一丶概述

本週的學習計劃是Android通訊模組，內容：單執行緒，多執行緒通訊方式，Handler 與UI Thread的互動，Handler接合子執行緒的使用。

二丶效果演示（原始碼連結見文末）

三丶實現功能

1.演示使用Handler常見崩潰

2.handler更新TextView的UI

3.實現圖片輪播及停止

4.輸出handleMessage(Message mes)的mes列印

5.自定義執行緒相關handler測試執行

6.Handler非同步訊息處理測試

handler相關方法運用

四丶正文

1.選說說多執行緒（工作到現在用的不太多，都是別人封裝好的框架直接用）

2.Handler

最初學習Handler是通過扣丁學堂，之前的文章：扣丁學堂——Handler

最近開發用到的SwipeRefreshLayout 的onRefresh()方法，也常看到handler

@Override
public void onRefresh() {
    new Handler().postDelayed(new Runnable() {
        @Override
public void run() {
            mEntities.clear();
intData();
//★3.通知recycleView改變了資料
homeAdapter.notifyDataSetChanged();
 
//★4.記得關閉重新整理，否則重新整理球一直在轉
mSwipeRefreshLayout.setRefreshing(false);
}
    }, 50);
}

好了，現在重新認識

2.Handler類的引入:

3.Handler的執行流程圖：

流程圖解析: 
相關名詞

• UI執行緒:就是我們的主執行緒,系統在建立UI執行緒的時候會初始化一個Looper物件,同時也會建立一個與其關聯的MessageQueue;
• Handler:作用就是傳送與處理資訊,如果希望Handler正常工作,在當前執行緒中要有一個Looper物件
• Message
  :Handler接收與處理的訊息物件
• MessageQueue:訊息佇列,先進先出管理Message,在初始化Looper物件時會建立一個與之關聯的MessageQueue;
• Looper:每個執行緒只能夠有一個Looper,管理MessageQueue,不斷地從中取出Message分發給對應的Handler處理！

簡單點說：

當我們的子執行緒想修改Activity中的UI元件時,我們可以新建一個Handler物件,通過這個物件向主執行緒傳送資訊;而我們傳送的資訊會先到主執行緒的MessageQueue進行等待,由Looper按先入先出順序取出,再根據message物件的what屬性分發給對應的Handler進行處理！

4.Handler的相關方法:

• void handleMessage(Message msg):處理訊息的方法,通常是用於被重寫!
• sendEmptyMessage(int what):傳送空訊息
• sendEmptyMessageDelayed(int what,long delayMillis):指定延時多少毫秒後傳送空資訊
• sendMessage(Message msg):立即傳送資訊
• sendMessageDelayed(Message msg):指定延時多少毫秒後傳送資訊
• final boolean hasMessage(int what):檢查訊息佇列中是否包含what屬性為指定值的訊息 
  如果是引數為(int what,Object object):除了判斷what屬性,還需要判斷Object屬性是否為指定物件的訊息

5.看程式碼

case R.id.id_btn1:
    new Thread() {
        @Override
public void run() {
            try {
                Thread.sleep(1000 * 3);
idTv.setText("蹦啦");
} catch (InterruptedException e) {
                e.printStackTrace();
}
        }
    }.start();
    break;
case R.id.id_btn2:
    new Thread() {
        @Override
public void run() {
            try {
                Thread.sleep(1000 * 3);
handler.post(new Runnable() {
                    @Override
public void run() {
                        idTv.setText("又長帥了");
}
                });
} catch (InterruptedException e) {
                e.printStackTrace();
}
        }
    }.start();
    break;

關於這裡有個小插曲，涉及原始碼解讀，觀看愛哥部落格

2.迴圈播放圖片及停止

Handler handler = new Handler();
Thread myThread = new Thread(){
    @Override
public void run() {
        index++;
index = index%3;
System.out.println(index);
idImg.setImageResource(images[index]);
handler.postDelayed(myThread,1000);
}
};

case R.id.id_btn3:
    handler.postDelayed(myThread,1000);
    break;
case R.id.id_btn4:
    handler.removeCallbacks(myThread);

handler.postDelayed(X,X)是延遲執行執行緒

handler.removeCallbacks(X)移除執行緒中所有訊息和回撥

3.handle傳遞message可攜帶的內容有（int 實體內等）

Handler customHander = new Handler() {
    @Override
public void handleMessage(Message msg) {
        idTv.setText("msg.arg1>"+msg.arg1+ "\nmsg.arg2>" +msg.arg2 +"\nmsg.obj>"+((Person)msg.obj).toString());
}
};

            case R.id.id_btn5:
                Person dog=new Person("金三胖",1);
//                Message message = new Message();
Message message= customHander.obtainMessage();
message.arg1 = 1;
message.arg2 = 2;
message.obj = dog;
//                customHander.sendMessage(message);
message.sendToTarget();
                break;

