我正在使用兼容性库中的ViewPager。我已经成功地让它显示几个视图，我可以通过页面。
但是，我很难弄清楚如何用一组新的视图更新ViewPager。
我已经尝试了各种各样的事情，比如调用mAdapter.notifyDataSetChanged()， mviewpage .invalidate()，甚至在每次我想使用新的数据列表时创建一个全新的适配器。
没有任何帮助，textviews保持不变，从原始数据。
更新:
我做了一个小测试项目，我几乎能够更新视图。我将在下面粘贴这个类。
然而，似乎没有更新的是第二个视图，“B”仍然存在，它应该在按下更新按钮后显示“Y”。
public class ViewPagerBugActivity extends Activity {
private ViewPager myViewPager;
private List<String> data;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
data = new ArrayList<String>();
data.add("A");
data.add("B");
data.add("C");
myViewPager = (ViewPager) findViewById(R.id.my_view_pager);
myViewPager.setAdapter(new MyViewPagerAdapter(this, data));
Button updateButton = (Button) findViewById(R.id.update_button);
updateButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
updateViewPager();
}
});
}
private void updateViewPager() {
data.clear();
data.add("X");
data.add("Y");
data.add("Z");
myViewPager.getAdapter().notifyDataSetChanged();
}
private class MyViewPagerAdapter extends PagerAdapter {
private List<String> data;
private Context ctx;
public MyViewPagerAdapter(Context ctx, List<String> data) {
this.ctx = ctx;
this.data = data;
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object instantiateItem(View collection, int position) {
TextView view = new TextView(ctx);
view.setText(data.get(position));
((ViewPager)collection).addView(view);
return view;
}
@Override
public void destroyItem(View collection, int position, Object view) {
((ViewPager) collection).removeView((View) view);
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
@Override
public Parcelable saveState() {
return null;
}
@Override
public void restoreState(Parcelable arg0, ClassLoader arg1) {
}
@Override
public void startUpdate(View arg0) {
}
@Override
public void finishUpdate(View arg0) {
}
}
}
你可以动态更新所有的片段，你可以在三个步骤中看到。
在适配器中:
public class MyPagerAdapter extends FragmentPagerAdapter {
private static int NUM_ITEMS = 3;
private Map<Integer, String> mFragmentTags;
private FragmentManager mFragmentManager;
public MyPagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
mFragmentManager = fragmentManager;
mFragmentTags = new HashMap<Integer, String>();
}
// Returns total number of pages
@Override
public int getCount() {
return NUM_ITEMS;
}
// Returns the fragment to display for that page
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return FirstFragment.newInstance();
case 1:
return SecondFragment.newInstance();
case 2:
return ThirdFragment.newInstance();
default:
return null;
}
}
// Returns the page title for the top indicator
@Override
public CharSequence getPageTitle(int position) {
return "Page " + position;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
Object object = super.instantiateItem(container, position);
if (object instanceof Fragment) {
Fragment fragment = (Fragment) object;
String tag = fragment.getTag();
mFragmentTags.put(position, tag);
}
return object;
}
public Fragment getFragment(int position) {
Fragment fragment = null;
String tag = mFragmentTags.get(position);
if (tag != null) {
fragment = mFragmentManager.findFragmentByTag(tag);
}
return fragment;
}}
现在在你的活动中:
public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener{
MyPagerAdapter mAdapterViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager viewPager = (ViewPager) findViewById(R.id.vpPager);
mAdapterViewPager = new MyPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapterViewPager);
viewPager.addOnPageChangeListener(this);
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
Fragment fragment = mAdapterViewPager.getFragment(position);
if (fragment != null) {
fragment.onResume();
}
}
@Override
public void onPageScrollStateChanged(int state) {
}}
最后在你的片段中，是这样的:
public class YourFragment extends Fragment {
// newInstance constructor for creating fragment with arguments
public static YourFragment newInstance() {
return new YourFragment();
}
// Store instance variables based on arguments passed
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
// Inflate the view for the fragment based on layout XML
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment, container, false);
}
@Override
public void onResume() {
super.onResume();
//to refresh your view
refresh();
}}
您可以在这里看到完整的代码。
谢谢阿尔瓦罗·路易斯·布斯塔曼特。
在OP提出他的问题两年半之后，这个问题仍然，嗯，仍然是一个问题。显然谷歌在这方面的优先级不是特别高，所以我没有找到解决方案，而是找到了一个变通办法。对我来说，最大的突破是找到了问题的真正原因(见本文中公认的答案)。一旦问题明显是任何活动页面都没有正确刷新，我的解决方法就很明显了:
在我的片段(几页)中:
I took all the code which populates the form out of onCreateView and put it in a function called PopulateForm which may be called from anywhere, rather than by the framework. This function attempts to get the current View using getView, and if that is null, it just returns. It's important that PopulateForm contains only the code that displays - all the other code which creates FocusChange listeners and the like is still in OnCreate
Create a boolean which can be used as a flag indicating the form must be reloaded. Mine is mbReloadForm
Override OnResume() to call PopulateForm() if mbReloadForm is set.
