Android异步加载图片详解之方式一(1)

package cn.ideallistview;
import java.util.ArrayList;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ListView;
//ListView中的Item显示一张网络图片
//流程:
//1 试图从内存的缓存中获取
//  1.1从一级缓存(强引用)中查找图片
//  1.2从二级缓存(若引用)中查找图片
//  若1失败转入2
//2 试图从SDCard的File中获取
//  若2失败转入3
//3 从网络下载图片
//  3.1将下载后的图片保存至SDCard的File中
//  3.2将从SDCard的File中获取的图片返回给ListView显示
//  3.3将从SDCard的File中获取的图片保存至内存的缓存
//     3.3.1若一级缓存剩余空间足够保存该图片则保存至一级缓存
//          若失败转入3.3.2
//     3.3.2将一级缓存中最陈旧的元素放入二级缓存.
//          再次核实一级缓存存剩余空间,直至有足够空间存放图片

public class MainActivity extends Activity {

ListView listView;
ListViewAdapter adapter;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
initView();
}

public void initView() {
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new ButtonOnClickListener());

listView = (ListView) findViewById(R.id.listView);
ArrayList<ListViewItem> arrayList = new ArrayList<ListViewItem>();

ListViewItem item1 = new ListViewItem
("xxxx","http://images.csdn.net/20121018/zazhi-68-78-1018.jpg");
arrayList.add(item1);

ListViewItem item2 = new ListViewItem
("xxxx","http://info-database.csdn.net/Upload/2012-10-08/zazhi-210-90-1008.jpg");
arrayList.add(item2);

ListViewItem item3 = new ListViewItem
("xxxx","http://images.csdn.net/20121119/20111211223655841.jpg");
arrayList.add(item3);

ListViewItem item4 = new ListViewItem
("xxxx","http://images.csdn.net/20121119/20120619174604972.jpg");
arrayList.add(item4);

ListViewItem item5 = new ListViewItem
("xxxx","http://csdnimg.cn/www/images/pic_foot_report110.png");
arrayList.add(item5);

ListViewItem item6 = new ListViewItem
("xxxx","http://csdnimg.cn/www/images/pic_foot_report.png");
arrayList.add(item6);

ListViewItem item7 = new ListViewItem
("xxxx","http://csdnimg.cn/www/images/pic_foot_BNIA.png");
arrayList.add(item7);

ListViewItem item8 = new ListViewItem
("xxxx","http://csdnimg.cn/www/images/pic_foot_gongshang.png");
arrayList.add(item8);

ListViewItem item9 = new ListViewItem
("xxxx","http://images.csdn.net/20120803/logo-qixing02.jpg");
arrayList.add(item9);

ListViewItem item10 = new ListViewItem
("xxxx","http://images.csdn.net/20120726/quanjing-logo-shouye.jpg");
arrayList.add(item10);

ListViewItem item11 = new ListViewItem
("xxxx","http://images.csdn.net/20120726/nhn-logo-shouye.jpg");
arrayList.add(item11);

ListViewItem item12 = new ListViewItem
("xxxx","http://images.csdn.net/20120510/shanghai-jiaoda-logo.jpg");
arrayList.add(item12);

ListViewItem item13 = new ListViewItem
("xxxx","http://images.csdn.net/20120312/bigman2.gif");
arrayList.add(item13);

ListViewItem item14 = new ListViewItem
("xxxx","http://images.csdn.net/20120216/csdn2.gif");
arrayList.add(item14);

ListViewItem item15 = new ListViewItem
("xxxx","http://images.csdn.net/20121109/win8_100x74.jpg");
arrayList.add(item15);

ListViewItem item16 = new ListViewItem
("xxxx","http://images.csdn.net/20120816/cf-20120816.jpg");
arrayList.add(item16);

ListViewItem item17 = new ListViewItem
("xxxx","http://images.csdn.net/20120704/bi05.jpg");
arrayList.add(item17);

ListViewItem item18 = new ListViewItem
("xxxx","http://images.csdn.net/20120816/amd-20120816.jpg");
arrayList.add(item18);

ListViewItem item19 = new ListViewItem
("xxxx","http://y2.ifengimg.com/2012/12/08/09383369.jpg");
arrayList.add(item19);

ListViewItem item20 = new ListViewItem
("xxxx","http://y1.ifengimg.com/2012/12/08/09320040.jpg");
arrayList.add(item20);

ListViewItem item21 = new ListViewItem
("xxxx","http://y3.ifengimg.com/4ccd6020154f55cb/2012/1207/2.jpg");
arrayList.add(item21);

ListViewItem item22 = new ListViewItem
("xxxx","http://y2.ifengimg.com/2012/12/08/09425571.jpg");
arrayList.add(item22);

ListViewItem item23 = new ListViewItem
("xxxx","http://y2.ifengimg.com/b19fadab6fcc0645/2012/1011/123.jpg");
arrayList.add(item23);

ListViewItem item24 = new ListViewItem
("xxxx","http://y2.ifengimg.com/2012/11/15/07414772.jpg");
arrayList.add(item24);

ListViewItem item25 = new ListViewItem
("xxxx","http://y2.ifengimg.com/2012/11/15/07532374.jpg");
arrayList.add(item25);

