How to save an expandable listview in android? -


i have expandable listview can add too. how can save every item added. have tried using sharedpreferences gson json, doesn't seem work. here expandable listview adapter: 

public class expandlistadapter extends baseexpandablelistadapter {     private context context;     private arraylist<group> groups;      public expandlistadapter(context context, arraylist<group> groups) {         this.context = context;         this.groups = groups;     }      @override     public object getchild(int groupposition, int childposition) {         arraylist<child> chlist = groups.get(groupposition).getitems();         return chlist.get(childposition);     }      @override     public long getchildid(int groupposition, int childposition) {         return childposition;     }      @override     public view getchildview(int groupposition, int childposition,                          boolean islastchild, view convertview, viewgroup parent) {          child child = (child) getchild(groupposition,                    childposition);         if (convertview == null) {              layoutinflater infalinflater = (layoutinflater) context                      .getsystemservice(context.layout_inflater_service);              convertview = infalinflater.inflate(r.layout.child_row, null);         }         textview tv = (textview) convertview.findviewbyid(r.id.country_name);         tv.settext(child.getname().tostring());          return convertview;      }      @override     public int getchildrencount(int groupposition) {         arraylist<child> chlist = groups.get(groupposition)                 .getitems();          return chlist.size();     }      @override     public object getgroup(int groupposition) {         return groups.get(groupposition);     }      @override     public int getgroupcount() {         return groups.size();     }      @override     public long getgroupid(int groupposition) {         return groupposition;     }      @override     public view getgroupview(int groupposition, boolean isexpanded,                              view convertview, viewgroup parent) {         group group = (group) getgroup(groupposition);         if (convertview == null) {             layoutinflater inf = (layoutinflater) context                     .getsystemservice(context.layout_inflater_service);             convertview = inf.inflate(r.layout.group_header, null);         }         textview tv = (textview) convertview.findviewbyid(r.id.group_name);         tv.settext(group.getname());         return convertview;     }      @override     public boolean hasstableids() {         return true;     }      @override     public boolean ischildselectable(int groupposition, int childposition) {         return true;     }

here class uses expandable listview, can add groups alertdialog , adds child name of "yo", testing reasons: 

public class classesscreen extends activity implements adapterview.onitemselectedlistener { private expandlistadapter expadapter; private expandablelistview expandlist; private button newheaderbut; static arraylist<group> group_list; arraylist<child> child_list; string m_text;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_classes);      group_list = new arraylist<group>();      expandlist = (expandablelistview) findviewbyid(r.id.classeslistview);     expadapter = new expandlistadapter(this, group_list);     expandlist.setadapter(expadapter);       newheaderbut = (button) findviewbyid(r.id.newclassbut);      newheaderbut.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {              alertdialog.builder builder = new alertdialog.builder(classesscreen.this);             builder.settitle("add new class:");              final edittext input = new edittext(classesscreen.this);              builder.setview(input);              builder.setpositivebutton("ok", new dialoginterface.onclicklistener() {                 @override                 public void onclick(dialoginterface dialog, int which) {                      m_text = input.gettext().tostring();                      group gru1 = new group();                     gru1.setname(m_text);                      child_list = new arraylist<child>();                      child ch1 = new child();                     ch1.setname("yo");                      child_list.add(ch1);                      gru1.setitems(child_list);                      group_list.add(gru1);                     expadapter.notifydatasetchanged();                 }             });              builder.setnegativebutton("cancel", new dialoginterface.onclicklistener() {                 @override                 public void onclick(dialoginterface dialog, int which) {                     dialog.cancel();                 }             });             builder.show();        });     }      public void onitemselected(adapterview<?> parent, view view, int position, long id){}      public void onnothingselected(adapterview<?> arg0) {} }

i have 2 object class called group , child. can show if need them. in advance!

save latest arraylist file 

    private void savedatatofile() {      fileoutputstream fileoutputstream = null;     try {         fileoutputstream = getcontext().openfileoutput("filename", context.mode_private);     } catch (filenotfoundexception e) {         e.printstacktrace();     } catch (nullpointerexception e) {      }     objectoutputstream objectoutputstream = null;     try {         objectoutputstream = new objectoutputstream(fileoutputstream);     } catch (ioexception e) {         e.printstacktrace();     } catch (nullpointerexception e) {      }     try {         if (objectoutputstream != null) {             objectoutputstream.writeobject(yourarraylist); //which data u want save         }     } catch (ioexception e) {         e.printstacktrace();     }     try {         if (objectoutputstream != null) {             objectoutputstream.close();         }     } catch (ioexception e) {         e.printstacktrace();     } }

retrieve data file

    private void getdatafromfile() {      fileinputstream fileinputstream = null;     try {         fileinputstream = getcontext().openfileinput("filename");     } catch (filenotfoundexception e) {         e.printstacktrace();         return;     }     objectinputstream objectinputstream = null;     try {         objectinputstream = new objectinputstream(fileinputstream);     } catch (ioexception |nullpointerexception e) {         e.printstacktrace();     }     try {         yourarraylist = (arraylist<yourclassname>) objectinputstream.readobject();     } catch (ioexception e) {         e.printstacktrace();     } catch (classnotfoundexception e) {         e.printstacktrace();     }     try {         objectinputstream.close();     } catch (ioexception e) {         e.printstacktrace();     }  }

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