c# - Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index Emgu CV -

void framegrabber(object sender, eventargs e)         {             namepersons.clear();             namepersons.add("");              //get current frame form capture device             currentframe = grabber.queryframe().resize(320, 240, emgu.cv.cvenum.inter.cv_inter_cubic);              //convert grayscale             gray = currentframe.convert<gray, byte>();              //face detector             mcvavgcomp[][] facesdetected = gray.detecthaarcascade(           face,           1.4,           4,           emgu.cv.cvenum.haar_detection_type.do_canny_pruning,           new size(20, 20));              //action each element detected             foreach (mcvavgcomp f in facesdetected[0])             {                 t = t + 1;                 result = currentframe.copy(f.rect).convert<gray, byte>().resize(100, 100, emgu.cv.cvenum.inter.cv_inter_cubic);                 //draw face detected in 0th (gray) channel blue color                 currentframe.draw(f.rect, new bgr(color.red), 2);                   //if (trainingimages.toarray().length != 0)                 //{                     //termcriteria face recognition numbers of trained images maxiteration                     mcvtermcriteria termcrit = new mcvtermcriteria(conttrain, 0.001);                      //eigen face recognizer                     eigenobjectrecognizer recognizer = new eigenobjectrecognizer(                        trainingimages.toarray(),                        labels.toarray(),                        5000,                        ref termcrit);                     name = recognizer.recognize(result);                     groupbox1.visible = true;                     label12.text = name.trim();                     sqlcommand cmd = new sqlcommand("select * visitortb name='"+name.trim()+"'",db.connect());                     sqldatareader dr;                     dr=cmd.executereader();                     if (dr.read())                     {                         label13.text = dr[5].tostring().trim();                          label14.text = dr[10].tostring().trim();                         label16.text = dr[7].tostring().trim();                     }                      //idcrd.showidcard(name);                     //draw label each face detected , recognized                     currentframe.draw(name, ref font, new point(f.rect.x - 2, f.rect.y - 2), new bgr(color.lightgreen));                  }              namepersons[t - 1] = name;             namepersons.add("");             // }             t = 0;              //names concatenation of persons recognized             //for (int nnn = 0; nnn < facesdetected[0].length; nnn++)             //{             //    //names = names + namepersons[nnn] + ", ";             //}             ////show faces procesed , recognized             //imageboxframegrabber.image = currentframe;             ////label4.text = names;             //names = "";             ////clear list(vector) of names             //namepersons.clear();          } 

trying details of faces detected database, have been getting error "index out of range. must non-negative , less size of collection. parameter name: index" @ line

namepersons[t - 1] = name; 

you commented out if block commented out wrong closing brace. because of that, these lines appear after foreach block, when inside it:

namepersons[t - 1] = name; namepersons.add(""); 

you increment t inside foreach block, if facesdetected empty, t 0 , you'll index out of range exception.

if had stepped through code in debugger, have found problem in 2 minutes instead of hour.

another comment:

by "declare t globally" mean field of class? poor design decision. if variable used locally in method, should declared local variable of method.