這個雖然簡單但還是簡單的記錄一下：

有三個tablayout，這是每個log日誌列印的結果

自己試驗過的都能明白這三個狀態是什麼意思，貼上原始碼的解釋：

 /**
     * Callback interface invoked when a tab's selection state changes.
     */
    public interface OnTabSelectedListener {

        /**
         * Called when a tab enters the selected state.當選項卡進入選定狀態時呼叫。
         *
         * @param tab The tab that was selected選中的選項卡
         */
        public void onTabSelected(Tab tab);

        /**
         * Called when a tab exits the selected state.當選項卡退出所選狀態時呼叫
         *
         * @param tab The tab that was unselected選項卡未選中的選項卡
         */
        public void onTabUnselected(Tab tab);

        /**
         * Called when a tab that is already selected is chosen again by the user. Some applications當用戶再次選擇已選中的選項卡時呼叫。一些應用程式可以使用此操作返回到類別的頂層。
         * may use this action to return to the top level of a category.
         *
         * @param tab The tab that was reselected.重新選擇的選項卡。
         */
        public void onTabReselected(Tab tab);
    }