本文章是学习尚硅谷android系列视频中的《消息机制与异步任务》章节所记载的笔记。
Message:消息
- 可理解为线程间通讯的数据单元,可通过message携带需要的数据
- 创建对象:Message.obtain(what)
- 封装数据:
public int what //id标识
public int arg1
public int arg2
public Object obj
Handler:处理器
- Handler是Message的处理器,同时也负责消息的发送和移除工作
- 发送即时消息:sendMessage(Message msg)
- 发送延时消息:sendMessageDelayed(Message msg,long time)(实际是延时处理不是延时发送)
- 处理消息:handleMessage(Message msg)(回调方法)
- 移除还未处理的消息:removeMessages(int what)
MessageQueue:消息队列
- 用来存放通过Handler发送的消息
- 它是一个按Message的when排序的优先级队列
Looper(钩子):循环器
- 负责循环取出MessageQueue里面的当前需要处理的Message
- 交给对应的Handler进行处理
- 处理完后,将Message缓存到消息池中,以备复用
Handler的基本使用步骤:
- 创建Handler成员变量对象,并重写handleMessage(Message msg)方法
- 在分/主线程创建Message对象
- 使用Handler对象发送Message
- 在handleMessage(Message msg)中处理消息
activity代码:
import android.annotation.SuppressLint;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.HashMap;
public class MainActivity extends AppCompatActivity {
private String address = "https://www.sojson.com/open/api/weather/json.shtml?";
ProgressDialog progressDialog;
private Button button;
private TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initViews();
}
private void initViews(){
progressDialog = new ProgressDialog(this);
progressDialog.setTitle("加载中...");
progressDialog.setCancelable(true);
textView = findViewById(R.id.textView);
button = findViewById(R.id.button);
button.setOnClickListener(onClickListener);
}
View.OnClickListener onClickListener = new View.OnClickListener() {
@Override
public void onClick(View v) {
switch (v.getId()){
case R.id.button:
getWeather();
break;
}
}
};
@SuppressLint("HandlerLeak")
Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
if(progressDialog != null && progressDialog.isShowing()){
progressDialog.dismiss();
}
textView.setText(msg.getData().getString("weather"));
}
};
private void getWeather(){
progressDialog.show();
new Thread(new Runnable() {
@Override
public void run() {
HashMap<String,String> map = new HashMap<>();
map.put("city","成都");
String result = HttpNetTool.requestGet(map,address);
Message message = Message.obtain(handler,1);
Bundle bundle = new Bundle();
bundle.putString("weather",result);
message.setData(bundle);
handler.sendMessage(message);
}
}).start();
}
}
xml代码:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="16dp"
android:text="TextView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/button" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="获取天气"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
权限:
<uses-permission android:name="android.permission.INTERNET"/>
Handler的小DEMO:
Activity代码:
package com.atguigu.l05_handler;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
/**
* 使用Handler的小DEMO
* @author 张晓飞
1. 手动增加/减少
2. 自动增加/减少
3. 限制数字的最大和最小值 [1,20]
4. 限制Button可操作性
*/
public class HandlerDemoActivity extends Activity implements OnClickListener {
private static final int WHAT_INCREASE = 1;
private static final int WHAT_DECREASE = 2;
private TextView tv_demo_number;
private Button btn_demo_increase;
private Button btn_demo_decrease;
private Button btn_demo_pause;
private Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
//得到当前显示的数值
int number = Integer.parseInt(tv_demo_number.getText().toString());
switch (msg.what) {
case WHAT_INCREASE:
//限制number<=20
if(number==20) {
//设置暂停不能操作
btn_demo_pause.setEnabled(false);
Toast.makeText(HandlerDemoActivity.this, "已经达到最大值", 0).show();
return;
}
number++;