4.訊息攔截測試

Handler interceptHander = new Handler(new Handler.Callback() {
    @Override
public boolean handleMessage(Message msg) {
        Toast.makeText(HandlerDemoActivity.this, "callback handleMessage", Toast.LENGTH_SHORT).show();
System.out.println("is intercept Handler>"+msg.what);
// 設定true攔截訊息
return true;
}
}){
    @Override
public void handleMessage(Message msg) {
        System.out.println("is intercept Handler");
}
};

case R.id.id_btn6:
    interceptHander.sendEmptyMessage(1);
    break;

  case R.id.id_btn7:
                new Thread() {
                    @Override
public void run() {
                        try {
                            Thread.sleep(1000*3);
//                    idTv.setText("UI執行緒更新UI會出現什麼異常呢？");
new Handler().post(new Runnable() {
                                @Override
public void run() {
                                    idTv.setText("又蹦啦");
}
                            });
} catch (InterruptedException e) {
                            e.printStackTrace();
}
                    }
                }.start();
                break;

public class HandlerActivity extends AppCompatActivity {
    private MyThread myThread;
    private Handler handler = new Handler(){
        @Override
public void handleMessage(Message msg) {
            System.out.println("UI ==:"+ Thread.currentThread());
}
    };
    class MyThread extends Thread {
        public Handler handler;
@Override
public void run() {
            Looper.prepare();
handler= new Handler(){
                @Override
public void handleMessage(Message msg) {
                    System.out.println("currentThread:=="+ Thread.currentThread());
}
            };
Looper.loop();
}
    }

    @Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
setContentView(R.layout.activity_handler);
myThread = new MyThread();
myThread.start();
        try {
            Thread.sleep(1000*5);
} catch (InterruptedException e) {
            e.printStackTrace();
}
        myThread.handler.sendEmptyMessage(1);
handler.sendEmptyMessage(1);
}
}

06-29 17:07:30.519 9652-11848/com.example.jinboy.codertodeveloperbytcler I/System.out: currentThread:==Thread[Thread-9681,5,main]
06-29 17:07:30.659 9652-9652/com.example.jinboy.codertodeveloperbytcler I/System.out: UI ==:Thread[main,5,main]

7.Handler非同步訊息處理

public class HandlerThreadActivity extends AppCompatActivity implements View.OnClickListener {
    private Button idBtn1,idBtn2;
    private Handler threadhandler;
    private HandlerThread thread;
Handler handler = new Handler() {
        @Override
public void handleMessage(Message msg) {
            System.out.println("UI thread==>" + Thread.currentThread());
// 給主執行緒傳送訊息
Message message = new Message();
message.what =1;
threadhandler.sendMessageDelayed(message, 1000);
}
    };
@Override
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
setContentView(R.layout.activity_handler_thread);
idBtn1 = (Button) findViewById(R.id.id_btn1);
idBtn2 = (Button) findViewById(R.id.id_btn2);
idBtn1.setOnClickListener(this);
idBtn2.setOnClickListener(this);
thread = new HandlerThread("Handler Thread");
thread.start();
threadhandler = new Handler(thread.getLooper()) {
            @Override
public void handleMessage(Message msg) {
                // 處理耗時操作
System.out.println("current thread==>" + Thread.currentThread());
// 給主執行緒傳送訊息
Message message = new Message();
message.what =1;
handler.sendMessageDelayed(message, 1000);
}
        };
//        threadhandler.sendEmptyMessage(1);
}

    @Override
public void onClick(View view) {
        switch (view.getId()) {
            case R.id.id_btn1:
                handler.sendEmptyMessage(1);
                break;
            case R.id.id_btn2:
                handler.removeMessages(1);
threadhandler.removeMessages(1);
                break;
}
    }
}

五丶參考連結和拓展學習

參考內容：

拓展學習：

六丶日常開發案例

1.Android避免在主執行緒進行網路請求和UI操作

方法一：執行緒請求網路+Handler更新UI

//handler 處理返回的請求結果
handler = new Handler() {
    @Override
public void handleMessage(Message msg) {
        super.handleMessage(msg);
Bundle data = msg.getData();
String val = data.getString("value");
tv_name.setText(tvName);
tv_originalArticleNumber.setText(tvOriginalArticleNumber);
tv_visitNumber.setText(tvVisitNumber);
tv_mark.setText(tvMark);
tv_rank.setText(tvRank);
Log.i("mylog", "請求結果-->" + val);
}
};
//新執行緒進行網路請求
Runnable runnable = new Runnable() {
    @Override
public void run() {
        BlogAuthor blogAuthor = JsoupUtil.getBlogAutoMessage();
tvName = blogAuthor.getAuthorName() + "\n" + blogAuthor.getCode()
                + "\n" + blogAuthor.getMyHelloWorld();
tvOriginalArticleNumber = blogAuthor.getOriginalArticleNumber();
tvVisitNumber = blogAuthor.getVisitNumber();
tvMark = blogAuthor.getMark();
tvRank = blogAuthor.getRank();
Message msg = new Message();
Bundle data = new Bundle();
data.putString("value", "請求結果");
msg.setData(data);
handler.sendMessage(msg);
}
};
new Thread(runnable).start();  //啟動子執行緒

setContentView(R.layout.activity_main);
if (android.os.Build.VERSION.SDK_INT > 9) {
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
}