Android中Handler消息传递机制

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因为是在项目中的收获，所以不全，以后遇到其他的我会加上。

安卓中用Handler机制来实现主线程和子线程之间的通信，通信的媒介是Message的实例。

首先要在主线程声明一个Handler对象，然后重写里面的handMessage（Message msg）方法，用switch-case语句进行匹配处理

在子线程中，new一个Message实例msg，可以填写msg.what和msg.object，类似一个map对象，用主线程中的handler的handleMessage（msg）handler的handleMessage（msg)

private Handler handler = new Handler() {@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);switch (msg.what) {case ENTER_HOME:Toast.makeText(getApplicationContext(), "进入界面", 0).show();break;case UPDATE:Toast.makeText(getApplicationContext(), "更新", 0).show();break;case NET_ERROR:Toast.makeText(getApplicationContext(), "网络未连接", 0).show();break;case READ_ERROR:Toast.makeText(getApplicationContext(), "流读取失败", 0).show();break;case JSON_ERROR:Toast.makeText(getApplicationContext(), "json读取失败", 0).show();break;}}};

<span style="font-family: Arial, Helvetica, sans-serif;">private void checkUpdate() {</span>

// TODO Auto-generated method stubnew Thread(){public void run() {Message msg = new Message();long startTime = System.currentTimeMillis();try {URL url = new URL("..");HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setReadTimeout(5000);int code = conn.getResponseCode();if(code==200) {InputStream is = conn.getInputStream();String json = StreamTools.readFromStream(is);JSONObject obj = new JSONObject(json);verson = obj.getString("verson");description = obj.getString("description");apkUrl = obj.getString("apkUrl");if(getVerson().equals(verson)) {//进入主界面msg.what = ENTER_HOME;} else {//更新msg.what = UPDATE;}}} catch (MalformedURLException e) {// TODO Auto-generated catch blocke.printStackTrace();msg.what = NET_ERROR;} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();msg.what = READ_ERROR;} catch (JSONException e) {// TODO Auto-generated catch blocke.printStackTrace();msg.what = JSON_ERROR;}finally{long endTime = System.currentTimeMillis();long dTime = startTime - endTime;if(dTime < 2000) {try {Thread.sleep(2000 - dTime);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}handler.sendMessage(msg);}};}.start();}

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