tv_demo_number.setText(number+"");
//发送增加的延迟消息
handler.sendEmptyMessageDelayed(WHAT_INCREASE, 1000);
break;
case WHAT_DECREASE:
//限制number>=1
if(number==1) {
//设置暂停不能操作
btn_demo_pause.setEnabled(false);
Toast.makeText(HandlerDemoActivity.this, "已经达到最小值", 0).show();
return;
}
number--;
tv_demo_number.setText(number+"");
//发送减少的延迟消息
handler.sendEmptyMessageDelayed(WHAT_DECREASE, 1000);
break;
default:
break;
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_handler_demo);
init();
}
private void init() {
tv_demo_number = (TextView) findViewById(R.id.tv_demo_number);
btn_demo_increase = (Button) findViewById(R.id.btn_demo_increase);
btn_demo_decrease = (Button) findViewById(R.id.btn_demo_decrease);
btn_demo_pause = (Button) findViewById(R.id.btn_demo_pause);
btn_demo_increase.setOnClickListener(this);
btn_demo_decrease.setOnClickListener(this);
btn_demo_pause.setOnClickListener(this);
}
@Override
public void onClick(View v) {
if(v==btn_demo_increase) {//自动增加 what =1
//限制Button可操作性
btn_demo_increase.setEnabled(false);
btn_demo_decrease.setEnabled(true);
btn_demo_pause.setEnabled(true);
//停止减少(移除未处理的减少的消息)
handler.removeMessages(WHAT_DECREASE);
//发消息(增加)
handler.sendEmptyMessage(WHAT_INCREASE);
} else if(v==btn_demo_decrease) {//自动减少 what=2
//限制Button可操作性
btn_demo_increase.setEnabled(true);
btn_demo_decrease.setEnabled(false);
btn_demo_pause.setEnabled(true);
//停止增加(移除未处理的增加的消息)
handler.removeMessages(WHAT_INCREASE);
//发消息(减少)
handler.sendEmptyMessage(WHAT_DECREASE);
} else if(v==btn_demo_pause) {//暂停
//限制Button可操作性
btn_demo_increase.setEnabled(true);
btn_demo_decrease.setEnabled(true);
btn_demo_pause.setEnabled(false);
//停止增加/减少(移除未处理的减少/增加的消息)
handler.removeMessages(WHAT_INCREASE);
handler.removeMessages(WHAT_DECREASE);
}
}
}
XML代码:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/tv_demo_number"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="10"
android:textColor="#ff0000"
android:textSize="20sp"/>
<Button
android:id="@+id/btn_demo_increase"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="自动增加" />
<Button
android:id="@+id/btn_demo_decrease"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="自动减少" />
<Button
android:id="@+id/btn_demo_pause"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="暂停"
android:enabled="false"/>
</LinearLayout>
Handler原理:
源码简单解析:
Message:
属性:
- public int what;//标识(id)
- public int arg1;//保存int数据
- public int arg2;//保存int数据
- public Object obj;//保存任意数据
- long when;//记录应该被处理的时间值
- Handler target;//处理message的handler的引用,也就是发消息的handler
- Runnable callback;//用来处理消息的回调器
- Message next;//指向下一个Message,用来形成一个链表
- private static Message sPool;//用来缓存处理过的Message对象,以便复用
方法:
- public static Message obtain();//它利用了Message中的消息池(sPool)
Handler:
方法:
- sendMessage(Message msg);//发送即时消息
- sendMessageDelayed(Message msg,long delayMillis);//发送延时消息
- sendEmptyMessage(int what);//发送即时得空消息
- sendEmptyMessageDelayed(int what,long delayMillis);//发送空的延时消息
- sendMessageAtTime(Message msg,long uptimeMillis);//
- removeMessages(int what);//移除还未处理的消息
- handleMessage(Message msg);//处理消息的回调
MessageQueue:
方法:
- enqueueMessage(Message msg,long when);//将Message添加到队列中,根据when来排序
Looper:
方法:
- loop();//核心方法
final Looper me = myLooper();//得到Looper对象
final MessageQueue queue = me.mQueue;//得到消息对列对象
for(;;){
Message msg = queue.next();//可能处于等待状态,但是不会阻塞主线程
......
msg.target.dispatchMessage(msg);//调用Handler去分发消息,并处理消息
msg.recycle();//回收message
}