使用viewPager滑动控制背景图渐变

改了下引导页 新需求在引导页滑动时滑动上方标题 并且根据滑动渐变背景图片透明度   其实渐变图片和颜色是一样的 说下大概的思路 viewPager控制滑动 把需要滑动得部分放在viewPager中 而渐变背景 直接已RelativeLayout 放在viewPager上面 重点就是背景渐变得控制在viewPager得监听方法里

//当页面在滑动的时候会调用此方法，在滑动被停止之前，此方法回一直被调用。 
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
if (positionOffset == 0 && position > 0) {//避免一页结束时，细微的闪移
return;
}
//arg0 :当前页面，及你点击滑动的页面
// arg1:当前页面偏移的百分比
// arg2:当前页面偏移的像素位置

switch (position) {
case -1:
case 0:
one_to_two.setVisibility(View.VISIBLE);
one_to_two.setAlpha(1f - positionOffset);
two_to_three.setVisibility(View.VISIBLE);
two_to_three.setAlpha(positionOffset);
three_to_one.setVisibility(View.VISIBLE);
three_to_one.setAlpha(0f);
break;
case 1:
one_to_two.setVisibility(View.VISIBLE);
two_to_three.setVisibility(View.VISIBLE);
three_to_one.setVisibility(View.VISIBLE);
if (positionOffset > 0) {
two_to_three.setAlpha(1 - positionOffset);
three_to_one.setAlpha(positionOffset);
one_to_two.setAlpha(0f);
} else {
one_to_two.setAlpha(1 + positionOffset);
two_to_three.setAlpha(0 - positionOffset);
}
break;
case 2:
one_to_two.setVisibility(View.VISIBLE);
two_to_three.setVisibility(View.VISIBLE);
three_to_one.setVisibility(View.VISIBLE);
two_to_three.setAlpha(positionOffset);
one_to_two.setAlpha(0f);
break;

}
}

就行了 简单得一个透明度得设置 不是太复杂