WPF TextBox to enter decimal values
Solution 1:
I currently use this behavior for digital and decimal input:
public class TextBoxInputBehavior : Behavior<TextBox>
{
const NumberStyles validNumberStyles = NumberStyles.AllowDecimalPoint |
NumberStyles.AllowThousands |
NumberStyles.AllowLeadingSign;
public TextBoxInputBehavior()
{
this.InputMode = TextBoxInputMode.None;
this.JustPositivDecimalInput = false;
}
public TextBoxInputMode InputMode { get; set; }
public static readonly DependencyProperty JustPositivDecimalInputProperty =
DependencyProperty.Register("JustPositivDecimalInput", typeof(bool),
typeof(TextBoxInputBehavior), new FrameworkPropertyMetadata(false));
public bool JustPositivDecimalInput
{
get { return (bool)GetValue(JustPositivDecimalInputProperty); }
set { SetValue(JustPositivDecimalInputProperty, value); }
}
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.PreviewTextInput += AssociatedObjectPreviewTextInput;
AssociatedObject.PreviewKeyDown += AssociatedObjectPreviewKeyDown;
DataObject.AddPastingHandler(AssociatedObject, Pasting);
}
protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.PreviewTextInput -= AssociatedObjectPreviewTextInput;
AssociatedObject.PreviewKeyDown -= AssociatedObjectPreviewKeyDown;
DataObject.RemovePastingHandler(AssociatedObject, Pasting);
}
private void Pasting(object sender, DataObjectPastingEventArgs e)
{
if (e.DataObject.GetDataPresent(typeof(string)))
{
var pastedText = (string)e.DataObject.GetData(typeof(string));
if (!this.IsValidInput(this.GetText(pastedText)))
{
System.Media.SystemSounds.Beep.Play();
e.CancelCommand();
}
}
else
{
System.Media.SystemSounds.Beep.Play();
e.CancelCommand();
}
}
private void AssociatedObjectPreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Space)
{
if (!this.IsValidInput(this.GetText(" ")))
{
System.Media.SystemSounds.Beep.Play();
e.Handled = true;
}
}
}
private void AssociatedObjectPreviewTextInput(object sender, TextCompositionEventArgs e)
{
if (!this.IsValidInput(this.GetText(e.Text)))
{
System.Media.SystemSounds.Beep.Play();
e.Handled = true;
}
}
private string GetText(string input)
{
var txt = this.AssociatedObject;
int selectionStart = txt.SelectionStart;
if (txt.Text.Length < selectionStart)
selectionStart = txt.Text.Length;
int selectionLength = txt.SelectionLength;
if (txt.Text.Length < selectionStart + selectionLength)
selectionLength = txt.Text.Length - selectionStart;
var realtext = txt.Text.Remove(selectionStart, selectionLength);
int caretIndex = txt.CaretIndex;
if (realtext.Length < caretIndex)
caretIndex = realtext.Length;
var newtext = realtext.Insert(caretIndex, input);
return newtext;
}
private bool IsValidInput(string input)
{
switch (InputMode)
{
case TextBoxInputMode.None:
return true;
case TextBoxInputMode.DigitInput:
return CheckIsDigit(input);
case TextBoxInputMode.DecimalInput:
decimal d;
//wen mehr als ein Komma
if (input.ToCharArray().Where(x => x == ',').Count() > 1)
return false;
if (input.Contains("-"))
{
if (this.JustPositivDecimalInput)
return false;
if (input.IndexOf("-",StringComparison.Ordinal) > 0)
return false;
if(input.ToCharArray().Count(x=>x=='-') > 1)
return false;
//minus einmal am anfang zulässig
if (input.Length == 1)
return true;
}
var result = decimal.TryParse(input, validNumberStyles, CultureInfo.CurrentCulture, out d);
return result;
default: throw new ArgumentException("Unknown TextBoxInputMode");
}
return true;
}
private bool CheckIsDigit(string wert)
{
return wert.ToCharArray().All(Char.IsDigit);
}
}
public enum TextBoxInputMode
{
None,
DecimalInput,
DigitInput
}
The XAML usage looks like this:
<TextBox Text="{Binding Sum}">
<i:Interaction.Behaviors>
<Behaviors:TextBoxInputBehavior InputMode="DecimalInput"/>
</i:Interaction.Behaviors>
</TextBox>
Solution 2:
private void DecimalTextBox_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
{
bool approvedDecimalPoint = false;
if (e.Text == ".")
{
if (!((TextBox)sender).Text.Contains("."))
approvedDecimalPoint = true;
}
if (!(char.IsDigit(e.Text, e.Text.Length - 1) || approvedDecimalPoint))
e.Handled = true;
}