轉載注明出處:http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2014/0814/1650.html
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Android從3.0開始,就添加了很多動畫,ViewPager當然也不例外,相對于非常平庸的預設切換動畫,Google給我們展示了兩個動畫例子:DepthPageTransformer和ZoomOutPageTransformer,實際上我們也可以通過實作ViewPager.PageTransformer來做出完全不同的切換動畫效果。關鍵是要了解transformPage(View view, float position)的參數。view理所當然就是滑動中的那個view,position這裡是float類型,不是平時了解的int位置,而是目前滑動狀态的一個表示,比如當滑動到正全屏時,position是0,而向左滑動,使得右邊剛好有一部被進入螢幕時,position是1,如果前一頁和下一頁基本各在螢幕占一半時,前一頁的position是-0.5,後一頁的posiotn是0.5,是以根據position的值我們就可以自行設定需要的alpha,x/y資訊。
下面,我們來看看Google官方提供的兩種動畫效果的代碼,很簡單,相信每個人看過之後,都能自己實作一種動畫效果,
DepthPageTransformer:
public class DepthPageTransformer implements PageTransformer {
private static float MIN_SCALE = 0.75f;
@SuppressLint("NewApi")
@Override
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 0) { // [-1,0]
// Use the default slide transition when
// moving to the left page
view.setAlpha(1);
view.setTranslationX(0);
view.setScaleX(1);
view.setScaleY(1);
} else if (position <= 1) { // (0,1]
// Fade the page out.
view.setAlpha(1 - position);
// Counteract the default slide transition
view.setTranslationX(pageWidth * -position);
// Scale the page down (between MIN_SCALE and 1)
float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)
* (1 - Math.abs(position));
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
} else { // (1,+Infinity]
// This page is way off-screen to the right.
view.setAlpha(0);
}
}
}
ZoomOutPageTransformer:
public class ZoomOutPageTransformer implements PageTransformer {
private static float MIN_SCALE = 0.85f;
private static float MIN_ALPHA = 0.5f;
@Override
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
int pageHeight = view.getHeight();
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 1) { // [-1,1]
// Modify the default slide transition to
// shrink the page as well
float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
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);
}
// Scale the page down (between MIN_SCALE and 1)
view.setScaleX(scaleFactor);
view.setScaleY(scaleFactor);
// Fade the page relative to its size.
view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
/ (1 - MIN_SCALE) * (1 - MIN_ALPHA));
} else { // (1,+Infinity]
// This page is way off-screen to the right.
view.setAlpha(0);
}
}
}
有了這兩種效果,我們在代碼中設定一下就生效了:mPager.setPageTransformer(true, new DepthPageTransformer());
下面是效果圖:第一張是DepthPageTransformer效果,第二張是ZoomOutPageTransformer效果。
OK,最後奉上源代碼: http://download.csdn.net/detail/weidi1989/6443601