三分鐘帶你領略HandlerThread？

1、基礎使用

public class DemoActivity extends AppCompatActivity {

    private static final String TAG = "DemoActivity";

    private WorkHandler workHandler;

    private Button sendMsgDiffBt;

    @Override
    protected void onCreate(@Nullable @org.jetbrains.annotations.Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_demo);
        HandlerThread workThread = new HandlerThread("SessionManager$1");
        workThread.start();
        workHandler = new WorkHandler(workThread.getLooper(),this);
        sendMsgDiffBt = findViewById(R.id.bt_send_msg_diff);
        sendMsgDiffBt.setOnClickListener(view -> {
            workHandler.sendEmptyMessage(1);
        });
    }

    static class WorkHandler extends Handler {
        
        private WeakReference<AppCompatActivity> activityWeakReference = null;

        public WorkHandler(Looper looper, AppCompatActivity appCompatActivity) {
            super(looper);
            activityWeakReference = new WeakReference<>(appCompatActivity);
        }

        @Override
        public void handleMessage(Message msg) {
            int what = msg.what;
            Log.i(TAG, "handleMessage: " + Looper.getMainLooper().getThread().getName());
            Log.i(TAG, "handleMessage: " + Looper.myLooper().getThread().getName());
            Log.i(TAG, "thread:" + Thread.currentThread().getId() + "," + Thread.currentThread().getName());
        }
    }
}

以上是一個Demo標準的寫法，沒有業務邏輯，我們來看一一下他的輸出

根據控制臺的輸出handleMessage的訊息我們可以看出來，，主執行緒是main執行緒，而當前執行緒是我們自定義名字的執行緒，所以我們可以去猜測他就是一個執行緒，由于沒有證據去支持這個猜測，我們需要去看原始碼，去證實這個猜測；

2、原始碼決議

原始碼不多我們就將他的所有都展示出來，注釋我就轉換成中文了，方便我們我們去決議它了

package android.os;

import android.annotation.NonNull;
import android.annotation.Nullable;
public class HandlerThread extends Thread {
    int mPriority;
    int mTid = -1;
    Looper mLooper;
    private @Nullable
    Handler mHandler;

    public HandlerThread(String name) {
        super(name);
        mPriority = Process.THREAD_PRIORITY_DEFAULT;
    }

    /**
     * Constructs a HandlerThread.
     * @param name 名稱
     * @param priority 優先級 越大優先級越高
     * {@link android.os.Process} and not from java.lang.Thread.
     */
    public HandlerThread(String name, int priority) {
        super(name);
        mPriority = priority;
    }

    /**
     * 可以用來處理主執行緒的業務
     */
    protected void onLooperPrepared() {
    }

    @Override
    public void run() {
        mTid = Process.myTid();
        Looper.prepare();
        synchronized (this) {
            mLooper = Looper.myLooper();
            notifyAll();
        }
        Process.setThreadPriority(mPriority);
        onLooperPrepared();
        Looper.loop();
        mTid = -1;
    }

    /**
     * This method returns the Looper associated with this thread. If this thread not been started
     * or for any reason isAlive() returns false, this method will return null. If this thread
     * has been started, this method will block until the looper has been initialized.
     * @return The looper.
     */
    public Looper getLooper() {
        if (!isAlive()) {
            return null;
        }

        // If the thread has been started, wait until the looper has been created.
        synchronized (this) {
            while (isAlive() && mLooper == null) {
                try {
                    wait();
                } catch (InterruptedException e) {
                }
            }
        }
        return mLooper;
    }

    /**
     * @return  獲取當前Handler
     * @hide
     */
    @NonNull
    public Handler getThreadHandler() {
        if (mHandler == null) {
            mHandler = new Handler(getLooper());
        }
        return mHandler;
    }

    /**
     * 非安全的退出處理程式執行緒的回圈器 
     * @see #quitSafely
     */
    public boolean quit() {
        Looper looper = getLooper();
        if (looper != null) {
            looper.quit();
            return true;
        }
        return false;
    }

    /**
     * 安全的退出處理程式執行緒的回圈器
     * @see #quitSafely
     */
    public boolean quitSafely() {
        Looper looper = getLooper();
        if (looper != null) {
            looper.quitSafely();
            return true;
        }
        return false;
    }

    /**
     * Returns the identifier of this thread. See Process.myTid().
     */
    public int getThreadId() {
        return mTid;
    }
}

總結一下：從原始碼當中我們首先可以看出來在android包下，他是系統提供，其次可看到HandlerThread 繼承的就是一個Thread ，通過對Looper的操作進行分裝的一個幫助類，如果對Looper不熟悉的，可以去了解一下Handler的訊息機制，這個就不多說這個了，了解其原理那我們是不是也可以封裝一個我們自己的HandlerThread，哈哈，那根據它的業務邏輯我們是不是可以應用到我們的應用場景了，比如單執行緒任務當中，這個看業務需求，不是必須的拉，