WPF Custom TextBox with Decimal Formatting

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I am new to WPF. I have a requirement that I need to develop a custom textbox control which should support the functionality like:

Should accept only decimal values.

Should round off to 3 decimal places when assigned a value through code or by the user.

Should show the full value(without formatting) on focus.

Eg:

If 2.21457 is assigned to textbox(by code or by user), it should display 2.215. When user clicks in it to edit it, it must show the full value 2.21457. After the user edits the value to 5.42235 and tabs out, it should again round off to 5.422.

Tried it without success. So need some help on it. Thanks in advance for the help.

Thanks

[Edit - Kenneth Haugland]
Hey, Sorry for the late reply. I tried creating a custom control. It does contain some drawbacks but working on it.

C#

class TextBoxEx:TextBox
{
    public string ActualText
    {
        get { return (string)GetValue(ActualTextProperty); }
        set { SetValue(ActualTextProperty, value); }
    }

    // Using a DependencyProperty as the backing store for ActualText.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ActualTextProperty =
        DependencyProperty.Register("ActualText", typeof(string), typeof(TextBoxEx), new PropertyMetadata(string.Empty, OnActualTextChanged));

    private static void OnActualTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        TextBox tx = d as TextBox;
        tx.Text = (string)e.NewValue;
        string str = tx.Text;            
        double dbl = Convert.ToDouble(str);
        str = string.Format("{0:0.###}", dbl);
        tx.Text = str;
    }

    public TextBoxEx()
    {
        this.GotFocus += TextBoxEx_GotFocus;
        this.LostFocus += TextBoxEx_LostFocus;
        this.PreviewTextInput += TextBoxEx_PreviewTextInput;
    }

    void TextBoxEx_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
    {
        decimal d;
        if(!decimal.TryParse(e.Text,out d))
        {
            e.Handled = true;
        }
    }        

    void TextBoxEx_LostFocus(object sender, System.Windows.RoutedEventArgs e)
    {
        ConvertText();
    }

    void TextBoxEx_GotFocus(object sender, System.Windows.RoutedEventArgs e)
    {
        this.Text = ActualText;
    }

    private void ConvertText()
    {
        string str = this.Text;
        ActualText = str;
        double dbl = Convert.ToDouble(str);
        str = string.Format("{0:0.###}", dbl);
        this.Text = str;
    }
}

[/Edit]

Posted 20-Feb-15 20:37pm

hemanth kr

Updated 3-Mar-15 2:17am

Kenneth Haugland

v2

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Comments

Sergey Alexandrovich Kryukov 21-Feb-15 2:44am

What have you tried so far?
—SA

3 solutions

Solution 1

You can handle this event: https://msdn.microsoft.com/en-us/library/system.windows.uielement.previewtextinput%28v=vs.110%29.aspx[^].

The event is cancellable so you can cancel input if the user is trying to input something wrong. Please see this review: https://msdn.microsoft.com/en-us/library/ms754010%28v=vs.110%29.aspx[^].

Now, you should allow decimal point and digits. To find out if some character is digit, you can use https://msdn.microsoft.com/en-us/library/7f0ddtxh%28v=vs.110%29.aspx[^].

To find out if a character is '.', you should not hard-code it. Instead, it's better to compare a character with the decimal separator for current culture: https://msdn.microsoft.com/en-us/library/system.globalization.numberformatinfo.numberdecimalseparator%28v=vs.110%29.aspx[^].

You can always use neutral culture if you want unified format on different systems.

Also, you need to allow character with code point 8, backspace. By some reasons (historical?) this key press is treated as a character, not virtual key code.

—SA

Posted 20-Feb-15 20:53pm

Sergey Alexandrovich Kryukov

Updated 20-Feb-15 20:54pm

v2

Solution 3

Id think I would use String Fomat to show values:

XML

<textbox name="MyTextBox" text="{Binding Path=MyValue, Mode=TwoWay, StringFormat={}{0:F2}}" />

Posted 3-Mar-15 2:19am

Kenneth Haugland

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hemanth kr · Accepted Answer · 2015-03-03T02:13:00

Hey, Sorry for the late reply. I tried creating a custom control. It does contain some drawbacks but working on it.

class TextBoxEx:TextBox
{
public string ActualText
{
get { return (string)GetValue(ActualTextProperty); }
set { SetValue(ActualTextProperty, value); }
}

// Using a DependencyProperty as the backing store for ActualText. This enables animation, styling, binding, etc...
public static readonly DependencyProperty ActualTextProperty =
DependencyProperty.Register("ActualText", typeof(string), typeof(TextBoxEx), new PropertyMetadata(string.Empty, OnActualTextChanged));

private static void OnActualTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TextBox tx = d as TextBox;
tx.Text = (string)e.NewValue;
string str = tx.Text;
double dbl = Convert.ToDouble(str);
str = string.Format("{0:0.###}", dbl);
tx.Text = str;
}

public TextBoxEx()
{
this.GotFocus += TextBoxEx_GotFocus;
this.LostFocus += TextBoxEx_LostFocus;
this.PreviewTextInput += TextBoxEx_PreviewTextInput;
}

void TextBoxEx_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
{
decimal d;
if(!decimal.TryParse(e.Text,out d))
{
e.Handled = true;
}
}

void TextBoxEx_LostFocus(object sender, System.Windows.RoutedEventArgs e)
{
ConvertText();
}

void TextBoxEx_GotFocus(object sender, System.Windows.RoutedEventArgs e)
{
this.Text = ActualText;
}

private void ConvertText()
{
string str = this.Text;
ActualText = str;
double dbl = Convert.ToDouble(str);
str = string.Format("{0:0.###}", dbl);
this.Text = str;
}
}