ios - getting error in EChart library [__NSCFString value] -

i using echart library, trying make bar chart in ipad. did make in demo project getting error :

-[__nscfstring value]: unrecognized selector sent instance 0x8bba220 2014-08-18 08:28:44.684 stat_v2_ipad[19187:70b] *** terminating app due uncaught exception 'nsinvalidargumentexception', reason: '-[__nscfstring value]: unrecognized selector sent instance 0x8bba220' 

and here error code after debugging :

/** highest value among whole chart*/ - (ecolumndatamodel *) highestvalueecolumnchart:(ecolumnchart *) ecolumnchart{     ecolumndatamodel *maxdatamodel = nil;       float maxvalue = -flt_min;      nslog(@"after flt_min : %.f",flt_min);       (ecolumndatamodel *datamodel in mergedarr)      {      nslog(@"data.value = %f",datamodel.value);      if (datamodel.value > maxvalue)      {      nslog(@"inside ifd");      maxvalue = datamodel.value;      maxdatamodel = datamodel;      }      }      nslog(@"finished max %.f",maxdatamodel.value);      return maxdatamodel; } 

problem datamodel holds nsstring instead of ecolumndatamodel . below answer prevent crash need find how string takes place?

 -(ecolumndatamodel *) highestvalueecolumnchart:(ecolumnchart *) ecolumnchart{         ecolumndatamodel *maxdatamodel = nil;           float maxvalue = -flt_min;      nslog(@"after flt_min : %.f",flt_min);       (ecolumndatamodel *datamodel in mergedarr)      { if([datamodel iskindofclass:[ecolumndatamodel class]]){      nslog(@"data.value = %f",datamodel.value);      if (datamodel.value > maxvalue)      {      nslog(@"inside ifd");      maxvalue = datamodel.value;      maxdatamodel = datamodel;      } }      }      nslog(@"finished max %.f",maxdatamodel.value);      return maxdatamodel; }