Reflection is all about the ability to examine the capabilities of classes at runtime. Most of the objects involved in reflection can be found in System.Reflection

Reflection enables you to take an object and examine its methods, properties, constructors, fields, events and other members.

Reflection is centered around System.Type, this object describes a type, and in most cases this type will represent a class inside an assembly, represented by System.Reflection.Assembly.

System.Type provides methods like GetMethods and GetProperties to return member information. Looking deeper into the results (for example, System.Reflection.MethodInfo) can tell you the parameters and even let you call into the member through Invoke.

The following image represents the ILDASM tool (Ships with the .NET Framework), it mainly is a reflector of Assemblies.  It allows you to load any valid .NET Assembly and dive into its properties, methods and other members to discover its characteristics and its run time type information.

Better yet, if you download the Lutz Roeders .NET Reflector from http://www.aisto.com/roeder/dotnet

You will be able to do everything ILDASM does and much more.  See the image below to examine the capabilities of this reflector tool, where the system is hooked up to the MSDN and a XML documentation viewer.

Finally, some code to allow you to build your own Reflector in Delphi for .NET 

This code is simple enough to allow you to load a .NET Assembly, in this case we load mscorlib.dll but you can change that to any .NET Assembly you wish to examine.

 Concentrate on the following tips:

• How to access Environment Variables ` Environment.GetEnvironmentVariable('systemroot');
• How to load Assemblies ` Assembly.LoadFrom();
• How to type cast arrays ` System.Array();
• How to dig into for loops to getTypes, GetProperties, GetMethods, etc (This will change once ForEach equivalent makes it into the language for the .NET release of Delphi.

 The complete source code for this sample can be downloaded from

http://codecentral.borland.com/codecentral/ccWeb.exe/listing?id=19426

procedure TReflectionForm.btnLoad_Click(Sender: TObject; E: EventArgs);
var
  SysRoot: String;
  Assm: Assembly;
  T: array of System.Type;
  i, iprop: integer;
  PropertyCount, MethodCount, FieldCount, EventCount: integer;
  TN, TNProp, TNMethod, TNEvent, TNField: TreeNode;
begin
  SysRoot:= Environment.GetEnvironmentVariable('systemroot');
  try
    Assm:= Assembly.LoadFrom(SysRoot + 'Microsoft.NETFrameworkv1.1.4322mscorlib.dll');
    SetLength(t, System.Array(Assm.GetTypes()).Length);
    t:= Assm.GetTypes();
    for i:= 0 to System.Array(Assm.GetTypes()).Length - 1 do
    begin
      TN:= TV.Nodes.Add(t[i].Name);

      PropertyCount := PropertyCount + System.Array(t[i].GetProperties()).GetUpperBound(0) + 1;
      TNProp:= TN.Nodes.Add('Properties');
      for iprop:= 0 to System.Array(t[i].GetProperties()).Length - 1 do
        TNProp.Nodes.Add(System.Array(t[i].GetProperties()).GetValue(iprop).tostring());

      MethodCount:= MethodCount + System.Array(t[i].GetMethods()).GetUpperBound(0) + 1;
      TNMethod:= TN.Nodes.Add('Methods');
      for iprop:= 0 to System.Array(t[i].GetMethods()).Length - 1 do
        TNMethod.Nodes.Add(System.Array(t[i].GetMethods()).GetValue(iprop).tostring());

      FieldCount:= FieldCount + System.Array(t[i].GetFields()).GetUpperBound(0) + 1;
      TNField:= TN.Nodes.Add('Fields');
      for iprop:= 0 to System.Array(t[i].GetFields()).Length - 1 do
        TNField.Nodes.Add(System.Array(t[i].GetFields()).GetValue(iprop).tostring());

      EventCount:= EventCount + System.Array(t[i].GetEvents()).GetUpperBound(0) + 1;
      TNEvent:= TN.Nodes.Add('Events');
      for iprop:= 0 to System.Array(t[i].GetEvents()).Length - 1 do
        TNEvent.Nodes.Add(System.Array(t[i].GetEvents()).GetValue(iprop).tostring());
  end;
  except
    MessageBox.Show('Kaboom!! Problems loading the assembly'); //implement your own exception handling here.
  end;
  Self.Text:= 'Properties=' + IntToStr(PropertyCount) + '  Methods=' + IntToStr(MethodCount) + ' Fields=' 

    + IntToStr(FieldCount) + ' Events=' + IntToStr(EventCount);
  stBar.Text :='Done';
end;

If you are not running the latest .NET Framework 1.1 Beta, please change the code to load from the "v1.0.3705" instead of "v1.1.4322"

Add some more to this code and play around with Reflection and see how easy it is to dig in and reflect information back from any .NET Assembly.  In future, more advanced articles, I will show how to invoke methods in .NET Assemblies using Reflection, which is WAY COOL!

Happy New Year and write to you later J

About Falafel Software Inc:

Falafel Software is all about making the most of software development technology in order to complete the project on time and on budget with best possible user experience. Falafel Software offers a comprehensive suite of software development solutions ranging from strategy to design to implementation that businesses need in order to realize high returns on their investment.

Copyright ) 2003 Alain Tadros, Falafel Software Inc.
ALL RIGHTS RESERVED. NO PART OF THIS DOCUMENT CAN BE COPIED IN ANY FORM WITHOUT THE EXPRESS, WRITTEN CONSENT OF THE AUTHOR.