[Android]ViewPager如何只初始化一个页面

使用过ViewPager的应该都知道，ViewPager的setoffscreenpagelimit()方法，使用该方法可以设置在ViewPager滑动时，左右两侧各保存多少个页面，那我们直接设置setoffscreenpagelimit(0)，不就好了吗。当然不是这样子的，当我们setoffscreenpagelimit(0)时，如果细心的话，就会发现，并不是只保存当前页面，而是两边的页面同时也有保存。这时候，我们怀着疑问去阅读源码，才会发现，这个方法竟然是这样写的：

/**
     * 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();
        }
    }

这个方法的默认值竟然是1。

这样子，当我们只想初始化一个页面的时候，就要注意了。这个时候，我采用的是懒加载的方式，因为在页面进入前台的时候，是会调用setUserVisibleHint()这个方法的，通过这个方法我们可以获得当前当前页面是否对用户可见，并在对用户可见的时候进行初始化，这时还要注意一点，那就是setUserVisibleHint()这个方法的调用并不保证View等需要的东西是否已经初始化成功，所以我们还是要判断一下的。