010_02带缓存的图片查看器

　　第一次连接网络下载图片后，将在本机/data/data/...下保存图片；第二次打开应用程序点击“获取图片”将直接从本机缓存获取。

缓存图片保存位置如下：

MainActivity.java

package com.example.day10_02getpicturebycache;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

 

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
 
    final static int MSG_DOWNLOAD_OK =1; 
    final static int MSG_DOWNLOAD_ERROR =2; 

     Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            //针对message进行处理
            switch (msg.what) {
            case MSG_DOWNLOAD_OK:
                ImageView iv= (ImageView) findViewById(R.id.iv_pic);
                iv.setImageBitmap((Bitmap)msg.obj);
                break;
            case MSG_DOWNLOAD_ERROR:
                Toast.makeText(MainActivity.this, "下载失败", 1).show();
                break;    
            default:
                break;
            }         
        }    
    };

    public void getpicture(View v){
        File file = new File(getCacheDir(), "zy.jpg");
        if(file.exists()) {
            Bitmap bm =new BitmapFactory().decodeFile(file.getAbsolutePath());
            ImageView iv= (ImageView) findViewById(R.id.iv_pic);
            iv.setImageBitmap(bm);
        } 
        else {
            //下面的整个代码是从网络url下载对应的数据
            Thread tread = new Thread(){
                public void run() {
                        String path = "http://192.168.3.30:8080/tomcat.gif";
                        try {
                            URL url = new URL(path);
                            HttpURLConnection  conn = (HttpURLConnection) url.openConnection();
                            //set paramter 3
                            conn.setReadTimeout(5000);
                            conn.setRequestMethod("GET");
                            conn.setConnectTimeout(5000);
                            // pending;
                            conn.connect();
                            
                            if (conn.getResponseCode()==200) {
                              InputStream is = conn.getInputStream();
                              //如何放到缓存？
                              File file = new File(getCacheDir(), "zy.jpg");
                              FileOutputStream fos = new FileOutputStream(file);
                              byte[] b =new byte[1024];
                              int len=0;
                              while ((len=is.read(b))!=-1) {
                                fos.write(b, 0, len);
                              }
                              is.close();
                              fos.close();
              
                              //从一个保存的cache文件中，去得到一个bitmap对象。
                              Bitmap bm = new BitmapFactory().decodeFile(file.getAbsolutePath());

                              Message msg = handler.obtainMessage(); 
                              msg.what = MSG_DOWNLOAD_OK;
                              msg.obj  = bm;
                              handler.sendMessage(msg);
                              
                            }
                            else {
                              Message msg = handler.obtainMessage(); 
                              msg.what =MSG_DOWNLOAD_ERROR;
                              handler.sendMessage(msg);
                                //Toast.makeText(this, "下载失败", 1).show();
                            }    
                        }catch (Exception e) {
                            e.printStackTrace();
                        }
                };
            };
            tread.start();            
        }
    }
}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="hello_world" />
    <Button 
         android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="获取图片" 
        android:onClick="getpicture"/>
    <ImageView
        android:id="@+id/iv_pic"
         android:layout_width="wrap_content"
        android:layout_height="wrap_content"
         android:src="@drawable/ic_launcher"
        ></ImageView>
</LinearLayout>

AndroidManifest.xml中权限设置：

    <uses-permission android:name="android.permission.INTERNET"/>