[Android]ViewPager如何只初始化一個頁面

使用過ViewPager的應該都知道，ViewPager的setoffscreenpagelimit()方法，使用該方法可以設置在ViewPager滑動時，左右兩側各保存多少個頁面，那我們直接設置setoffscreenpagelimit(0)，不就好了嗎。當然不是這樣子的，當我們setoffscreenpagelimit(0)時，如果細心的話，就會發現，並不是只保存當前頁面，而是兩邊的頁面同時也有保存。這時候，我們懷着疑問去閱讀源碼，才會發現，這個方法竟然是這樣寫的：

/**
     * Set the number of pages that should be retained to either side of the
     * current page in the view hierarchy in an idle state. Pages beyond this
     * limit will be recreated from the adapter when needed.
     *
     * <p>This is offered as an optimization. If you know in advance the number
     * of pages you will need to support or have lazy-loading mechanisms in place
     * on your pages, tweaking this setting can have benefits in perceived smoothness
     * of paging animations and interaction. If you have a small number of pages (3-4)
     * that you can keep active all at once, less time will be spent in layout for
     * newly created view subtrees as the user pages back and forth.</p>
     *
     * <p>You should keep this limit low, especially if your pages have complex layouts.
     * This setting defaults to 1.</p>
     *
     * @param limit How many pages will be kept offscreen in an idle state.
     */
    public void setOffscreenPageLimit(int limit) {
        if (limit < DEFAULT_OFFSCREEN_PAGES) {
            Log.w(TAG, "Requested offscreen page limit " + limit + " too small; defaulting to "
                    + DEFAULT_OFFSCREEN_PAGES);
            limit = DEFAULT_OFFSCREEN_PAGES;
        }
        if (limit != mOffscreenPageLimit) {
            mOffscreenPageLimit = limit;
            populate();
        }
    }

這個方法的默認值竟然是1。
這樣子，當我們只想初始化一個頁面的時候，就要注意了。這個時候，我采用的是懶加載的方式，因為在頁面進入前台的時候，是會調用setUserVisibleHint()這個方法的，通過這個方法我們可以獲得當前當前頁面是否對用戶可見，並在對用戶可見的時候進行初始化，這時還要注意一點，那就是setUserVisibleHint()這個方法的調用並不保證View等需要的東西是否已經初始化成功，所以我們還是要判斷一下的。