010_01网络图片查看器

package com.example.day10_01getpicture;

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.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主要用于异步消息的处理：当发出一个消息之后，首先进入一个消息队列，发送消息的函数即刻返回，
     *而另外一个部分逐个的在消息队列中将消息取出，然后对消息进行出来，就是发送消息和接收消息不是同步的处理。
     *这种机制通常用来处理相对耗时比较长的操作*/
     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){
        Thread tread = new Thread(){
            public void run() {
                //启动tomcat服务器
                String path = "http://192.168.3.39/tomcat.gif";
                try {
                    URL url = new URL(path);
                    HttpURLConnection  conn = (HttpURLConnection) url.openConnection();
                    conn.setReadTimeout(5000);
                    conn.setRequestMethod("GET");
                    conn.setConnectTimeout(5000);
                    // pending;
                    conn.connect();
                    
                    if (conn.getResponseCode()==200) {
                      InputStream is = conn.getInputStream();
                      Bitmap bm = new BitmapFactory().decodeStream(is);
                      
                     /*子线程内无法操作UI，原因？
                         ImageView iv= (ImageView) findViewById(R.id.iv_pic);
                      iv.setImageBitmap(bm); 
                       让主线程去更新ui--》 通知主线程去做事情，顺便把数据bm给到主线程
                       */  
                     // Message  msg = new Message();//ok
                      Message msg = handler.obtainMessage(); 
                      msg.what = MSG_DOWNLOAD_OK;
                      msg.obj  = bm;
                      handler.sendMessage(msg);                  
                    }
                    else {
                     // Message  msg = new Message();//!ok
                      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();    
    }
}

<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"
    tools:context="${relativePackage}.${activityClass}"
    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>

效果图：