Android热身:通过网络获取资源并更新UI组件

目标

点击“发送请求”按钮，下载某网页的html源码，并显示在TextView控件上；点击“清空”，清除TextView控件上的内容

效果图：

要点

开启网络权限
网络请求独立为一个模块
按钮点击事件的监听器
新开线程进行网络请求调用
用handler更新UI组件

源码

//MainActivity.java 主程序
package com.example.chris.handlerdemo;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity implements Button.OnClickListener {

    private TextView statusTextView;
    private Button btnDownload;
    private Button btnClean;

    //uiHandler在主线程中创建，所以自动绑定主线程
    private Handler uiHandler = new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        statusTextView = (TextView)findViewById(R.id.statusTextView);
        btnDownload = (Button)findViewById(R.id.btnDownload);
        btnDownload.setOnClickListener(this);

        btnClean = (Button)findViewById(R.id.btnClean);
        btnClean.setOnClickListener(this);
    }

    @Override
    public void onClick(View v){
        if(v==btnDownload){
            Thread downloadThread = new RockThread();
            downloadThread.start();
        }
        else if(v==btnClean){
            Thread cleanThread = new CleanThread();
            cleanThread.start();
        }
    }

    class CleanThread extends Thread{
        @Override
        public void run() {
            //btnClean.setText("");
            Runnable runnable = new Runnable(){
                @Override
                public void run(){
                    statusTextView.setText("");
                }
            };
            uiHandler.post(runnable);
        }
    }

    class RockThread extends Thread{
        @Override
        public void run(){
            String url = "http://218.244.143.208/index.html";
            final String response = NetUtils.get(url);
            uiHandler.post(new Runnable() {
                @Override
                public void run() {
                    statusTextView.setText(response);
                }
            });
        }
    }
}

//NetUtils.java 网络请求模块
package com.example.chris.handlerdemo;

import android.accounts.NetworkErrorException;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Created by chris on 2016/5/12.
 */

public class NetUtils {
    public static String post(String url, String content) {
        HttpURLConnection conn = null;
        try {
            // 创建一个URL对象
            URL mURL = new URL(url);
            // 调用URL的openConnection()方法,获取HttpURLConnection对象
            conn = (HttpURLConnection) mURL.openConnection();

            conn.setRequestMethod("POST");// 设置请求方法为post
            conn.setReadTimeout(5000);// 设置读取超时为5秒
            conn.setConnectTimeout(10000);// 设置连接网络超时为10秒
            conn.setDoOutput(true);// 设置此方法,允许向服务器输出内容

            // post请求的参数
            String data = content;
            // 获得一个输出流,向服务器写数据,默认情况下,系统不允许向服务器输出内容
            OutputStream out = conn.getOutputStream();// 获得一个输出流,向服务器写数据
            out.write(data.getBytes());
            out.flush();
            out.close();

            int responseCode = conn.getResponseCode();// 调用此方法就不必再使用conn.connect()方法
            if (responseCode == 200) {

                InputStream is = conn.getInputStream();
                String response = getStringFromInputStream(is);
                return response;
            } else {
                throw new NetworkErrorException("response status is "+responseCode);
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (conn != null) {
                conn.disconnect();// 关闭连接
            }
        }

        return null;
    }

    public static String get(String url) {
        HttpURLConnection conn = null;
        try {
            // 利用string url构建URL对象
            URL mURL = new URL(url);
            conn = (HttpURLConnection) mURL.openConnection();

            conn.setRequestMethod("GET");
            conn.setReadTimeout(5000);
            conn.setConnectTimeout(10000);

            int responseCode = conn.getResponseCode();
            if (responseCode == 200) {

                InputStream is = conn.getInputStream();
                String response = getStringFromInputStream(is);
                return response;
            } else {
                throw new NetworkErrorException("response status is "+responseCode);
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {

            if (conn != null) {
                conn.disconnect();
            }
        }

        return null;
    }

    private static String getStringFromInputStream(InputStream is)
            throws IOException {
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        // 模板代码 必须熟练
        byte[] buffer = new byte[1024];
        int len = -1;
        while ((len = is.read(buffer)) != -1) {
            os.write(buffer, 0, len);
        }
        is.close();
        String state = os.toString();// 把流中的数据转换成字符串,采用的编码是utf-8(模拟器默认编码)
        os.close();
        return state;
    }
}

//asynctask_activity.xml 布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/btnDown"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="下载图片" />

    <ImageView
        android:id="@+id/ivSinaImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
/>

</LinearLayout>