（十二）网络图片查看器（注释更全面）

package com.example.networkviewimage;

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.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {
    protected static final int CHANGE_UI = 1;
    protected static final int ERROR = 2;
    public ImageView iv;
    public EditText et_path;

    // 创建消息处理器
    private Handler handler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            
            switch (msg.what) {
            case CHANGE_UI:
                iv.setImageBitmap((Bitmap) msg.obj);
                break;
            case ERROR:
                Toast.makeText(MainActivity.this, "获取图片失败", 0).show();
                break;

            }
        }

    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        iv = (ImageView) this.findViewById(R.id.iv);
        et_path = (EditText) this.findViewById(R.id.et_path);
    }

    public void click(View v) {
        final String path = et_path.getText().toString().trim();
        if (TextUtils.isEmpty(path)) {
            Toast.makeText(this, "网络图片的路径不能为空", 0).show();
        } else {
            // 连接服务器，获得图片。由于访问网络是个耗时的错误，所以必须在子线程中访问网络（在androi4.0以上的特性）
            new Thread(new Runnable() {

                @Override
                public void run() {
                    // TODO Auto-generated method stub
                    try {

                        URL url = new URL(path);
                        // 根据url发送http请求
                        HttpURLConnection conn = (HttpURLConnection) url
                                .openConnection();

                        conn.setConnectTimeout(5000); // 设置连接的超时时间
                        conn.setReadTimeout(5000); // 设置读数据的超时时间
                        conn.setRequestMethod("GET"); // 设置请求方式

                        int code = conn.getResponseCode(); // 得到服务器返回的响应码，200代表0K，404代表资源没有找到，503代表服务器内部错误
                        if (code == 200) {
                            InputStream is = conn.getInputStream(); // 从服务器获得的数据流，在此为从服务器获得图片
                            Bitmap bitmap = BitmapFactory.decodeStream(is); // 把流里面内容转化为Bitmap
                            // iv.setImageBitmap(bitmap);
                            // 告诉主线程，帮我更改界面，内容是bitmap
                            Message msg = new Message();
                            msg.what = CHANGE_UI;   
                            msg.obj = bitmap;

                            handler.sendMessage(msg);

                        } else {

                            Message msg = new Message();
                            msg.what = ERROR;

                            handler.sendMessage(msg);
                        }

                    } catch (Exception e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                        Message msg = new Message();
                        msg.what = ERROR;
                        handler.sendMessage(msg);
                        // Toast.makeText(MainActivity.this, "获取图片失败",
                        // 0).show();  土司也是UI，如果执行catch直接弹出Toast会出错
                    }
                }
            }).start();
        }

    }
}