最近写Adapter写得多了，慢慢就熟悉了。
用ViewHolder，主要是进行一些性能优化，减少一些不必要的重复操作。（WXD同学教我的。）
具体不分析了，直接上一份代码吧：
public class MarkerItemAdapter extends BaseAdapter
{
private Context mContext = null;
private List
public MarkerItemAdapter(Context context, List
{
mContext = context;
mMarkerData = markerItems;
}
public void setMarkerData(List
{
mMarkerData = markerItems;
}
@Override
public int getCount()
{
int count = 0;
if (null != mMarkerData)
{
count = mMarkerData.size();
}
return count;
}
@Override
public MarkerItem getItem(int position)
{
MarkerItem item = null;
if (null != mMarkerData)
{
item = mMarkerData.get(position);
}
return item;
}
@Override
public long getItemId(int position)
{
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
ViewHolder viewHolder = null;
if (null == convertView)
{
viewHolder = new ViewHolder();
LayoutInflater mInflater = LayoutInflater.from(mContext);
convertView = mInflater.inflate(R.layout.item_marker_item, null);
viewHolder.name = (TextView) convertView.findViewById(R.id.name);
viewHolder.description = (TextView) convertView
.findViewById(R.id.description);
viewHolder.createTime = (TextView) convertView
.findViewById(R.id.createTime);
convertView.setTag(viewHolder);
}
else
{
viewHolder = (ViewHolder) convertView.getTag();
}
// set item values to the viewHolder:
MarkerItem markerItem = getItem(position);
if (null != markerItem)
{
viewHolder.name.setText(markerItem.getName());
viewHolder.description.setText(markerItem.getDescription());
viewHolder.createTime.setText(markerItem.getCreateDate());
}
return convertView;
}
private static class ViewHolder
{
TextView name;
TextView description;
TextView createTime;
}
}
其中MarkerItem是自定义的类，其中包含name，description，createTime等字段，并且有相应的get和set方法。
ViewHolder是一个内部类，其中包含了单个项目布局中的各个控件。
单个项目的布局，即R.layout.item_marker_item如下：
xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:padding="5dp">
<TextView
android:id="@+id/name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Name"
android:textSize="20sp"
android:textStyle="bold" />
<TextView
android:id="@+id/description"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Description"
android:textSize="18sp" />
<TextView
android:id="@+id/createTime"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="CreateTime"
android:textSize="16sp" />
LinearLayout>
官方的API Demos中也有这个例子：
package com.example.android.apis.view中的List14：
/*
* 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;
}
其中布局：
xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView android:id="@+id/icon"
android:layout_width="48dip"
android:layout_height="48dip" />
<TextView android:id="@+id/text"
android:layout_gravity="center_vertical"
android:layout_width="0dip"
android:layout_weight="1.0"
android:layout_height="wrap_content" />
LinearLayout>
更多关于Adapter优化的文章：
http://www.cnblogs.com/over140/archive/2011/03/23/1991100.html
http://www.cnblogs.com/halzhang/archive/2010/12/05/1896791.html