android - What is the working of setTag and getTag in ViewHolder pattern? -

i have simple code snippet implementing custom listview.

my code follows:

weatheradapter.java :

public class weatheradapter extends arrayadapter<weather>{      context mcontext;      int mlayoutresourceid;        weather mdata[] = null;    view row;      public weatheradapter(context context, int layoutresourceid, weather[] data) {         super(context, layoutresourceid, data);         mlayoutresourceid = layoutresourceid;        mcontext = context;         mdata = data;     }      @override     public view getview(int position, view convertview, viewgroup parent) {       row = convertview;         weatherholder holder = null;          if(row == null)         {             layoutinflater inflater = ( (activity) mcontext).getlayoutinflater();             row = inflater.inflate(mlayoutresourceid, parent, false);              holder = new weatherholder(row);               row.settag(holder);          }         else         {             holder = (weatherholder)row.gettag();         }          weather w = mdata[position];         holder.txttitle.settext(w.mtitle);         holder.imgicon.setimageresource(w.micon);          return row;     } 

weatherholder.java:

class weatherholder     {         imageview imgicon;         textview txttitle;       public weatherholder(view v){            imgicon = (imageview)row.findviewbyid(r.id.imgicon);           txttitle = (textview)row.findviewbyid(r.id.txttitle);      }     } } 

i have seen many answers on , other sites , understood recycling mechanism of listview.

i understood viewholder, can hold child views in adapter , not have call findviewbyid() many times. so, optimization.

but have confusion in settag(holder) , gettag() methods. from question, came know making key-value pair on multiple objects, can access them easily. but, not understand why required here...because, not have multiple holder objects...only have change holder's variables each time. can code here without using settag , gettag?

can explain better settag , gettag "here"?

tag mechanism make views remember something, object integer string or like.

so when listview going create first time convertview null. create new convertview , put of references of objects of row in viewholder. save viewholder memory of convertview(settag). android takes convertview , puts in pool recycle , passes again you. pool may not have enough convertviews again passes new convertview thats null. again story repeated till pool of android filled up. after android takes convertview pool , passes you. find not null ask object references gave first time? (gettag) , whatever like.

more elaboration on below line

but pool may not have enough convertviews again passes new convertview thats null

android pool empty when listview going create. first item of listview sends convertview must displayed. after android saves in pool, pool contains 1 convertview. second item of listview going create android can not use pool because has 1 element , element first item , being shown right has pass convertview. process repeates until android found convertview in pool thats not being displayed , passes you.

android inflates each row till screen filled after when scroll list uses holder.