Android 网络图片查看器

由于android下的网络连接不能在主线程操作，另外UI的改变也只能通过主线程来变化，所以一般来说操作网络我们都要开启一个子线程执行，而UI的改变则通过handler消息传递给主线程，委托主线程操作。

以下是一个android网络图片查看器，需要传入一个URL地址来查看该图片：

package com.wuyou.webimgbrowser;





import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.support.v7.app.ActionBarActivity;

import android.text.TextUtils;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.ImageView;

import android.widget.Toast;



import java.io.InputStream;

import java.net.HttpURLConnection;

import java.net.URL;



public class MainActivity extends ActionBarActivity {



    //常量：改变显示的图片

    private static final int CHANGE_IMG = 1;

    private static final int ERROR = 2;



    private ImageView imageView;

    private EditText editText;

    private Button button;



    //消息处理器

    private Handler handler = new Handler() {

        @Override

        public void handleMessage(Message msg) {

            if (msg.what == CHANGE_IMG) {

                Bitmap bitmap = (Bitmap) msg.obj;

                imageView.setImageBitmap(bitmap);

            } else if (msg.what == ERROR) {

                Toast.makeText(MainActivity.this, "获取图片失败！", Toast.LENGTH_LONG).show();

            }

        }

    };



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);



        imageView = (ImageView) findViewById(R.id.iv);

        editText = (EditText) findViewById(R.id.et);

        button = (Button) findViewById(R.id.bt);



    }



    public void click(View view) {

        final String path = editText.getText().toString().trim();



        //子线程不能修改UI，只能通过消息发送到主线程，让主线程代替修改UI

        new Thread(new Runnable() {

            @Override

            public void run() {

                if (TextUtils.isEmpty(path)) {

                    sendError(null);

                } else {

                    try {

                        System.out.println("path = " + path);

                        URL url = new URL(path);

                        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();

                        httpURLConnection.setRequestMethod("GET");//设置以get方式获取资源

                        httpURLConnection.setConnectTimeout(5000);//设置连接服务器如果没有在5秒钟运行则抛出错误

                        httpURLConnection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:22.0) Gecko/20100101 Firefox/22.0");

                        if (httpURLConnection.getResponseCode() == 200) {

                            InputStream inputStream = httpURLConnection.getInputStream();

                            Bitmap bitmap = BitmapFactory.decodeStream(inputStream);

                            Message message = new Message();

                            message.what = CHANGE_IMG;

                            message.obj = bitmap;

                            handler.sendMessage(message);

                        } else {

                            sendError(null);

                        }

                    } catch (Exception e) {

                        sendError(e);

                    }

                }

            }



            //发送错误

            private void sendError(Exception e) {

                if (e != null) {

                    e.printStackTrace();

                }

                Message message = new Message();

                message.what = ERROR;

                handler.sendMessage(message);

            }

        }).start();

    }





}

其中布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:id="@+id/container"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity"

    android:orientation="vertical"

    tools:ignore="MergeRootFrame">



    <ImageView

        android:id="@+id/iv"

        android:layout_weight="3000"

        android:layout_height="match_parent"

        android:layout_width="match_parent" />



    <EditText

        android:text="http://image.sjrjy.com/201011/291354164ea84578066309.jpg"

        android:lines="1"

        android:id="@+id/et"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content" />



    <Button

        android:id="@+id/bt"

        android:text="浏览图片"

        android:onClick="click"

        android:layout_height="wrap_content"

        android:layout_width="wrap_content" />



</LinearLayout>

最后不要忘了在清单文件添加：（网络连接的权限）

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