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Invoke member of Userdefined Type

Hello all,

I'm hoping that someone could help me with this bit of code. I am
using reflection to dynamically call a method within an HttpHandler.
When a method returns a user defined type that implements a certain
interface, I want to call that interfaces method. The problem is that
the local varaible holding the user defined type is declared an object.
The compiler will accept the invocation of the interface method on that
object. I have a feeling that I may be getting over my head a little
bit on this one. Any hekp would be greatly appreciated. Code follows:

using System;
using System.Collecti ons;
using System.Collecti ons.Specialized ;
using System.Web;
using System.Reflecti on;
using PJC.PitchBook;
using PJC.PitchBook.C lasses;
using PJC.PitchBook.D ata;
using PJC.PitchBook.W eb.UI.Ajax;

namespace PJC.PitchBook.W eb.HttpHandlers {

public class ServerMethod:IH ttpHandler {
HttpContext _context;

HttpRequest Request {
get {return _context.Reques t;}
HttpResponse Response {
get {return _context.Respon se;}
HttpContext Context {
get {return _context;}
set {_context = value;}
public void ProcessRequest( HttpContext context) {
Context = context;
NameValueCollec tion qs = Request.QuerySt ring;
AJAXHandlerRequ estStruct _values;
int i,j;
int countParams=qs. Count-1; //Will use this number later
if (countParams > -1) { //Meaning there is at least 1 (function
name) at qs[0]
_values = new AJAXHandlerRequ estStruct();
_values.Args = new ArrayList();
_values.Method= qs[0]; //Function name here
for (i=1;i<countPar ams;i++) _values.Args.Ad d(qs[qs.GetKey(i)]);
//If any parameters, pick them up here
} else {
serverResponse( 204);

MethodInfo[] myMethods =
Assembly.GetExe cutingAssembly( ).GetType("PJC. PitchBook.Web.H ttpHandlers.Ser verMethod").Get Methods();
MethodInfo theMethod;

//Get the method that matches in name and number of parameters
for (i=0;i<myMethod s.Length;i++) {
if ((myMethods[i].Name==_values. Method) &&
(myMethods[i].GetParameters( ).Length==count Params)) { //This is it!
theMethod=myMet hods[i];
Object[] args;
try {
ParameterInfo[] _params = theMethod.GetPa rameters();
int paramCount = _params.Length;
args = new Object[paramCount];

//Convert argument value to type specified by parameterInfo
for (j=0;j<paramCou nt;j++) args[j] =
Convert.ChangeT ype(_values.Arg s[j],_params[j].ParameterType) ;
Type RTYPE = theMethod.Retur nType;
object myResult = theMethod.Invok e(this,args);

// Test to see if return type implements interface
if (RTYPE.GetInter face("ToAJAX",f alse) != null) {
serverResponse( myResult.ToAJAX (true));
} else {
string[] myVals = new string[2];
myVals[0] = myResult.ToStri ng();
myVals[1] = string.Empty;
serverResponse( new AJAXHandlerResp onseStruct(myVa ls));

} catch (Exception) {
serverResponse( 204);
serverResponse( 204);
private void serverResponse (AJAXHandlerRes ponseStruct response) {
Response.Status Code = 200;
Response.Conten tEncoding = System.Text.Enc oding.UTF8;
Response.Conten tType = "text/html";
Response.Append Header("X-JSON", response.JSON);
Response.Append Header("Content-Length",
response.HTML.L ength.ToString( ));
Response.Write( response.HTML);
Response.Flush( );
Response.Close( );
private void serverResponse (int responseCode) {
Response.Status Code = responseCode;
Response.Conten tEncoding = System.Text.Enc oding.UTF8;
Response.Conten tType = "text/html";
Response.Append Header("X-JSON", "null");
Response.Append Header("Content-Length", "0");
Response.Write( string.Empty);
Response.Flush( );
Response.Close( );
public bool IsReusable {
get { return true; }

#region Server Methods
public PJC.PitchBook.W eb.UI.Ajax.PJCS ectionCollectio n
getSectionColle ction() {
return new PJC.PitchBook.W eb.UI.Ajax.PJCS ectionCollectio n();
// public AJAXHandlerResp onseStruct
getFilteredSect ionCollection(U serLevel DisplayLevel, int UserID) {
// return new
PJC.PitchBook.W eb.UI.Ajax.PJCS ectionCollectio n(DisplayLevel,
// }
// public AJAXHandlerResp onseStruct
getSearchResult sSectionCollect ion(UserLevel DisplayLevel, int UserID,
string SearchString) {
// return new
PJC.PitchBook.W eb.UI.Ajax.PJCS ectionCollectio n(DisplayLevel, UserID,
SearchString).I tems;
// }
// public AJAXHandlerResp onseStruct Expand(int id) {
// return new PJC.PitchBook.W eb.UI.Ajax.PJCS ection(id).Item s;
// }
// public AJAXHandlerResp onseStruct getCanvasCollec tion(int
CollectionID) {
// return new
PJC.PitchBook.W eb.UI.Ajax.PJCC ollection(Colle ctionID).Items;
// }
// public AJAXHandlerResp onseStruct CollectionHasVa riables(int
CollectionID) {
// PJCUser theUser = (PJCUser)Contex t.Session["User"];
// PJC.PitchBook.D ata.PJCCollecti onData _data = new
PJC.PitchBook.D ata.PJCCollecti onData(Collecti onID);
// return (_data.PageVari ableIDs.Count > 0 & theUser.UserID != 0);
// }

Sorry about the crappy formatting.


Feb 6 '06 #1
4 2002
> When a method returns a user defined type that implements a certain
interface, I want to call that interfaces method.The problem is that
the local varaible holding the user defined type is declared an object.
The compiler will accept the invocation of the interface method on that

When you call the method using reflection (MethodInfo.Inv oke in your
snippet), only the runtime-type matters. If you want to call the
interface methods, use Activator.Creat eInstance then cast the return
value to that interface.

Hope that helps,

Feb 7 '06 #2
Thanks for the quick reply. Let me get this straight. If I can
determine the return type implements an interface, I can cast the
returned instance to the interface type, then call the interfaces
methods? I am sorry, I'm not at work and I see there are some errors in
the snippet I posted. Upen further review:

//This just creates an instance of the ReturnType of the method, using
the args[] for the method in the class contructor...Th is isn't the
Type RTYPE = theMethod.Retur nType;
if (RTYPE.GetInter face("IAJAXResp onse",false) != null) {

serverResponse( ((IAJAXResponse )Activator.Crea teInstance(RTYP E,args)).ToAJAX (true));
} else {...}

//Would this work?
Type RTYPE = theMethod.Retur nType;
object myResult = theMethod.Invok e(this,args);
// Test to see if return type implements interface
if (RTYPE.GetInter face("IAJAXResp onse",false) != null) {
serverResponse( ((IAJAXResponse )myResult).ToAJ AX(true));
} else {...}


Feb 7 '06 #3
In this case, the call of CreateInstance is not necessary because you
already had the instance. So you could simply cast myResult to the
interface and call its ToAJAX method:
if (myResult is IAJAXResponse)
serverResponse( ((IAJAXResponse ) myResult).ToAJA X(true));

That requires IJAXResponse to be known at compile time (that is, you
added a reference to it the DLL containing it). Otherwise, you could
RTYPE.Invoke("T oAJAX", BindingFlags.In vokeMethod, null, myResult, new
object[] {true});


Feb 7 '06 #4
That worked perfectly and makes sense now. Thanks Thi.


Feb 7 '06 #5

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