ListViewItem item26 = new ListViewItem
("xxxx","http://y0.ifengimg.com/2012/11/15/07583017.jpg");
arrayList.add(item26);

ListViewItem item27 = new ListViewItem
("xxxx","http://y0.ifengimg.com/2012/02/20/14175732.jpg");
arrayList.add(item27);

ListViewItem item28 = new ListViewItem
("xxxx","http://y2.ifengimg.com/2012/10/29/21175274.jpg");
arrayList.add(item28);

ListViewItem item29 = new ListViewItem
("xxxx","http://res.news.ifeng.com/2727e09814adca26/2011/1221/rdn_4ef0fb0333564.jpg");
arrayList.add(item29);

ListViewItem item30 = new ListViewItem
("xxxx","http://y1.ifengimg.com/2012/12/04/10060551.jpg");
arrayList.add(item30);

ListViewItem item31 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec068537d8f6.jpg");
arrayList.add(item31);

ListViewItem item32 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec068554fa3f.jpg");
arrayList.add(item32);

ListViewItem item33 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec06853bd85b.jpg");
arrayList.add(item33);

ListViewItem item34 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec06854ace88.jpg");
arrayList.add(item34);

ListViewItem item35 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec06855bad01.jpg");
arrayList.add(item35);

ListViewItem item36 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec0685649c4e.jpg");
arrayList.add(item36);

ListViewItem item37 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec068562ac3d.jpg");
arrayList.add(item37);

ListViewItem item38 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec06854dc836.jpg");
arrayList.add(item38);

ListViewItem item39 = new ListViewItem
("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec06855ef0ea.jpg");
arrayList.add(item39);

//		ListViewItem item40 = new ListViewItem
//		("xxxx","http://res.news.ifeng.com/b77953a0c6aae8fb/2011/1114/rdn_4ec068568beda.jpg");
//		arrayList.add(item40);
ListViewItem item40 = new ListViewItem
("xxxx","http://s12.sinaimg.cn/middle/4b181bd0gbf6cb07c2a1b&690");
arrayList.add(item40);

adapter = new ListViewAdapter(arrayList, MainActivity.this);

listView.setAdapter(adapter);
}

@Override
public void onDestroy()
{
listView.setAdapter(null);
super.onDestroy();
}

private class ButtonOnClickListener implements OnClickListener{
@Override
public void onClick(View v) {
adapter.imageLoader.clearCache();
//adapter.notifyDataSetChanged();
}

}

}

package cn.ideallistview;
import java.util.ArrayList;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import cn.loadImages.ImageLoader;

public class ListViewAdapter extends BaseAdapter {
private static LayoutInflater inflater=null;
public ImageLoader imageLoader;
private ArrayList<ListViewItem> mArrayList;
private Context mContext;
public ListViewAdapter(ArrayList<ListViewItem> mArrayList,Context mContext) {
super();
this.mArrayList = mArrayList;
this.mContext = mContext;
inflater=(LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
imageLoader=new ImageLoader(mContext);
}

public int getCount() {
if (mArrayList==null) {
return 0;
} else {
return mArrayList.size();
}

}

public Object getItem(int position) {
if (mArrayList==null) {
return null;
} else {
return mArrayList.get(position);
}
}

public long getItemId(int position) {
return position;
}

public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder=null;
if (convertView==null) {
holder=new ViewHolder();
convertView=inflater.inflate(R.layout.listviewitem, null, false);
holder.textView=(TextView) convertView.findViewById(R.id.textView);
holder.imageView=(ImageView) convertView.findViewById(R.id.imageView);
convertView.setTag(holder);
} else {
holder=(ViewHolder) convertView.getTag();
}

if (this.mArrayList!=null) {
ListViewItem listViewItem=this.mArrayList.get(position);
if (holder.textView!=null) {
holder.textView.setText(listViewItem.getContent());
}
if (holder.imageView!=null) {
try {
String imageUrl=listViewItem.getImageURL();
//加载网络上的图片
imageLoader.displayImage(imageUrl, holder.imageView);
} catch (Exception e) {
e.printStackTrace();
}
}
}
return convertView;

}

private class ViewHolder{
ImageView imageView;
TextView textView;
}
}

package cn.ideallistview;
public class ListViewItem {
String content;
String imageURL;

public ListViewItem(String content, String imageURL) {
super();
this.content = content;
this.imageURL = imageURL;
}

public String getContent() {
return content;
}

public void setContent(String content) {
this.content = content;
}

public String getImageURL() {
return imageURL;
}

public void setImageURL(String imageURL) {
this.imageURL = imageURL;
}

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ListView
android:id="@+id/listView"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1"/>
<Button
android:id="@+id/button"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Clear FileCache"/>
</LinearLayout>

<?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="wrap_content">
<ImageView
android:id="@+id/imageView"
android:layout_width="50dip"
android:layout_height="50dip"
android:src="@drawable/stub"
android:scaleType="centerCrop"/>
<TextView
android:id="@+id/textView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:layout_gravity="left|center_vertical"
android:textSize="20dip"
android:layout_marginLeft="10dip"/>
</LinearLayout>