看过好多资料，原来对Handler&Message&looper&Runnable多线程一知半解，现在写了个demo’，认真分析理解了一下，帮助大家把这几个知识点连贯的串一下，希望对大家有所帮助。
自Android2.3以后，谷歌官方规定，耗时的任务不能在主线程出现，会严重影响用户的体验，其实就算谷歌不提出，有经验的程序员也不会把耗时任务放在主线程的，这样会给用户造成一个假死的现象，所以一引入了Handler。Looper虽然大家看不到，但是却有至关重要的作用
@Overridepublic void onClick(View v) {// TODO Auto-generated method stubswitch (v.getId()) {// 登录case R.id.login_btn_login://主线程，在looper中进行循环执行mDialog = new ProgressDialog(LoginDemoActivity.this);mDialog.setTitle("登陆");mDialog.setMessage("正在登陆服务器，请稍后…");mDialog.show();
//子线程，，开始执行LoginThread线程类Thread loginThread = new Thread(new LoginThread());loginThread.start();break;// 注册case R.id.login_btn_zhuce:Intent intent = new Intent();intent.setClass(LoginDemoActivity.this, RegisterActivity.class);startActivity(intent);default:break;}}
// LoginThread线程类class LoginThread implements Runnable {@Overridepublic void run() {String username = inputUsername.getText().toString();String password = inputPassword.getText().toString();boolean checkstatus = sp.getBoolean("checkstatus", false);if (checkstatus) {// 获取已经存在的用户名和密码String realUsername = sp.getString("username", "");String realPassword = sp.getString("password", "");if ((!realUsername.equals("")) && !(realUsername == null)|| (!realPassword.equals(""))|| !(realPassword == null)) {if (username.equals(realUsername)&& password.equals(realPassword)) {username = inputUsername.getText().toString();password = inputPassword.getText().toString();}}} else {password = password;}// URL合法，但是这一步并不验证密码是否正确boolean loginValidate = false;try {loginValidate = loginServer(username, password);} catch (UnsupportedEncodingException e) {// TODO Auto-generated catch blocke.printStackTrace();}//下面代码将message放入looper消息队列中，一个looper可以有多个message队列，但是一个message只能对应一个looperMessage msg = handler.obtainMessage();if (loginValidate) {
//根据返回不同的结果赋给msg不同的值if (responseMsg.equals("0")) {msg.what = 0;handler.sendMessage(msg);} else {msg.what = 1;handler.sendMessage(msg);}} else {msg.what = 2;handler.sendMessage(msg);}}}
// Handler，根据不同的message的值，执行不同的请求Handler handler = new Handler() {public void handleMessage(Message msg) {switch (msg.what) {case 0:mDialog.cancel();Toast.makeText(getApplicationContext(), "登录成功！",Toast.LENGTH_SHORT).show();Intent intent = new Intent();intent.setClass(LoginDemoActivity.this, MainActivity.class);startActivity(intent);finish();break;case 1:mDialog.cancel();Toast.makeText(getApplicationContext(), "密码错误",Toast.LENGTH_SHORT).show();break;case 2:mDialog.cancel();Toast.makeText(getApplicationContext(), "URL验证失败",Toast.LENGTH_SHORT).show();break;}}
与其在那里苦苦挣扎，碍于面子硬撑，倒不如微笑着面对，
