View translation in sliding a ViewPager

Question

I was reading an example on customizing ViewPager\'s sliding page animation that entails translating the page(View) to a certain amount. The example is

Answer 1

There is one thing you are missing here, the PageTransformer is applied to the views AFTER they have been positioned.

So, with or without a PageTransformer attached to the PageView - when you scroll between pages - you simply doing a scroll (like in a LiseView) with SNAP capabilities.

The PageTransformer only adds effects on top of that.

So the purpose of,

float vertMargin = pageHeight * (1 - scaleFactor) / 2;
float horzMargin = pageWidth * (1 - scaleFactor) / 2;
if (position < 0) {
    view.setTranslationX(horzMargin - vertMargin / 2);
} else {
    view.setTranslationX(-horzMargin + vertMargin / 2);
}

is NOT to move the pages - but to compensate the page shrinking.

Without it, the page will have some ugly side effects. TRY IT, remove the lines :) - The views will go right/left but the positioning will be off.

So, the translation X does not move the page, but, in this case, simply manages the pages spacing to improve the animation feel - the above is the Math for it. What it does is to reduce the space between the pages based on the screen height/width. First it negates the space (horzMargin) then it adds a little spacing (- vertMargin / 2)

And that is why your calculation is not good (w*x) - You are trying to move the page - But it is already moving.