好的,所以我正在尝试实现一个包含三个页面的ViewPager,并在每个页面上都有独特的内容,所以我建立了一个系统,我根据页面索引来扩展不同的布局。这一切在我导航时起作用,但我注意到Fragment被调用了两次。
这是我的FragmentAcivity类:
public class TutorialScreen extends FragmentActivity {
private static final String TAG = "TAG";
private static final int NUM_PAGES = 3;
private ViewPager pager; // animation handler
private PagerAdapter adapter; // provides pages to pager
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.tutorial_layout);
// Instantiate Pager & Adapter
pager = (ViewPager) findViewById(R.id.pager);
adapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
pager.setAdapter(adapter);
Log.v(TAG, "Initial Page is " + pager.getCurrentItem()); // this logs '0' - which is what i want
pager.setCurrentItem(pager.getCurrentItem());
}
@Override
public void onBackPressed() {
if(pager.getCurrentItem() == 0) {
super.onBackPressed();
}
else {
pager.setCurrentItem(pager.getCurrentItem() -1);
}
}
// Pager Adapter SubClass
private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
public ScreenSlidePagerAdapter(FragmentManager fm) {
super(fm);
Log.v(TAG, "constructor"); // this logs once
pager.setCurrentItem(pager.getCurrentItem());
}
@Override
public Fragment getItem(int position) {
Log.v(TAG, "getItem " + position); // this logs twice
return new ScreenSlidePageFragment(position); // note I've overridden the constructor
}
@Override
public int getCount() {
return NUM_PAGES;
}
}
}
和我的片段类:
public class ScreenSlidePageFragment extends Fragment {
private static int pageIndex;
private static final String TAG = "TAG";
ScreenSlidePageFragment(int id) {
pageIndex = id;
Log.v(TAG, "Page Index is " + pageIndex); // this logs twice
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
int resID = -1;
switch(pageIndex) {
case 0:
resID = R.layout.tutorial_page1;
break;
case 1:
resID = R.layout.tutorial_page2;
break;
case 2:
resID = R.layout.tutorial_page3;
break;
default:
resID = R.layout.tutorial_page1;
break;
}
Log.v(TAG, "Res Index is " + resID); // this logs twice
ViewGroup rootView = (ViewGroup) inflater.inflate(resID, container, false);
return rootView;
}
}
日志
构造 getItem 0 页面索引为0 getItem 1 页面索引是1 Res Index是2130903043 Res Index是2130903043
所以基本上它会立即跳到第二页,无论我是否用setCurrentItem()设置位置......
我认为我可能会因为尝试只有一个Fragment类而不是每个匹配布局的单独一个而作弊,但是......这应该有用吗?
请注意,我看到一个(我认为)相关的问题,第二个(初始)页面出现两次 - 一次最初,然后再次刷到下一页(应该是第3页?)。一旦我导航到第3页(经过两次滑动)后,我可以一直回到第1页(应该是初始页面)。
思考?我做错了什么?
答案 0 :(得分:3)
所以,我解决了我自己的(根)问题(虽然不是我遇到的奇怪的索引案例)。
我对ViewPager中每个页面的单个内容实例化的误解是,会反复使用一个Fragment,我会将参数传递给它的构造函数,以便告诉它哪个布局为膨胀。
相反,我意识到我应该拥有完全独立的Fragment类,每个类都拥有它自己独特的布局,我可以使用FragmentStatePagerAdapter中getItem()的相同位置id来实例化正确的Fragment ......现在对我有意义。
见下面的代码:
public class TutorialScreen extends FragmentActivity {
private static final int NUM_PAGES = 3;
private ViewPager pager;
private PagerAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.tutorial_layout);
// Instantiate Pager & Adapter
pager = (ViewPager) findViewById(R.id.pager);
adapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
pager.setAdapter(adapter);
}
@Override
public void onBackPressed() {
if(pager.getCurrentItem() == 0) {
super.onBackPressed();
}
else {
pager.setCurrentItem(pager.getCurrentItem() -1);
}
}
// PagerAdapter SubClass
private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
public ScreenSlidePagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
Fragment fragment;
switch(position) {
case 0:
fragment = new TutorialPage1();
break;
case 1:
fragment = new TutorialPage2();
break;
case 2:
fragment = new TutorialPage3();
break;
default:
fragment = new TutorialPage1();
break;
}
return fragment;
}
@Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
@Override
public int getCount() {
return NUM_PAGES;
}
} /* EOC */
} /* EOC */
答案 1 :(得分:0)
所以,我正在使用相同的片段。 适配器:
public class IncomeWeekFragmentAdapter extends FragmentStatePagerAdapter {
List<String> titlesList;
List<String> reqDates;
public IncomeWeekFragmentAdapter(FragmentManager fm, List<String> titles, List<String> reqDates) {
super(fm);
this.titlesList = titles;
this.reqDates = reqDates;
}
@Override
public Fragment getItem(int position) {
Fragment fragment = null;
Bundle args = new Bundle();
if(fragment==null)
fragment = new IncomeWeekFragment();
if (position == 0) {
args.putString("date_start", reqDates.get(1));
args.putString("date_end", reqDates.get(0));
} else if (position == 1) {
args.putString("date_start", reqDates.get(3));
args.putString("date_end", reqDates.get(2));
} else if (position == 2) {
args.putString("date_start", reqDates.get(5));
args.putString("date_end", reqDates.get(4));
} else if (position == 3) {
args.putString("date_start", reqDates.get(7));
args.putString("date_end", reqDates.get(6));
}
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
return COUNT_INCOME_FRAGMENT;
}
@Override
public int getItemPosition(@NonNull Object object) {
return POSITION_NONE;
}
@Nullable
@Override
public CharSequence getPageTitle(int position) {
return titlesList.get(position);
}
}