java - Unable to Start an activity when click from fragment performed -

all want on click image practice fragment open activity_lego. tried know, tried google's advice. nothing works fine.

main_activity.java

package com.example.wolfknight.tabbed;  import android.support.design.widget.tablayout; import android.support.v7.app.appcompatactivity; import android.support.v7.widget.toolbar;  import android.support.v4.app.fragment; import android.support.v4.app.fragmentmanager; import android.support.v4.app.fragmentpageradapter; import android.support.v4.view.viewpager; import android.os.bundle; import android.view.layoutinflater; import android.view.menu; import android.view.menuitem; import android.view.view; import android.view.viewgroup;   public class mainactivity extends appcompatactivity {      private sectionspageradapter msectionspageradapter;      private viewpager mviewpager;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar);         setsupportactionbar(toolbar);         msectionspageradapter = new sectionspageradapter(getsupportfragmentmanager());         mviewpager = (viewpager) findviewbyid(r.id.container);         mviewpager.setadapter(msectionspageradapter);         tablayout tablayout = (tablayout) findviewbyid(r.id.tabs);         tablayout.setupwithviewpager(mviewpager);     }     @override     public boolean oncreateoptionsmenu(menu menu) {         getmenuinflater().inflate(r.menu.menu_main, menu);         return true;     }      @override     public boolean onoptionsitemselected(menuitem item) {         int id = item.getitemid();         if (id == r.id.action_settings) {             return true;         }          return super.onoptionsitemselected(item);     }     public static class placeholderfragment extends fragment {         private static final string arg_section_number = "section_number";          public placeholderfragment() {         }         public static placeholderfragment newinstance(int sectionnumber) {             placeholderfragment fragment = new placeholderfragment();             bundle args = new bundle();             args.putint(arg_section_number, sectionnumber);             fragment.setarguments(args);             return fragment;         }          @override         public view oncreateview(layoutinflater inflater, viewgroup container,                                  bundle savedinstancestate) {             if (getarguments().getint(arg_section_number) == 1) {                 view rootview = inflater.inflate(r.layout.fragment_practice, container, false);                 return rootview;             } else if (getarguments().getint(arg_section_number) == 2) {                 view rootview = inflater.inflate(r.layout.fragment_study, container, false);                 return rootview;             }             else             {                 view rootview = inflater.inflate(r.layout.fragment_main, container, false);                 return rootview;              }         }      }     public class sectionspageradapter extends fragmentpageradapter {          public sectionspageradapter(fragmentmanager fm) {             super(fm);         }          @override         public fragment getitem(int position) {            return placeholderfragment.newinstance(position + 1);         }         @override         public int getcount() {             return 2;         }          @override         public charsequence getpagetitle(int position) {             switch (position) {                 case 0:                     return "class";                 case 1:                     return "practice";             }             return null;         }     } } 

and.... fragment>>practice.java

package layout;  import android.content.context; import android.content.intent; import android.net.uri; import android.os.bundle; import android.support.v4.app.fragment; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.button; import android.widget.imageview;  import com.example.wolfknight.tabbed.r; import com.example.wolfknight.tabbed.lego; public class practice extends fragment {      private static final string arg_param1 = "param1";     private static final string arg_param2 = "param2";      private string mparam1;     private string mparam2;      private onfragmentinteractionlistener mlistener;      public practice() {}     public static practice newinstance(string param1, string param2) {         practice fragment = new practice();         bundle args = new bundle();         args.putstring(arg_param1, param1);         args.putstring(arg_param2, param2);         fragment.setarguments(args);         return fragment;     }      @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         if (getarguments() != null) {             mparam1 = getarguments().getstring(arg_param1);             mparam2 = getarguments().getstring(arg_param2);         }     }      @override     public view oncreateview(layoutinflater inflater, viewgroup container,                              bundle savedinstancestate) {         view view = inflater.inflate(r.layout.fragment_practice, container, false);         imageview mbutton = (imageview) view.findviewbyid(r.id.image);          mbutton.setonclicklistener(new view.onclicklistener() {             public void onclick(view v) {                 intent intent = new intent(getactivity(), lego.class);                 startactivity(intent);              }         });         return view;         }     public void onbuttonpressed(uri uri) {         if (mlistener != null) {             mlistener.onfragmentinteraction(uri);         }     }      @override     public void onattach(context context) {         super.onattach(context);         if (context instanceof onfragmentinteractionlistener) {             mlistener = (onfragmentinteractionlistener) context;         } else {             throw new runtimeexception(context.tostring()                     + " must implement onfragmentinteractionlistener");         }     }      @override     public void ondetach() {         super.ondetach();         mlistener = null;     }     public interface onfragmentinteractionlistener {         void onfragmentinteraction(uri uri);     } } 

xml part works fine.. app runs nothing respond on click..

try setting button's onclicklistener in onviewcreated instead.