C#

if (File.Exists("*.txt"))
{...}

public class ImageMemberEditor: UITypeEditor
    {
        public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
        {
            if (context != null) 
                return UITypeEditorEditStyle.DropDown;
            return base.GetEditStyle(context);
        }


        public override object EditValue(ITypeDescriptorContext context,IServiceProvider provider,object value)
        {
            if ((provider != null) && (context.Instance != null))
            {
                PropertyDescriptor descriptor = TypeDescriptor.GetProperties(context.Instance)["DataSource"];
                if (descriptor == null)
                {
                    return value;
                }
                
                object dataSource = descriptor.GetValue(context.Instance);
                if (this.DesignBindingPicker == null)
                {
                    this.designBindingPicker = new DesignBindingPicker();
                }
                DesignBinding initialSelectedItem = new DesignBinding(dataSource, (string)value);
                DesignBinding binding2 = this.designBindingPicker.Pick(context, provider, false, true, true, dataSource, string.Empty, initialSelectedItem);
                if ((dataSource != null) && (binding2 != null))
                {
                    value = binding2.DataMember;
                }
                value = lb.SelectedItem.ToString();// (dataSource as System.Windows.Forms.BindingSource).CurrencyManager.Current.ToString();
              }
            
            return value;
        }
    }