电量显示Binding Converter MVVM

用一个ProcessBar显示电量，低于20%时候,ForeGround为红色，否则为绿色，

页面使用了MVVM绑定到了ViewModel, ProcessBar XAML为

<ProgressBar  Maximum="100" Value="{Binding RemainPercent}"
 Foreground="{Binding RemainPercent, Converter={StaticResource ForgroundConverter}}" ></ProgressBar>

其中  ForgroundConverter为资源的key

xmlns:converter ="clr-namespace:XXX.XXX"

<UserControl.Resources>
        <converter:PercentForgroundConverter x:Key="ForgroundConverter"/>
    </UserControl.Resources>

PercentForgroundConverter 为实现了IValueConverter的类，方法如下，

Brushes的命名空间为System.Windows.Media。

public class PercentForgroundConverter:IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            double percent = (double)value;
            if (percent<=20)
            {
                return Brushes.Red;
            }
            return Brushes.Green;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }