Android之ViewHolder用法
2015-01-23 10:38
435 查看
先声明一下ViewHolder在Android自定义的适配器中使用。目的:优化资源,节省空间,避免重复绘制view而引起的不必要的内存损耗。
我自己以前的写法:
看一下官方的API:
我自己以前的写法:
public class PlateAdapter extends BaseAdapter { private List<Plate> list; private Context context; public PlateAdapter(List<Plate> list, Context context) { super(); this.list = list; this.context = context; } @Override public int getCount() { // TODO Auto-generated method stub return list.size(); } @Override public Object getItem(int arg0) { // TODO Auto-generated method stub return list.get(arg0); } @Override public long getItemId(int arg0) { // TODO Auto-generated method stub return arg0; } @Override public View getView(int arg0, View arg1, ViewGroup arg2) { // TODO Auto-generated method stub if(arg1 == null){ arg1 = LayoutInflater.from(context).inflate(R.layout.select_car_type_list_item, null); } TextView text = (TextView)arg1.findViewById(R.id.text); text.setText(list.get(arg0).getPlateType()); return arg1; } }学习过ViewHolder之后的写法:
@SuppressWarnings("unused") public class NoticeAdapter extends BaseAdapter{ private Context _context; private List<ExamNotice> _list; public NoticeAdapter(Context context, List<ExamNotice> list) { super(); this._context = context; this._list = list; } public void set_list(List<ExamNotice> _list) { this._list = _list; } @Override public int getCount() { return _list.size(); } @Override public Object getItem(int arg0) { return _list.get(arg0); } @Override public long getItemId(int arg0) { return arg0; } @Override public View getView(int position, View convertView, ViewGroup parent) { Holder holder; if(null==convertView){ convertView=View.inflate(_context, R.layout.notice_item, null); holder=new Holder(); holder.studyPlanName=(TextView)convertView.findViewById(R.id.xxjh_item_name); holder.studyPlanDate=(TextView)convertView.findViewById(R.id.xxjh_item_date); convertView.setTag(holder); }else{ holder=(Holder)convertView.getTag(); } ExamNotice notice=(ExamNotice) getItem(position); holder.studyPlanName.setText(notice.getNoticeTitle()); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd"); String noticeDate = sdf.format(notice.getNoticeDate()); holder.studyPlanDate.setText(noticeDate); return convertView; } private static class Holder{ public TextView studyPlanName,studyPlanDate; } }
看一下官方的API:
/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "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 an 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 two techniques: * - It reuses the convertView passed to getView() to avoid inflating View when it is 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() every 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 items in the list is determined by the number of speeches * in our array. * * @see android.widget.ListAdapter#getCount() */ public int getCount() { return DATA.length; } /** * Since the data comes from an array, just returning the index is * sufficent to get at the data. 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 references to children views to avoid unneccessary calls // to findViewById() on each row. ViewHolder holder; // When convertView is not null, we can reuse it directly, there is 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 two children views // we want to bind data 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; }
相关文章推荐
- Android之Surfaceview和SurfaceHolder用法
- Android知识——ViewHolder的作用与用法
- Android ViewHolder的作用与用法
- Android之ViewHolder用法
- Android ViewHolder的作用与用法
- Android ViewHolder的作用与用法 详解
- Android之ViewHolder用法
- Android ViewHolder的用法
- android之SurfaceView和SurfaceHolder用法
- Android ViewHolder的作用与用法
- Android ViewHolder的作用与用法
- Android之ViewHolder用法
- Android Google Maps onTap(int i)和onTap(GeoPoint geoPoint, MapView mapView)用法
- 【Android Training - Performance】提高显示布局文件的性能[Lesson 4 - 使用ViewHolder提升ListView的性能]
- android的UI中include、merge和viewstub用法
- android <viewStub />, <requestFocus />, <merge /> and <include />用法
- Android: TextView常用属性的用法详解
- android中用SurfaceHolder处理SurfaceView的画图
- Android隐喻(三) 图形绘制: Canvas、SurfaceView、Paint、Surface、SurfaceHolder、Bitmap
- Android中的自定义Adapter(继承自BaseAdapter)——与系统Adapter的调用方法一致——含ViewHolder显示效率的优化