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) {
}
}
}
This is for all those like me, which need to update the Viewpager from a service (or other background thread) and none of the proposals have worked:
After a bit of logchecking i realized, that the notifyDataSetChanged() method never returns. getItemPosition(Object object) is called an all ends there without further processing. Then i found in the docs of the parent PagerAdapter class (is not in the docs of the subclasses), "Data set changes must occur on the main thread and must end with a call to notifyDataSetChanged() ".
So, the working solution in this case was (using FragmentStatePagerAdapter
and getItemPosition(Object object) set to return POSITION_NONE) :
然后调用notifyDataSetChanged():
runOnUiThread(new Runnable() {
@Override
public void run() {
pager.getAdapter().notifyDataSetChanged();
}
});
ViewPager不是为支持动态视图更改而设计的。
我已经确认了这一点，同时寻找与此相关的另一个bug https://issuetracker.google.com/issues/36956111，特别是https://issuetracker.google.com/issues/36956111#comment56
这个问题有点老了，但是谷歌最近用ViewPager2解决了这个问题。
它将允许用标准的解决方案取代手工的(不需要维护并且可能有bug的)解决方案。它还可以防止像某些回答那样不必要地重新创建视图。
对于ViewPager2的例子，您可以查看https://github.com/googlesamples/android-viewpager2
如果您想使用ViewPager2，您需要在构建中添加以下依赖项。Gradle文件:
dependencies {
implementation 'androidx.viewpager2:viewpager2:1.0.0-beta02'
}
然后你可以替换你的ViewPager在你的xml文件:
<androidx.viewpager2.widget.ViewPager2
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />
在那之后，你需要在你的活动中用ViewPager2替换ViewPager
ViewPager2需要一个RecyclerView。适配器，或者FragmentStateAdapter，在你的例子中，它可以是RecyclerView。适配器
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
private Context context;
private ArrayList<String> arrayList = new ArrayList<>();
public MyAdapter(Context context, ArrayList<String> arrayList) {
this.context = context;
this.arrayList = arrayList;
}
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.list_item, parent, false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
holder.tvName.setText(arrayList.get(position));
}
@Override
public int getItemCount() {
return arrayList.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder {
TextView tvName;
public MyViewHolder(@NonNull View itemView) {
super(itemView);
tvName = itemView.findViewById(R.id.tvName);
}
}
}
在使用TabLayout的情况下，你可以使用TabLayoutMediator:
TabLayoutMediator tabLayoutMediator = new TabLayoutMediator(tabLayout, viewPager, true, new TabLayoutMediator.OnConfigureTabCallback() {
@Override
public void onConfigureTab(@NotNull TabLayout.Tab tab, int position) {
// configure your tab here
tab.setText(tabs.get(position).getTitle());
}
});
tabLayoutMediator.attach();
然后，您将能够通过修改适配器的数据并调用notifyDataSetChanged方法来刷新视图
