Change foreground color of textbox when text changes and meets certain criterion

Question

I require to set text color when text changes inside textbox and meets certain criterion. I can implement this from code behind with textbox_textchanged event and set brushes.color to desired color.

But I am not being able to implement this with xaml wpf approach. I am new to wpf, I'm not sure how can I set text color depending upon certain criterion when text changes in textbox.

For example: For a given textbox, when text changes, it needs to determine if input text is a number then change foreground color to green else red.

Looking forward for the help. Thank you in advance.

Colin Colin · Accepted Answer · 2013-06-07T15:20:08

I am not sure whether a binding converter is allowed in your situation. But here is a solution which only needs a binding converter in your code behind.

Here is the code in xaml

    <Grid.Resources>
        <local:ValueConverter x:Key="ValueConverter"></local:ValueConverter>
    </Grid.Resources>
    <TextBox Text="{Binding Text,UpdateSourceTrigger=PropertyChanged}">
        <TextBox.Style>
            <Style>
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=Text,Converter={StaticResource ValueConverter}}" Value="True">
                        <Setter Property="TextBox.Foreground" Value="Red"></Setter>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </TextBox.Style>
    </TextBox>

Here is the view model and the value converter

public class ViewModel : INotifyPropertyChanged
{
    private string _text;

    public string Text
    {
        get
        {
            return this._text;
        }
        set
        {
            this._text = value;
            if (null != PropertyChanged)
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs("Text"));
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

public class ValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (null != value)
        {
            if (value.ToString() == "1")
                return true;
        }
        return false;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return null;
    }
}

So the solution uses the data trigger to fulfill the goal. The only reason for using binding converter here is that you need a place to determine what kind of value should change the foreground of the TextBox. Here the foreground of TextBox will be red when the value of the TextBox is "1".

Change foreground color of textbox when text changes and meets certain criterion

4 Answers