Android 訊息處理源碼分析（2）

標籤：android源碼分析

 Android 訊息處理源碼分析（1）點擊開啟連結

繼續接著分析剩下的類檔案

Looper.javapublic final class Looper {    final MessageQueue mQueue;   //訊息佇列    final Thread mThread;   //Looper聯絡的線程        public static void prepare() {        prepare(true);    }        private static void prepare(boolean quitAllowed) {   //先會檢查是否有Looper，若有則拋出異常，沒有的話則建立一個Looper執行個體儲存起來        if (sThreadLocal.get() != null) {            throw new RuntimeException("Only one Looper may be created per thread");        }        sThreadLocal.set(new Looper(quitAllowed));    }    public static void prepareMainLooper() {        prepare(false);        synchronized (Looper.class) {            if (sMainLooper != null) {                throw new IllegalStateException("The main Looper has already been prepared.");            }            sMainLooper = myLooper();        }    }   //在這個線程中運行訊息佇列，調用quit（）停止   public static void loop() {...final MessageQueue queue = me.mQueue;        // Make sure the identity of this thread is that of the local process,        // and keep track of what that identity token actually is.        Binder.clearCallingIdentity();        final long ident = Binder.clearCallingIdentity();        for (;;) {            Message msg = queue.next(); // 從訊息佇列中取出一條訊息            if (msg == null) {                // No message indicates that the message queue is quitting.                return;            }            // This must be in a local variable, in case a UI event sets the logger            Printer logging = me.mLogging;            if (logging != null) {                logging.println(">>>>> Dispatching to " + msg.target + " " +                        msg.callback + ": " + msg.what);            }            msg.target.dispatchMessage(msg);   //交給msg的handler分發訊息處理...   }    //取出當前線程的Looper，返回空則表示當前線程沒有Looper    public static Looper myLooper() {        return sThreadLocal.get();    }}

Handler.javapublic class Handler {     //定義Callback介面     public interface Callback {      public boolean handleMessage(Message msg);     }     //子類要實現的訊息處理方法     public void handleMessage(Message msg) {     }     * Handle system messages here.     */    public void dispatchMessage(Message msg) {        //分發資訊        if (msg.callback != null) {          //若指定了msg.callback，則由它處理            handleCallback(msg);        } else {            if (mCallback != null) {        //若指定了Handler.mCallback，則由它處理                if (mCallback.handleMessage(msg)) {    //調用mCallback介面的實現方法                    return;                }            }            handleMessage(msg);   最後才調用Handler自身重載的handleMessage方法        }    }    分發訊息函數中，訊息先會檢查自身有沒有處理自身的回調Runnable，若有則由它處理，若沒有則會檢查該handler有無自身的回調處理，若有則調用，若沒有則調用自身重載的handleMessage方法    //Handler的產生總是和它當前所處線程有關的，如果當前線程中沒有一個Looper，則會報錯，UI線程中預設有產生Looper的函數    public Handler() {        this(null, false);    }        //使用指定的Looper（可以處理那個Looper線程中的訊息），不用預設的從當前線程中取出Looper    public Handler(Looper looper) {        this(looper, null, false);    }   ...}

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Android 訊息處理源碼分析（2）