android 网络图片查看器，Handler的用法

通过网络访问图片，并通过Handler更新主线程的控件。

public class MainActivity extends Activity {protected static final String TAG = "MainActivity";private Button btn_photo;private ImageView iv_photo;private EditText et_url;private Handler handler = new Handler(){@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);Log.i(TAG, " 消息 ： " + msg);if (msg.what == 0) {iv_photo.setImageBitmap((Bitmap) msg.obj);}else if (msg.what == 1) {Toast.makeText(MainActivity.this, "抓取失败", 0).show();}}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);iv_photo = (ImageView) findViewById(R.id.iv_photo);et_url = (EditText) findViewById(R.id.et_photo);btn_photo = (Button) findViewById(R.id.btn_go);btn_photo.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {final String uri = et_url.getText().toString();new Thread(new Runnable() {@Overridepublic void run() {Bitmap bitmap = getImageFromNet(uri);if (bitmap != null) {Message msg = new Message();msg.what = 0;msg.obj = bitmap;handler.sendMessage(msg);}else if (bitmap == null) {Message msg = new Message();msg.what = 1;handler.sendMessage(msg);}}}).start();//				iv_photo.setImageBitmap(bitmap);}});}private Bitmap getImageFromNet(String url){HttpURLConnection conn = null;try {URL mURL = new URL(url); //创建一个URL对象//创建一个http连接对象conn = (HttpURLConnection) mURL.openConnection();conn.setRequestMethod("GET");  //采用get的方法请求数据conn.setConnectTimeout(10*1000);  //设置10s的连接超时conn.setReadTimeout(5*1000);  //读取超时conn.connect(); //开始连接int responseCode = conn.getResponseCode();if (responseCode == 200) {//访问成功InputStream is = conn.getInputStream();Bitmap bitmap = BitmapFactory.decodeStream(is);return bitmap;}else {Toast.makeText(this, "访问失败", 0).show();}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}finally{//断开连接conn.disconnect();}return null;}}

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