ViewPager动画淡入/淡出而不是幻灯片

Question

我从这里得到了FragmentBasics示例.当我滑动而不是左右滑动时,有没有办法让ViewPager动画简单地淡入淡出？我一直在尝试使用PageTransformer的一些东西,但没有成功,我仍然可以看到它滑动.所以我想我需要以某种方式强迫它的位置保持不变,而滑动我的手指只影响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);
            }
        }
    }

Answer 1

这对于淡入/淡出变换应该更好:

        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));
            }
        }

Answer 2

基于@ murena的答案,这对于淡入/淡出变换应该更好.在动画结束时,位置将恢复为默认值.

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));
            }
        }

Answer 3

根据谷歌淡出：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));
    }
});

Answer 4

一个简单的衰落变压器可以像这样实现:

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);
        }
    }
}

也许不完全是你想要的,但一个很好的起点.