextBox).Text + thisKeyStr;
var rStr = "^[0-9]+[.]?[0-9]*$";
var r = new Regex(rStr, RegexOptions.IgnoreCase);
e.Handled = !r.IsMatch(s);
}
else
{
e.Handled = true;
}
}
Method to ensure only 1 decimal,
bool EnsureDecimalPlaces()
{
string inText = txtDiscount.Text;
int decPointIndex = inText.IndexOf('.');
if (decPointIndex < 1 || decPointIndex == 1)
{
return false;
}
else
return true;
}

Numeric Data Entry in WPF

How are you handling the entry of numeric values in WPF applications?
Without a NumericUpDown control, I've been using a TextBox and handling its PreviewKeyDown event with the code below, but it's pretty ugly.
Has anyone found a more graceful way to get numeric data from the user without relying on a third-party control?
private void NumericEditPreviewKeyDown(object sender, KeyEventArgs e)
{
bool isNumPadNumeric = (e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9) || e.Key == Key.Decimal;
bool isNumeric = (e.Key >= Key.D0 && e.Key <= Key.D9) || e.Key == Key.OemPeriod;
if ((isNumeric || isNumPadNumeric) && Keyboard.Modifiers != ModifierKeys.None)
{
e.Handled = true;
return;
}
bool isControl = ((Keyboard.Modifiers != ModifierKeys.None && Keyboard.Modifiers != ModifierKeys.Shift)
|| e.Key == Key.Back || e.Key == Key.Delete || e.Key == Key.Insert
|| e.Key == Key.Down || e.Key == Key.Left || e.Key == Key.Right || e.Key == Key.Up
|| e.Key == Key.Tab
|| e.Key == Key.PageDown || e.Key == Key.PageUp
|| e.Key == Key.Enter || e.Key == Key.Return || e.Key == Key.Escape
|| e.Key == Key.Home || e.Key == Key.End);
e.Handled = !isControl && !isNumeric && !isNumPadNumeric;
}

How about:
protected override void OnPreviewTextInput(System.Windows.Input.TextCompositionEventArgs e)
{
e.Handled = !AreAllValidNumericChars(e.Text);
base.OnPreviewTextInput(e);
}
private bool AreAllValidNumericChars(string str)
{
foreach(char c in str)
{
if(!Char.IsNumber(c)) return false;
}
return true;
}

This is how I do it. It uses a regular expression to check if the text that will be in the box is numeric or not.
Regex NumEx = new Regex(#"^-?\d*\.?\d*$");
private void TextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
if (sender is TextBox)
{
string text = (sender as TextBox).Text + e.Text;
e.Handled = !NumEx.IsMatch(text);
}
else
throw new NotImplementedException("TextBox_PreviewTextInput Can only Handle TextBoxes");
}
There is now a much better way to do this in WPF and Silverlight. If your control is bound to a property, all you have to do is change your binding statement a bit. Use the following for your binding:
<TextBox Text="{Binding Number, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"/>
Note that you can use this on custom properties too, all you have to do is throw an exception if the value in the box is invalid and the control will get highlighted with a red border. If you click on the upper right of the red border then the exception message will pop up.

