我从这里获得了 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和淡出？我一直在尝试使用 PageTransformer 进行一些操作，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不变，而滑动我的手指只会影响阿尔法。
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);
}
}
}
这应该更适合淡入/淡出变换：
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));
}
}
根据 @murena 的回答，这对于淡入/淡出变换应该效果更好。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));
}
}
根据谷歌的说法淡入淡出： 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));
}
});
一个简单的衰落变压器可以这样实现：
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);
}
}
}
也许不完全是您想要的，但这是一个很好的起点。
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不同的 URL 链接。我修改了代码以隐藏看不见的视图，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);
}
}
就我而言，我使用的是 @umberto_sidoti 解决方案，但我面临着 alpha 与页面切换不一致的问题，有时寻呼机会显示空白页面（当将 alpha 设置为 0F 时）更长的时间。这是因为从当前页面到目标页面的每个页面都会多次调用 TransformPage 函数。我通过添加额外的检查来区分 tranformPage 中的目标页面解决了这个问题。
override fun transformPage(page: View, position: Float) {
if(position <= -1.0F || position >= 1.0F) {
page.translationX = page.width * position;
} else if( position == 0.0F ) {
page.translationX = page.width * position;
} else {
// position is between -1.0F & 0.0F OR 0.0F & 1.0F
page.translationX = page.width * -position;
}
if(position!=0.0f) return
page.setAlpha(0.25f)
page.visibility = View.VISIBLE
// Start Animation for a short period of time
page.animate()
.alpha(1f)
.setDuration(800);
}