>I have a WPF application with MVVM and need to show a label over a textbox that indicates the remaining number of characters allowed to be in the textbox. I can't seem to wrap my head around the best way to do this.
>
>The user is able to type up to 183 characters in the text box. I would like to show a label above it that indicates (Max Characters: 183). But as they type, I want to show (Remaining Characters: 182). Once they reach 0 it should be 0 but then show in red.
>
>The text box is bound to a property in the View Model which I could get a count on easy enough, however how would I raise the event indicating the text property has changed? WPF does not access the property setters directly.

I'm sure you've implemented this by now but here's one solution:

<Window x:Class="WpfApplication4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfApplication4"
        Title="MainWindow" Height="350" Width="525"
        >
    <Window.Resources>
         <local:ViewModel x:Key="VM"/>
    </Window.Resources>
    <StackPanel DataContext="{StaticResource VM}">
         <TextBox x:Name="txtBox" Text="{Binding Path=TheText, UpdateSourceTrigger=PropertyChanged}"></TextBox>
        <Label Content="{Binding Path=LabelText}"></Label>
    </StackPanel>
</Window>

where ViewModel (I bodged the MaxLength) is:

    public class ViewModel : DependencyObject, INotifyPropertyChanged
    {
        int MaxLength = 183;

        public string LabelText
        {
            get
            {
                if ( TheText==null || TheText.Length == 0)
                    return string.Format("Max Characters: {0}", MaxLength);
                else
                    return string.Format("Remaining Characters: {0}", MaxLength - TheText.Length);
            }
        }


        private string theText;
        public string TheText
        {
            get { return theText; }
            set
            {
                theText = value;
                OnPropertyChanged("TheText");
                OnPropertyChanged("LabelText");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        void OnPropertyChanged(string s)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(s));
        }
    }

You could, of course bind the label directly to the TextBox.Text.Length in XAML and use a ValueConverter but I assumed you wanted a clean MVVM approach....