private static void DPChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { FileRenamer fr = d as FileRenamer; if (string.IsNullOrEmpty(fr.OutputFolder) || !System.IO.Directory.Exists(fr.OutputFolder)) { fr.IsOutputFolderExists = false; } else { fr.IsOutputFolderExists = true; } fr.ProcessTags(); }