Android: getview principle in listview [Android] principle of getview in listview + how to place multiple items in listview

In fact, the reuse technology here is very common in the list, tableview in the iPhone also has related technologies, cell Reuse

Working principle:

1. For each item in the list, listview requires the adapter to "give me a view" (getview ).
2. A New View is returned and displayed.

What if we want to display hundreds of millions of projects? Create a new view for each project? No! This is impossible!

In fact, Android caches the view for you.

There is a recycler component in Android that works as follows:

1. If you have 1 billion items, only visible items are in memory, and others are in recycler.
2. Listview first requests a type1 view (getview) and then requests other visible projects. Convertview is null in getview.
3. When Item1 is out of the screen and a new project is down from the screen, listview requests a type1 view. Convertview is not a null value. Its value is item1. You only need to set new data and return convertview. You do not need to create a new view.

See the following example.CodeIn getview, system. Out is used for output.

 Public   Class Multipleitemslist Extends Listactivity {  Private  Mycustomadapter madapter; @ override  Public   Void  Oncreate (bundle savedinstancestate ){  Super  . Oncreate (savedinstancestate); madapter = New  Mycustomadapter ();  For ( Int I = 0; I <50; I ++ ) {Madapter. additem ( "Item" + I);} setlistadapter (madapter );}  Private   Class Mycustomadapter Extends  Baseadapter {  Private Arraylist mdata = New  Arraylist ();  Private  Layoutinflater minflater;  Public  Mycustomadapter () {minflater =(Layoutinflater) getsystemservice (context. layout_inflater_service );}  Public   Void Additem ( Final  String item) {mdata. Add (item); policydatasetchanged () ;}@ override  Public   Int  Getcount (){  Return  Mdata. Size () ;}@ override  Public String getitem ( Int Position ){  Return  Mdata. Get (position) ;}@ override  Public   Long Getitemid ( Int  Position ){  Return  Position ;}@ override  Public View getview ( Int  Position, view convertview, viewgroup parent) {system. Out. println ( "Getview" + Position + "" +Convertview); viewholder holder = Null  ;  If (Convertview = Null  ) {Convertview = Minflater. Inflate (R. layout. Item1, Null  ); Holder = New  Viewholder (); Holder. textview = (Textview) convertview. findviewbyid (R. Id. Text); convertview. settag (holder );} Else  {Holder = (Viewholder) convertview. gettag ();} holder. textview. settext (mdata. Get (position ));  Return  Convertview ;}}  Public   Static   Class  Viewholder {  Public  Textview ;}} 

Several items will not call functions that instantiate convertview after initialization. If (convertview = NULL) will not be executed, so data and corresponding listening should be set outside of it.

 

Note:

Convertview is the most out-of-the-box layout in R. layout. Item1.

Reference:

[Android] principle of getview in listview + how to place multiple items in listview