viewpager的setOffscreenPageLimit（）

/**
 * 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();
    }
}

该方法主要设置viewpager的预加载数量，最低不能小于1