Android异步加载图片详解之方式一(1)

MainActivity.java如下:

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();	
		}
    	
    }
    
}

ListViewAdapter.java如下:

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;
	}
}

ListViewItem.java如下:

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;
	}

}

 main.xml如下:

<?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>

listviewitem.xml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="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>