Android ViewPager 动画淡入/淡出而不是幻灯片

ViewPager animation fade in/out instead of slide

提问by KKO

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.

我从这里得到了 FragmentBasics 示例。有没有办法让 ViewPager 动画在我滑动而不是左右滑动时简单地淡入淡出？我一直在用 PageTransformer 尝试一些东西，但没有成功，我仍然可以看到它在滑动。所以我想我需要以某种方式强制它的位置保持原状，而滑动我的手指只会影响 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);
            }
        }
    }

回答by murena

This should work better for the fade in/out transform:

这对于淡入/淡出变换应该更有效：

        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by umberto_sidoti

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.

根据@murena 的回答，这对于淡入/淡出变换应该更有效。在动画结束时，位置恢复为默认值。

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));
            }
        }

回答by stephan

A simple fading transformer could be implemented like this:

一个简单的衰落变换器可以这样实现：

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);
        }
    }
}

Maybe not exactly what your looking for, but a good starting point.

也许不完全是你想要的，但一个很好的起点。

回答by Jo?o Dinis

Fade according to Google: https://developer.android.com/training/animation/reveal-or-hide-view

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));
            }
        });
    }

回答by Pablo S. Campos

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:

我发现@murena 的回答非常有帮助。但是，当我尝试向每个选项卡添加 OnClickListener 时遇到了问题。我需要每个页面打开一个不同的 URL 链接。我修改了代码以隐藏视线之外的视图，并添加了一些额外的效果以 0.5 的速度滑动视图：

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);
    }
}