Handler&Looper&Message&Runnable多线程

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http://blog.csdn.net/qq_23195583/article/details/44221401

@Override
public void onClick(View v) {
// TODO Auto-generated method stub


switch (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 {


@Override
public 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 block
e.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looper
Message 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;


}


}