CODEWITHSUNDEEP
wpf
Mohd Ahmed
Mohd Ahmed

Reputation: 1482

Binding float data type with UpdateSourceTrigger set toPropertyChanged in WPF

I have a problem with Float data type while using UpdateSourceTrigger in WPF.I have a property with float data type and it is binded it to a TextBox and set its UpdateSourceTrigger of the binding to PropertyChanged,but WPF dosen't let me type '.' in the TextBox unless i change UpdateSourceTrigger to LostFocus.I think it's because of we can not type '.' in the end of float value.I don't have any idea how can i fix it because i need to type '.' and set UpdateSourceTrigger to PropertyChanged.

I have designed my textbox in such a way that it can take only 7 characters for example 1) 12.3456 2) 1234.56 e.t.c

The property is:`

 public float? Expenditure
{
    get;set;
}

And in the XAML:

<TextBox Text="{Binding Expenditure, UpdateSourceTrigger=PropertyChanged}"/>

StringFormat does not help as decimal can be put anywhere. Any help would be great.

Upvotes: 2

Views: 4224

Answers (2)

Sergey Alekseev
Sergey Alekseev

Reputation: 63

I wrote a value converter, that solves your problem:

Usage:

<Window x:Class="BindingExample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:BindingExample"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <local:DoubleToStringConverter x:Key="DoubleToStringConverter" DigitsCount="5"/>
    </Window.Resources>
    <StackPanel>
        <TextBox Text="{Binding FloatProperty, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource DoubleToStringConverter}}" Margin="5"/>
    </StackPanel>
</Window>

Converter:

[ValueConversion(typeof(double), typeof(string))]
public class DoubleToStringConverter : IValueConverter
{
    #region IValueConverter Members

    public DoubleToStringConverter()
    {
        // Default value for DigitsCount
        DigitsCount = 7;
    }

    // Convert from double to string
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return null;

        double doubleValue = System.Convert.ToDouble(value);

        // Calculate digits count
        int digitsBeforePoint = System.Convert.ToInt32(Math.Ceiling(Math.Log10(doubleValue)));
        int digitsAfterPoint = DigitsCount - digitsBeforePoint;

        // TODO: You have to handle cases where digitsAfterPoint < 0

        // Create formatString that is used to present doubleValue in desired format     
        string formatString = String.Format("{{0:F{0}}}", digitsAfterPoint);

        return String.Format(formatString, doubleValue);
    }

    // Convert from string to double
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return null;

        double? result = null;

        try
        {
            result = System.Convert.ToDouble(value);
        }
        catch
        {
        }

        return result.HasValue ? (object)result.Value : DependencyProperty.UnsetValue;
    }

    public int DigitsCount { get; set; }

    #endregion
}

Upvotes: 2

Sergey Alekseev
Sergey Alekseev

Reputation: 63

Just change StringFormat property of the binding to display two decimal places of the property:

<TextBox Text="{Binding Expenditure, UpdateSourceTrigger=PropertyChanged, StringFormat='{}{0:F2}'}"/>

Also you can write a custom FloatToStringConverter (here is an example). Your own float-to-string and string-to-float conversion methods will allow you to handle empty text field of TextBox and convert it to null.

Upvotes: 2

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