Viewholder Official API Demos

/* Copyright (C) The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License") ; * You are not a use this file except in compliance with the License. * Obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * unless required by appli Cable law or agreed into writing, software * Distributed under the License is distributed on a "as is" BASIS, * without Warranties or CONDITIONS of any KIND, either express OR implied. * See the License for the specific language governing permissions and * limitations under the License. */package Com.example.android.apis.view;import Android.app.listactivity;import Android.content.Context;import Android.os.bundle;import Android.view.layoutinflater;import Android.view.view;import Android.view.ViewGroup; Import Android.widget.baseadapter;import Android.widget.textview;import Android.widget.imageview;import Android.graphics.bitmapfactory;import Android.graphics.bitmap;import Com.example.android.apis.r;/** * Demonstrates how to write a efficient list adapter. The adapter used in this example binds * to an ImageView and to a TextView for each row in the list. * To work efficiently The adapter implemented here uses a techniques: *-It reuses the Convertview passed to GetView (  ) to avoid inflating View when it's not necessary *-it uses the Viewholder pattern to avoid calling Findviewbyid () when It is not necessary * * The Viewholder pattern consists in storing a data structure in the tag of the view returned by * GetView (). This data structures contains references to the views we want to bind data to, thus * avoiding calls to Findviewbyid () Eve Ry Time GetView () is invoked.  */public class List14 extends Listactivity {private static class Efficientadapter extends Baseadapter {private        Layoutinflater Minflater;        Private Bitmap MIcon1;        Private Bitmap MIcon2; Public Efficientadapter (Context context) {//Cache the LayoutiNflate to avoid asking for a new one each time.            Minflater = Layoutinflater.from (context);            Icons bound to the rows.            MIcon1 = Bitmapfactory.decoderesource (Context.getresources (), r.drawable.icon48x48_1);        MIcon2 = Bitmapfactory.decoderesource (Context.getresources (), r.drawable.icon48x48_2);         /** * The number of the items in the list are determined by the number of speeches * in our array. * * @see Android.widget.listadapter#getcount () */public int getcount () {return D        Ata.length; }/** * Since The data comes from a array, just returning the index is * sufficent-get at the D Ata.         If we were using a more complex data * structure, we would return whatever object represents one row in the         * list.            * * @see android.widget.listadapter#getitem (int) */public Object getItem (int position) { RetuRN position;         }/** * Use the array index as a unique ID.            * * @see android.widget.listadapter#getitemid (int) */public long getitemid (int position) {        return position;         }/** * Make a view to hold each row.         * * @see android.widget.listadapter#getview (int, Android.view.View, * android.view.ViewGroup) */Public View getView (int position, View Convertview, ViewGroup parent) {//A Viewholder keeps Refere            NCEs to children views to avoid unneccessary calls//to Findviewbyid () on each row.            Viewholder Holder; When convertview are not NULL, we can reuse it directly, there are no need//to reinflate it.            We only inflate a new View when the Convertview supplied//by ListView is null. if (Convertview = = null) {Convertview = minflater.inflate (R.layout.list_item_icon_text, NULL);               Creates a viewholder and store references to the other children views//We want to bind Da                Ta to.                Holder = new Viewholder ();                Holder.text = (TextView) Convertview.findviewbyid (R.id.text);                Holder.icon = (ImageView) Convertview.findviewbyid (R.id.icon);            Convertview.settag (holder);                 } else {//Get the Viewholder back-to-get fast access to the TextView//and the ImageView.            Holder = (viewholder) convertview.gettag ();            }//Bind the data efficiently with the holder.            Holder.text.setText (Data[position]);            Holder.icon.setImageBitmap ((position & 1) = = 1? micon1:micon2);        return convertview;            } static class Viewholder {TextView text;        ImageView icon; }} @Override public void OnCreate (Bundle savedinstancestate) {super.oncreate (SavedinstaNcestate);    Setlistadapter (New Efficientadapter (this)); } private static Final string[] DATA = cheeses.scheesestrings;}

　　

Viewholder Official API Demos