【Android 开发】：UI控件之 ImageView 从网络上获取图像

    在我们的手机应用开发中，经常要进行客户端与服务端之间的交互，我们可能会从网络上获取一张图像显示在我们的手机上，这样我们可以使用HTTP协议进行操作。这一讲我们将学习如何从服务端获取图片到手机客户端

    案例：点击按钮从网络上获取ImageView图像显示在本地

程序实现：

1. 布局文件

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <ImageView        android:id="@+id/imageView"        android:layout_width="wrap_content"        android:layout_height="wrap_content" />    <Button         android:id="@+id/button"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="下载网络图片"/>        </LinearLayout>

2. 程序主要代码

1)HttpUtils.java 作为辅助类

public class HttpUtils {    private final static String URL_PATH = "http://www.android.com/images/about/about-nexus-family.png"; //访问网络图片的路径        public HttpUtils() {        // TODO Auto-generated constructor stub    }        /**     * 从网络中获取图片信息，以流的形式返回     * @return     * @throws IOException      */    public static InputStream getImageViewInputStream() throws IOException{                InputStream inputStream = null;            URL url = new URL(URL_PATH);            if(url != null){                HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();                httpURLConnection.setConnectTimeout(3000); //设置连接超时的时间                httpURLConnection.setRequestMethod("GET");                httpURLConnection.setDoInput(true);                //设置响应的代码                int response_code = httpURLConnection.getResponseCode();                if(response_code == 200){                    inputStream = httpURLConnection.getInputStream();                }            }                return inputStream;    }        public static byte[] getImageViewArray(){        byte[] data = null;        InputStream inputStream = null;                //不需要关闭输出流，直接 写入到内存中        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();        try {            URL url = new URL("URL_PATH");            if(url != null){                HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();                httpURLConnection.setConnectTimeout(3000); //设置连接超时的时间                httpURLConnection.setRequestMethod("GET");                httpURLConnection.setDoInput(true);                //设置响应的代码                int response_code = httpURLConnection.getResponseCode();                                int len = 0;                byte[] b_data = new byte[1024];                if(response_code == 200){                    inputStream = httpURLConnection.getInputStream();                    while((len = inputStream.read(b_data)) != -1) {                        outputStream.write(b_data, 0, len);                    }                    data = outputStream.toByteArray();                }            }        } catch (Exception e) {            // TODO: handle exception        }finally{            if(inputStream != null){                try {                    inputStream.close();                } catch (IOException e) {                    // TODO Auto-generated catch block                    e.printStackTrace();                }            }        }                return data;            }}

2) 主程序

public class ImageViewDemo extends Activity {    private Button button;    private ImageView imageView;        /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        initComponent();        button.setOnClickListener(new View.OnClickListener() {                        @Override            public void onClick(View v) {                // TODO Auto-generated method stub                new Thread(){                                        public void run() {                                                try {                            InputStream inputStream = HttpUtils.getImageViewInputStream();                            Bitmap bitmap = BitmapFactory.decodeStream(inputStream);                            imageView.setImageBitmap(bitmap); //需要一个Bitmap对象，可以从 BitmapFactory工厂中获得                                                    } catch (IOException e) {                            // TODO: handle exception                        }                    };                }.start();            }        });            }        private void initComponent(){        button = (Button)findViewById(R.id.button);        imageView = (ImageView)findViewById(R.id.imageView);    }}

[注意编程规范]: 如果方法A里面含有了 try catch模块来捕获异常，在方法B中调用A的过程中也需要try catch 一次异常。则这种情况下一般要把A的异常抛出，让方法B去捕获这个异常。

   访问网络的主程序最好另起一个线程而不是写在UI主线程中。