ViewPagerCompat.java 文件源码

/**
 * Set a {@link PageTransformer} that will be called for each attached page whenever
 * the scroll position is changed. This allows the application to apply custom property
 * transformations to each page, overriding the default sliding look and feel.
 *
 * <p><em>Note:</em> Prior to Android 3.0 the property animation APIs did not exist.
 * As a result, setting a PageTransformer prior to Android 3.0 (API 11) will have no effect.</p>
 *
 * @param reverseDrawingOrder true if the supplied PageTransformer requires page views
 *                            to be drawn from last to first instead of first to last.
 * @param transformer PageTransformer that will modify each page's animation properties
 */
// Compat Here...
public void setPageTransformer(boolean reverseDrawingOrder, PageTransformer transformer) {
    /*if (Build.VERSION.SDK_INT >= 11) */{
        final boolean hasTransformer = transformer != null;
        final boolean needsPopulate = hasTransformer != (mPageTransformer != null);
        mPageTransformer = transformer;
        setChildrenDrawingOrderEnabledCompat(hasTransformer);
        if (hasTransformer) {
            mDrawingOrder = reverseDrawingOrder ? DRAW_ORDER_REVERSE : DRAW_ORDER_FORWARD;
        } else {
            mDrawingOrder = DRAW_ORDER_DEFAULT;
        }
        if (needsPopulate) populate();
    }
}