原理

PreferenceActivity类中有一个静态变量 EXTRA_SHOW_FRAGMENT

    /**
     * When starting this activity, the invoking Intent can contain this extra
     * string to specify which fragment should be initially displayed.
     * <p/>Starting from Key Lime Pie, when this argument is passed in, the PreferenceActivity
     * will call isValidFragment() to confirm that the fragment class name is valid for this
     * activity.
     */
大意：开启acitivity活动时，可以通过intent包含额外的数据（类型：EXTRA_SHOW_FRAGMENT）来指定最开始展示的fragment
    public static final String EXTRA_SHOW_FRAGMENT = ":android:show_fragment";