问题
I got the FragmentBasics example from here. Is there a way make the ViewPager animation simply fade in and out when I swipe instead of sliding left and right? I've been trying some stuff with PageTransformer, but no success, I can still see it sliding. So I guess I need to somehow force its position to stay put, while sliding my finger only affects the alpha.
public class SecondActivity extends Activity {
SectionsPagerAdapter mSectionsPagerAdapter;
ViewPager mViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
// Create the adapter that will return a fragment for each of the three
// primary sections of the activity.
mSectionsPagerAdapter = new SectionsPagerAdapter(getFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setPageTransformer(false, new FadePageTransformer());
mViewPager.setAdapter(mSectionsPagerAdapter);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.second, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
return PlaceholderFragment.newInstance(position + 1);
}
@Override
public int getCount() {
// Show 3 total pages.
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.title_section1).toUpperCase(l);
case 1:
return getString(R.string.title_section2).toUpperCase(l);
case 2:
return getString(R.string.title_section3).toUpperCase(l);
}
return null;
}
}
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_second, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.section_label);
textView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
return rootView;
}
}
public class FadePageTransformer implements ViewPager.PageTransformer {
public void transformPage(View view, float position) {
if (position < -1 || position > 1) {
view.setAlpha(0);
}
else if (position <= 0 || position <= 1) {
// Calculate alpha. Position is decimal in [-1,0] or [0,1]
float alpha = (position <= 0) ? position + 1 : 1 - position;
view.setAlpha(alpha);
}
else if (position == 0) {
view.setAlpha(1);
}
}
}
回答1:
This should work better for the fade in/out transform:
public void transformPage(View view, float position) {
view.setTranslationX(view.getWidth() * -position);
if(position <= -1.0F || position >= 1.0F) {
view.setAlpha(0.0F);
} else if( position == 0.0F ) {
view.setAlpha(1.0F);
} else {
// position is between -1.0F & 0.0F OR 0.0F & 1.0F
view.setAlpha(1.0F - Math.abs(position));
}
}
回答2:
Based on a @murena's answer, this should work better for the fade in/out transform. At the end of animation the position is restored to default value.
public void transformPage(View view, float position) {
if(position <= -1.0F || position >= 1.0F) {
view.setTranslationX(view.getWidth() * position);
view.setAlpha(0.0F);
} else if( position == 0.0F ) {
view.setTranslationX(view.getWidth() * position);
view.setAlpha(1.0F);
} else {
// position is between -1.0F & 0.0F OR 0.0F & 1.0F
view.setTranslationX(view.getWidth() * -position);
view.setAlpha(1.0F - Math.abs(position));
}
}
回答3:
A simple fading transformer could be implemented like this:
private static class FadePageTransformer implements ViewPager.PageTransformer {
public void transformPage(View view, float position) {
view.setAlpha(1 - Math.abs(position));
if (position < 0) {
view.setScrollX((int)((float)(view.getWidth()) * position));
} else if (position > 0) {
view.setScrollX(-(int) ((float) (view.getWidth()) * -position));
} else {
view.setScrollX(0);
}
}
}
Maybe not exactly what your looking for, but a good starting point.
回答4:
I found @murena's answer super helpful. However, I ran into a problem when I tried to add an OnClickListener to each tab. I needed each page to open a different URL link. I modified the code to hide the views that are out of sight and added a little extra effect to slide the view at .5 the speed:
public void transformPage(View view, float position) {
if (position <= -1.0F || position >= 1.0F) { // [-Infinity,-1) OR (1,+Infinity]
view.setAlpha(0.0F);
view.setVisibility(View.GONE);
} else if( position == 0.0F ) { // [0]
view.setAlpha(1.0F);
view.setVisibility(View.VISIBLE);
} else {
// Position is between [-1,1]
view.setAlpha(1.0F - Math.abs(position));
view.setTranslationX(-position * (view.getWidth() / 2));
view.setVisibility(View.VISIBLE);
}
}
回答5:
Fade according to Google: https://developer.android.com/training/animation/reveal-or-hide-view
viewPager.setPageTransformer(false, new ViewPager.PageTransformer() {
@Override
public void transformPage(@NonNull View page, float position) {
page.setAlpha(0f);
page.setVisibility(View.VISIBLE);
// Start Animation for a short period of time
page.animate()
.alpha(1f)
.setDuration(page.getResources().getInteger(android.R.integer.config_shortAnimTime));
}
});
}
来源：https://stackoverflow.com/questions/25096069/viewpager-animation-fade-in-out-instead-of-slide