I've been using an attached property to allow the user to use the up and down keys to change the values in the text box. To use it, you just use
<TextBox local:TextBoxNumbers.SingleDelta="1">100</TextBox>
This doesn't actually address the validation issues that are referred to in this question, but it addresses what I do about not having a numeric up/down control. Using it for a little bit, I think I might actually like it better than the old numeric up/down control.
The code isn't perfect, but it handles the cases I needed it to handle:
Up arrow, Down arrow
Shift + Up arrow, Shift + Down arrow
Page Up, Page Down
Binding Converter on the text property
Code behind
using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
namespace Helpers
{
public class TextBoxNumbers
{
public static Decimal GetSingleDelta(DependencyObject obj)
{
return (Decimal)obj.GetValue(SingleDeltaProperty);
}
public static void SetSingleDelta(DependencyObject obj, Decimal value)
{
obj.SetValue(SingleDeltaProperty, value);
}
// Using a DependencyProperty as the backing store for SingleValue. This enables animation, styling, binding, etc...
public static readonly DependencyProperty SingleDeltaProperty =
DependencyProperty.RegisterAttached("SingleDelta", typeof(Decimal), typeof(TextBoxNumbers), new UIPropertyMetadata(0.0m, new PropertyChangedCallback(f)));
public static void f(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
TextBox t = o as TextBox;
if (t == null)
return;
t.PreviewKeyDown += new System.Windows.Input.KeyEventHandler(t_PreviewKeyDown);
}
private static Decimal GetSingleValue(DependencyObject obj)
{
return GetSingleDelta(obj);
}
private static Decimal GetDoubleValue(DependencyObject obj)
{
return GetSingleValue(obj) * 10;
}
private static Decimal GetTripleValue(DependencyObject obj)
{
return GetSingleValue(obj) * 100;
}
static void t_PreviewKeyDown(object sender, System.Windows.Input.KeyEventArgs e)
{
TextBox t = sender as TextBox;
Decimal i;
if (t == null)
return;
if (!Decimal.TryParse(t.Text, out i))
return;
switch (e.Key)
{
case System.Windows.Input.Key.Up:
if (Keyboard.Modifiers == ModifierKeys.Shift)
i += GetDoubleValue(t);
else
i += GetSingleValue(t);
break;
case System.Windows.Input.Key.Down:
if (Keyboard.Modifiers == ModifierKeys.Shift)
i -= GetDoubleValue(t);
else
i -= GetSingleValue(t);
break;
case System.Windows.Input.Key.PageUp:
i += GetTripleValue(t);
break;
case System.Windows.Input.Key.PageDown:
i -= GetTripleValue(t);
break;
default:
return;
}
if (BindingOperations.IsDataBound(t, TextBox.TextProperty))
{
try
{
Binding binding = BindingOperations.GetBinding(t, TextBox.TextProperty);
t.Text = (string)binding.Converter.Convert(i, null, binding.ConverterParameter, binding.ConverterCulture);
}
catch
{
t.Text = i.ToString();
}
}
else
t.Text = i.ToString();
}
}
}

I decided to simplify the reply marked as the answer on here to basically 2 lines using a LINQ expression.
e.Handled = !e.Text.All(Char.IsNumber);
base.OnPreviewTextInput(e);

Why don't you just try using the KeyDown event rather than the PreviewKeyDown Event. You can stop the invalid characters there, but all the control characters are accepted. This seems to work for me:
private void NumericKeyDown(object sender, System.Windows.Input.KeyEventArgs e)
{
bool isNumPadNumeric = (e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9);
bool isNumeric =((e.Key >= Key.D0 && e.Key <= Key.D9) && (e.KeyboardDevice.Modifiers == ModifierKeys.None));
bool isDecimal = ((e.Key == Key.OemPeriod || e.Key == Key.Decimal) && (((TextBox)sender).Text.IndexOf('.') < 0));
e.Handled = !(isNumPadNumeric || isNumeric || isDecimal);
}

I use a custom ValidationRule to check if text is numeric.
public class DoubleValidation : ValidationRule
{
public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
{
if (value is string)
{
double number;
if (!Double.TryParse((value as string), out number))
return new ValidationResult(false, "Please enter a valid number");
}
return ValidationResult.ValidResult;
}
Then when I bind a TextBox to a numeric property, I add the new custom class to the Binding.ValidationRules collection. In the example below the validation rule is checked everytime the TextBox.Text changes.
<TextBox>
<TextBox.Text>
<Binding Path="MyNumericProperty" UpdateSourceTrigger="PropertyChanged">
<Binding.ValidationRules>
<local:DoubleValidation/>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>

public class NumericTextBox : TextBox
{
public NumericTextBox()
: base()
{
DataObject.AddPastingHandler(this, new DataObjectPastingEventHandler(CheckPasteFormat));
}
private Boolean CheckFormat(string text)
{
short val;
return Int16.TryParse(text, out val);
}
private void CheckPasteFormat(object sender, DataObjectPastingEventArgs e)
{
var isText = e.SourceDataObject.GetDataPresent(System.Windows.DataFormats.Text, true);
if (isText)
{
var text = e.SourceDataObject.GetData(DataFormats.Text) as string;
if (CheckFormat(text))
{
return;
}
}
e.CancelCommand();
}
protected override void OnPreviewTextInput(System.Windows.Input.TextCompositionEventArgs e)
{
if (!CheckFormat(e.Text))
{
e.Handled = true;
}
else
{
base.OnPreviewTextInput(e);
}
}
}
Additionally you may customize the parsing behavior by providing appropriate dependency properties.

