Toast對應的LENGTH_SHORT和LENGTH_LONG分別是多長時間？

我們經常使用Toast，通過LENGTH_SHORT或者LENGTH_LONG，但沒特別注意具體顯示多長時間。今天突然看了一下Toast.java原始碼（android-28），發現程式碼定義如下：

    /**
     * Show the view or text notification for a short period of time.  This time
     * could be user-definable.  This is the default.
     * @see #setDuration
     */
    public static final int LENGTH_SHORT = 0;

    /**
     * Show the view or text notification for a long period of time.  This time
     * could be user-definable.
     * @see #setDuration
     */
    public static final int LENGTH_LONG = 1;
 

大寫懵逼，0和1是什麼鬼？

繼續往下找……

makeText方法沒有什麼實質性呼叫，主要是解析佈局，設定引數，

直接看Toast的show方法，

    /**
     * Show the view for the specified duration.
     */
    public void show() {
        if (mNextView == null) {
            throw new RuntimeException("setView must have been called");
        }

        INotificationManager service = getService();
        String pkg = mContext.getOpPackageName();
        TN tn = mTN;
        tn.mNextView = mNextView;

        try {
            service.enqueueToast(pkg, tn, mDuration);
        } catch (RemoteException e) {
            // Empty
        }
    }
 

繼續跟，這裡通過getService()拿到了NotivicationManagerService的代理INotificationManager，

    static private INotificationManager getService() {
        if (sService != null) {
            return sService;
        }
        sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));
        return sService;
    }
 

然後呼叫了service.enqueueToast(pkg, tn, mDuration);，直接看NotificationManagerService的enqueueToast方法，

@Override
        public void enqueueToast(String pkg, ITransientNotification callback, int duration)
        {
           //...略...
            synchronized (mToastQueue) {
                    //...略...
                    // If it's at index 0, it's the current toast.  It doesn't matter if it's
                    // new or just been updated.  Call back and tell it to show itself.
                    // If the callback fails, this will remove it from the list, so don't
                    // assume that it's valid after this.
                    if (index == 0) {
                        showNextToastLocked();
                    }
	           //...略...
            }
        }

重點關注這個方法showNextToastLocked()，輾轉呼叫到scheduleDurationReachedLocked方法，開始了toast的顯示，繼續跟下去，真是柳暗花明又一村……

前邊是構建ToastRecord，這裡通過Handler進行顯示了

    @GuardedBy("mToastQueue")
    private void scheduleDurationReachedLocked(ToastRecord r)
    {
        mHandler.removeCallbacksAndMessages(r);
        Message m = Message.obtain(mHandler, MESSAGE_DURATION_REACHED, r);
        long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;
        mHandler.sendMessageDelayed(m, delay);
    }

終於發現了最終的duration的真面目。

long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;

在NotificationManagerService.java中定義，

    static final int LONG_DELAY = PhoneWindowManager.TOAST_WINDOW_TIMEOUT;
    static final int SHORT_DELAY = 2000; // 2 seconds

而LONG_DELAY定義在PhoneWindowManager中

    /** Amount of time (in milliseconds) a toast window can be shown. */
    public static final int TOAST_WINDOW_TIMEOUT = 3500; // 3.5 seconds

結果，不言而喻。