Toast对应的LENGTH_SHORT和LENGTH_LONG分别是多长时间？

我们经常使用Toast，通过LENGTH_SHORT或者LENGTH_LONG，但没特别注意具体显示多长时间。今天突然看了一下Toast.java源码（android-28），发现代码定义如下：

    /**
     * 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;

大写懵逼，0和1是什么鬼？

继续往下找……

makeText方法没有什么实质性调用，主要是解析布局，设置参数，

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
        }
    }

继续跟，这里通过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;
    }

然后调用了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...
            }
        }

重点关注这个方法showNextToastLocked()，辗转调用到scheduleDurationReachedLocked方法，开始了toast的显示，继续跟下去，真是柳暗花明又一村……

前边是构建ToastRecord，这里通过Handler进行显示了

    @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);
    }

终于发现了最终的duration的真面目。

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

在NotificationManagerService.java中定义，

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

而LONG_DELAY定义在PhoneWindowManager中

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

结果，不言而喻。