本文章是學習尚硅谷android系列視頻中的《消息機制與異步任務》章節所記載的筆記。
Message:消息
- 可理解爲線程間通訊的數據單元,可通過message攜帶需要的數據
- 創建對象:Message.obtain(what)
- 封裝數據:
public int what //id標識
public int arg1
public int arg2
public Object obj
Handler:處理器
- Handler是Message的處理器,同時也負責消息的發送和移除工作
- 發送即時消息:sendMessage(Message msg)
- 發送延時消息:sendMessageDelayed(Message msg,long time)(實際是延時處理不是延時發送)
- 處理消息:handleMessage(Message msg)(回調方法)
- 移除還未處理的消息:removeMessages(int what)
MessageQueue:消息隊列
- 用來存放通過Handler發送的消息
- 它是一個按Message的when排序的優先級隊列
Looper(鉤子):循環器
- 負責循環取出MessageQueue裏面的當前需要處理的Message
- 交給對應的Handler進行處理
- 處理完後,將Message緩存到消息池中,以備複用
Handler的基本使用步驟:
- 創建Handler成員變量對象,並重寫handleMessage(Message msg)方法
- 在分/主線程創建Message對象
- 使用Handler對象發送Message
- 在handleMessage(Message msg)中處理消息
activity代碼:
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("加載中...");
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代碼:
<?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="獲取天氣"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
權限:
<uses-permission android:name="android.permission.INTERNET"/>
Handler的小DEMO:
Activity代碼:
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 張曉飛
1. 手動增加/減少
2. 自動增加/減少
3. 限制數字的最大和最小值 [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) {
//得到當前顯示的數值
int number = Integer.parseInt(tv_demo_number.getText().toString());
switch (msg.what) {
case WHAT_INCREASE:
//限制number<=20
if(number==20) {
//設置暫停不能操作
btn_demo_pause.setEnabled(false);
Toast.makeText(HandlerDemoActivity.this, "已經達到最大值", 0).show();
return;
}
number++;
tv_demo_number.setText(number+"");
//發送增加的延遲消息
handler.sendEmptyMessageDelayed(WHAT_INCREASE, 1000);
break;
case WHAT_DECREASE:
//限制number>=1
if(number==1) {
//設置暫停不能操作
btn_demo_pause.setEnabled(false);
Toast.makeText(HandlerDemoActivity.this, "已經達到最小值", 0).show();
return;
}
number--;
tv_demo_number.setText(number+"");
//發送減少的延遲消息
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) {//自動增加 what =1
//限制Button可操作性
btn_demo_increase.setEnabled(false);
btn_demo_decrease.setEnabled(true);
btn_demo_pause.setEnabled(true);
//停止減少(移除未處理的減少的消息)
handler.removeMessages(WHAT_DECREASE);
//發消息(增加)
handler.sendEmptyMessage(WHAT_INCREASE);
} else if(v==btn_demo_decrease) {//自動減少 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(移除未處理的增加的消息)
handler.removeMessages(WHAT_INCREASE);
//發消息(減少)
handler.sendEmptyMessage(WHAT_DECREASE);
} else if(v==btn_demo_pause) {//暫停
//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/減少(移除未處理的減少/增加的消息)
handler.removeMessages(WHAT_INCREASE);
handler.removeMessages(WHAT_DECREASE);
}
}
}
XML代碼:
<?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="自動增加" />
<Button
android:id="@+id/btn_demo_decrease"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="自動減少" />
<Button
android:id="@+id/btn_demo_pause"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="暫停"
android:enabled="false"/>
</LinearLayout>
Handler原理:
源碼簡單解析:
Message:
屬性:
- public int what;//標識(id)
- public int arg1;//保存int數據
- public int arg2;//保存int數據
- public Object obj;//保存任意數據
- long when;//記錄應該被處理的時間值
- Handler target;//處理message的handler的引用,也就是發消息的handler
- Runnable callback;//用來處理消息的回調器
- Message next;//指向下一個Message,用來形成一個鏈表
- private static Message sPool;//用來緩存處理過的Message對象,以便複用
方法:
- public static Message obtain();//它利用了Message中的消息池(sPool)
Handler:
方法:
- sendMessage(Message msg);//發送即時消息
- sendMessageDelayed(Message msg,long delayMillis);//發送延時消息
- sendEmptyMessage(int what);//發送即時得空消息
- sendEmptyMessageDelayed(int what,long delayMillis);//發送空的延時消息
- sendMessageAtTime(Message msg,long uptimeMillis);//
- removeMessages(int what);//移除還未處理的消息
- handleMessage(Message msg);//處理消息的回調
MessageQueue:
方法:
- enqueueMessage(Message msg,long when);//將Message添加到隊列中,根據when來排序
Looper:
方法:
- loop();//核心方法
final Looper me = myLooper();//得到Looper對象
final MessageQueue queue = me.mQueue;//得到消息對列對象
for(;;){
Message msg = queue.next();//可能處於等待狀態,但是不會阻塞主線程
......
msg.target.dispatchMessage(msg);//調用Handler去分發消息,並處理消息
msg.recycle();//回收message
}