Combining the ideas from a few of these answers, I have created a NumericTextBox that
Handles decimals
Does some basic validation to ensure any entered '-' or '.' is valid
Handles pasted values
Please feel free to update if you can think of any other logic that should be included.
public class NumericTextBox : TextBox
{
public NumericTextBox()
{
DataObject.AddPastingHandler(this, OnPaste);
}
private void OnPaste(object sender, DataObjectPastingEventArgs dataObjectPastingEventArgs)
{
var isText = dataObjectPastingEventArgs.SourceDataObject.GetDataPresent(System.Windows.DataFormats.Text, true);
if (isText)
{
var text = dataObjectPastingEventArgs.SourceDataObject.GetData(DataFormats.Text) as string;
if (IsTextValid(text))
{
return;
}
}
dataObjectPastingEventArgs.CancelCommand();
}
private bool IsTextValid(string enteredText)
{
if (!enteredText.All(c => Char.IsNumber(c) || c == '.' || c == '-'))
{
return false;
}
//We only validation against unselected text since the selected text will be replaced by the entered text
var unselectedText = this.Text.Remove(SelectionStart, SelectionLength);
if (enteredText == "." && unselectedText.Contains("."))
{
return false;
}
if (enteredText == "-" && unselectedText.Length > 0)
{
return false;
}
return true;
}
protected override void OnPreviewTextInput(System.Windows.Input.TextCompositionEventArgs e)
{
e.Handled = !IsTextValid(e.Text);
base.OnPreviewTextInput(e);
}
}

You can also try using data validation if users commit data before you use it. Doing that I found was fairly simple and cleaner than fiddling about with keys.
Otherwise, you could always disable Paste too!

My Version of Arcturus answer, can change the convert method used to work with int / uint / decimal / byte (for colours) or any other numeric format you care to use, also works with copy / paste
protected override void OnPreviewTextInput( System.Windows.Input.TextCompositionEventArgs e )
{
try
{
if ( String.IsNullOrEmpty( SelectedText ) )
{
Convert.ToDecimal( this.Text.Insert( this.CaretIndex, e.Text ) );
}
else
{
Convert.ToDecimal( this.Text.Remove( this.SelectionStart, this.SelectionLength ).Insert( this.SelectionStart, e.Text ) );
}
}
catch
{
// mark as handled if cannot convert string to decimal
e.Handled = true;
}
base.OnPreviewTextInput( e );
}
N.B. Untested code.

Add this to the main solution to make sure the the binding is updated to zero when the textbox is cleared.
protected override void OnPreviewKeyUp(System.Windows.Input.KeyEventArgs e)
{
base.OnPreviewKeyUp(e);
if (BindingOperations.IsDataBound(this, TextBox.TextProperty))
{
if (this.Text.Length == 0)
{
this.SetValue(TextBox.TextProperty, "0");
this.SelectAll();
}
}
}

Call me crazy, but why not put plus and minus buttons at either side of the TextBox control and simply prevent the TextBox from receiving cursor focus, thereby creating your own cheap NumericUpDown control?

private void txtNumericValue_PreviewKeyDown(object sender, KeyEventArgs e)
{
KeyConverter converter = new KeyConverter();
string key = converter.ConvertToString(e.Key);
if (key != null && key.Length == 1)
{
e.Handled = Char.IsDigit(key[0]) == false;
}
}
This is the easiest technique I've found to accomplish this. The down side is that the context menu of the TextBox still allows non-numerics via Paste. To resolve this quickly I simply added the attribute/property: ContextMenu="{x:Null}" to the TextBox thereby disabling it. Not ideal but for my scenario it will suffice.
Obviously you could add a few more keys/chars in the test to include additional acceptable values (e.g. '.', '$' etc...)

Private Sub Value1TextBox_PreviewTextInput(ByVal sender As Object, ByVal e As TextCompositionEventArgs) Handles Value1TextBox.PreviewTextInput
Try
If Not IsNumeric(e.Text) Then
e.Handled = True
End If
Catch ex As Exception
End Try
End Sub
Worked for me.

Can you not just use something like the following?
int numericValue = 0;
if (false == int.TryParse(yourInput, out numericValue))
{
// handle non-numeric input
}

void PreviewTextInputHandler(object sender, TextCompositionEventArgs e)
{
string sVal = e.Text;
int val = 0;
if (sVal != null && sVal.Length > 0)
{
if (int.TryParse(sVal, out val))
{
e.Handled = false;
}
else
{
e.Handled = true;
}
}
}

Can also use a converter like:
public class IntegerFormatConverter : IValueConverter
{
public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
int result;
int.TryParse(value.ToString(), out result);
return result;
}
public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
int result;
int.TryParse(value.ToString(), out result);
return result;
}
}

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