在我的活动中，我做页面的加载:
Go to page 0 before changing anything. I'm using FragmentStatePagerAdapter, so I know that two or three pages are affected at most. Changing to page 0 ensures I only ever have the problem on pages 0, 1 and 2.
Before clearing the old list, take it's size(). This way you know how many pages are affected by the bug. If > 3, reduce it to 3 - if you're using a a different PagerAdapter, you'll have to see how many pages you have to deal with (maybe all?)
Reload the data and call pageAdapter.notifyDataSetChanged()
Now, for each of the affected pages, see if the page is active by using pager.getChildAt(i) - this tells you if you have a view. If so, call pager.PopulateView(). If not, set the ReloadForm flag.
在此之后，当您重新加载第二组页面时，该错误仍然会导致一些页面显示旧数据。但是，现在它们将被刷新，您将看到新的数据-您的用户不会知道页面是不正确的，因为这种刷新将在他们看到页面之前发生。
希望这能帮助到一些人!
alvarolb给出的答案绝对是最好的方法。基于他的回答，实现这一点的一个简单方法是简单地按位置存储活动视图:
SparseArray<View> views = new SparseArray<View>();
@Override
public Object instantiateItem(View container, int position) {
View root = <build your view here>;
((ViewPager) container).addView(root);
views.put(position, root);
return root;
}
@Override
public void destroyItem(View collection, int position, Object o) {
View view = (View)o;
((ViewPager) collection).removeView(view);
views.remove(position);
view = null;
}
然后，一旦覆盖notifyDataSetChanged方法，您就可以刷新视图…
@Override
public void notifyDataSetChanged() {
int key = 0;
for(int i = 0; i < views.size(); i++) {
key = views.keyAt(i);
View view = views.get(key);
<refresh view with new data>
}
super.notifyDataSetChanged();
}
实际上，您可以在instantiateItem和notifyDataSetChanged中使用类似的代码来刷新视图。在我的代码中，我使用了完全相同的方法。
你只需要这段简单的代码:
代码:
private void updateAdapter() {
if (adapterViewPager != null) {
int from = vpMyViewPager.getCurrentItem() - vpMyViewPager.getOffscreenPageLimit();
int to = vpMyViewPager.getCurrentItem() + vpMyViewPager.getOffscreenPageLimit();
vpMyViewPager.removeAllViews();
for (int i = from; i <= to; i++) {
if (i < 0) {
continue;
}
adapterViewPager.instantiateItem(vpMyViewPager, i);
}
}
}
解释:
If you haven't changed offscreenPageLimit of the ViewPager, it always has 3 to 4 children depending on which direction you are going. And in order to show the correct content inside its children, it uses the adapter to get the right content.
now when you call removeAllViews() on your ViewPager, only 3 to 4 Views are actually being removed from the Window's hierarchy, and by calling instantiateItem(ViewGroup viewPager, int index), you are only recreating 3 to 4 Views. Then everything is back to normal, you swipe and scroll, the ViewPager shows contents using its adapter. The number of its children is not the same on all devices in all situations, for example if you set the offscreenPageLimit to 5, it will probably have around 11 to 12 children, but that's all, it's not much. it's fast.
