support for .NET framework 3.5

Still have bugs

Net35/HandyControlDemo_Net35/Tools/AssemblyHelper.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace HandyControlDemo.Tools
+{
+    public class AssemblyHelper
+    {
+        private static readonly string NameSpaceStr = typeof(AssemblyHelper).Assembly.GetName().Name;
+
+        public static object CreateInternalInstance(string className)
+        {
+            try
+            {
+                var type = Type.GetType($"{NameSpaceStr}.{className}");
+                return type == null ? null : Activator.CreateInstance(type);
+            }
+            catch
+            {
+                return null;
+            }
+        }
+    }
+}

Net35/HandyControlDemo_Net35/Tools/CommonHelper.cs

@@ -0,0 +1,25 @@
+using System.Linq;
+using System.Management;
+using HandyControl.Data;
+
+namespace HandyControlDemo.Tools
+{
+    public class CommonHelper
+    {
+        public static SystemVersionInfo GetSystemVersionInfo()
+        {
+            var managementClass = new ManagementClass("Win32_OperatingSystem");
+            var instances = managementClass.GetInstances();
+            foreach (var instance in instances)
+            {
+                if (instance["Version"] is string version)
+                {
+                    var nums = version.Split('.').Select(int.Parse).ToList();
+                    var info = new SystemVersionInfo(nums[0], nums[1], nums[2]);
+                    return info;
+                }
+            }
+            return default(SystemVersionInfo);
+        }
+    }
+}

Net35/HandyControlDemo_Net35/Tools/Converter/StringRepeatConverter.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Globalization;
+using System.Text;
+using System.Windows.Data;
+
+namespace HandyControlDemo.Tools.Converter
+{
+    public class StringRepeatConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            if (value is string strValue)
+            {
+                var builder = new StringBuilder();
+                int num;
+                if (parameter is string numStr)
+                {
+                    if (!int.TryParse(numStr, out num))
+                    {
+                        return strValue;
+                    }
+                }
+                else if(parameter is int intValue)
+                {
+                    num = intValue;
+                }
+                else
+                {
+                    return strValue;
+                }
+                for (var i = 0; i < num; i++)
+                {
+                    builder.Append(strValue);
+                }
+                return builder.ToString();
+            }
+            return string.Empty;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}