WPF

<TextBox PreviewTextInput="PreviewTextInputHandler"
         DataObject.Pasting="PastingHandler" />

<Style x:Key="percentageStyle" 
        TargetType="{x:Type TextBox}"
        BasedOn="{StaticResource textBoxStyle}">

<pre>
<Setter Property="Text" Value="{Binding SelectedStatesCountiesCities.TaxRate, StringFormat={}{0:N2}%}" />
<Style.Triggers>
    <Trigger Property="IsKeyboardFocused" Value="True">
        <Setter Property="Text" Value="{Binding SelectedStatesCountiesCities.TaxRate}" />
    </Trigger>
</Style.Triggers>

<TextBox Grid.Row="1"
            Grid.Column="2"
            Text="{Binding SelectedStatesCountiesCities.TaxRate, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
            Style="{StaticResource percentageStyle}"
            HorizontalAlignment="Left"
            IsEnabled="True"
            Width="100"/>

<ComboBox Grid.Row="0"
            Grid.Column="1"
            ItemsSource="{Binding JobVendors, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
            SelectedItem="{Binding SelectedVendor, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
            Style="{StaticResource localComboStyle}"/>

private CompanyHeaderEntity _SelectedVendor;
public CompanyHeaderEntity SelectedVendor
{
    get { return _SelectedVendor; }
    set
    {
        var currentVendor = _SelectedVendor;

        if (_SelectedVendor != value)
        {
            bool okToChange = true;

            if (!_isLoading &&
                PurchaseOrderHeader.PurchaseOrderItems != null &&
                PurchaseOrderHeader.PurchaseOrderItems.Count > 0)
            {
                var message = "Changing vendors will remove all selected items. Continue?";
                okToChange = MessageBox.Show(message, "Change Vendor", MessageBoxButton.YesNo, MessageBoxImage.Question) == MessageBoxResult.Yes;

                if (okToChange)
                {
                    PurchaseOrderHeader.PurchaseOrderItems.Clear();
                }
            }

            if (okToChange)
            {
                _SelectedVendor = value;
                RaisePropertyChanged("SelectedVendor");

                VendorSelected();
            }
            else
            {
                if (currentVendor != null)
                {
                    _SelectedVendor = currentVendor;
                }
            }
        }
    }
}

public class MyClass : INotifyPropertyChanged
{
    private string currentFile;
    private int    fileCount  ;
    public string CurrentFile 
    { 
        get {return this.currentFile;} 
        set {if(value!=this.currentFile){this.currentFile=value;this.NtfyPropChange();}}
    }
    public int FileCount
    { 
        get {return this.fileCount;} 
        set {if (value != this.fileCount){this.fileCount=value;this.NtfyPropChange();}}
    }

    public MyClass()
    {
        this.CurrentFile = string.Empty;
        this.FileCount   = 0;
    }

    public void DoSomethingWithFiles()
    {
        string[] files = Directory,.GetFiles(@"c:\mypath", *.*);
        foreach(string file in files)
        {
            this.CurrentFile = file;
            this.FileCount += 1;
        }
    }
}

<TextBlock Text="{Binding x:Name="textblockCurrentFile" Path=myObject.CurrentFile}"/>
<TextBlock Text="{Binding x:Name="textblockFileCount" Path=myObject.FileCount}"/>

private void Tfs_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
    Dispatcher.BeginInvoke(new Action(() => 
    {
        this.textblockCurrentFile.Text = this.myObject.CurrentFile;
        this.textblockFileCount.Text = this.myObject.FileCount.ToString();
    }));
}