我创建了一个带标签活动的应用。我有3个标签，在第一个标签中我添加了一个RecyclerView。起初一切正常。但是当我现在启动应用程序时，片段是空的。甚至第二和第三个标签的片段都是空的，我只放置了一个TextView。以下是来自MainActivity的代码，它主要是从Android Studio生成的，我只添加了一些代码来更改工具栏标题并更改了一些小东西：
public class MainActivity extends AppCompatActivity {
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
private Toolbar toolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitle("Pflege");
setSupportActionBar(toolbar);
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
tabLayout.getTabAt(0).setIcon(R.drawable.tab_icon_pflege);
tabLayout.getTabAt(1).setIcon(R.drawable.tab_icon_dokumentation);
tabLayout.getTabAt(2).setIcon(R.drawable.tab_icon_probleme);
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
switch(tab.getPosition()) {
case 0:
mViewPager.setCurrentItem(0);
toolbar.setTitle("Pflege");
break;
case 1:
mViewPager.setCurrentItem(1);
toolbar.setTitle("Daten");
break;
case 2:
mViewPager.setCurrentItem(2);
toolbar.setTitle("Probleme");
break;
default:
mViewPager.setCurrentItem(tab.getPosition());
toolbar.setTitle("Pflege");
break;
}
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
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) {
switch(position){
case 0:
Tab1Pflege tab1 = new Tab1Pflege();
return tab1;
case 1:
Tab2Dokumentation tab2 = new Tab2Dokumentation();
return tab2;
case 2:
Tab3Probleme tab3 = new Tab3Probleme();
return tab3;
default:
return null;
}
}
@Override
public int getCount() {
// Show 3 total pages.
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Pflege";
case 1:
return "Daten";
case 2:
return "Probleme";
}
return null;
}
}
}
这是MainActivity的XML文件。我稍微改了一下，标签将放在屏幕的底部：
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="eis1617.muellerkimmeyer.app.MainActivity">
<android.support.design.widget.AppBarLayout
android:id="@+id/appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="@dimen/appbar_padding_top"
android:theme="@style/AppTheme.AppBarOverlay"
android:background="#3f84dd">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_scrollFlags="scroll|enterAlways"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<android.support.v4.view.ViewPager
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
android:layout_above="@+id/tabs" />
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
android:elevation="80dp"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.design.widget.TabLayout
android:id="@+id/tabs"
android:layout_width="match_parent"
android:layout_height="56dp"
android:clickable="true"
app:tabGravity="fill"
app:tabIndicatorHeight="0dp"
app:tabMode="fixed"
app:tabBackground="@drawable/tab_color_selector"
android:background="#3f84dd"/>
</android.support.design.widget.AppBarLayout>
</android.support.design.widget.CoordinatorLayout>
现在这是第一个标签的片段。它包含RecyclerView：
public class Tab1Pflege extends Fragment {
private RecyclerView recyclerView;
private RecyclerView.Adapter rvAdapter;
private RecyclerView.LayoutManager rvLayoutManager;
private ArrayList<String> listItems;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.tab1_pflege, container, false);
listItems = new ArrayList<>();
listItems.add("Test1");
listItems.add("Test2");
listItems.add("Test3");
recyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerView);
rvLayoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(rvLayoutManager);
rvAdapter = new RvAdapter(listItems);
recyclerView.setAdapter(rvAdapter);
return rootView;
}
}
这是该选项卡的XML文件：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="eis1617.muellerkimmeyer.app.MainActivity">
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/recyclerView"
/>
</RelativeLayout>
这里是列表项的XML文件。左侧有一个TextView，右侧有一个ImageView：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="50dp"
android:background="?attr/selectableItemBackground">
<TextView
android:text="TextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/itemTitle"
android:layout_marginLeft="21dp"
android:layout_marginStart="21dp"
android:layout_centerVertical="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:textSize="20sp" />
<ImageView
android:layout_width="50dp"
android:layout_height="50dp"
android:id="@+id/itemImage"
android:layout_marginRight="11dp"
android:layout_marginEnd="11dp"
android:layout_centerVertical="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
</RelativeLayout>
最后这是我的RecyclerView的Adapter类：
public class RvAdapter extends RecyclerView.Adapter<RvAdapter.MyViewHolder> {
ArrayList<String> listItems;
public RvAdapter (ArrayList<String> listItems){
this.listItems = listItems;
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.rv_item_layout, null);
return new MyViewHolder(itemView);
}
@Override
public void onBindViewHolder(MyViewHolder holder, final int position) {
holder.itemTitle.setText(listItems.get(position));
holder.itemImage.setImageResource(R.drawable.ic_keyboard_arrow_right);
}
@Override
public int getItemCount() {
return listItems.size();
}
public class MyViewHolder extends RecyclerView.ViewHolder{
TextView itemTitle;
ImageView itemImage;
public MyViewHolder(View itemView){
super(itemView);
itemTitle = (TextView) itemView.findViewById(R.id.itemTitle);
itemImage = (ImageView) itemView.findViewById(R.id.itemImage);
}
}
}
我已经尝试用“extends FragmentStatePagerAdapter”替换MainActivity中的“extends FragmentPagerAdapter”。但碎片仍然是空的。有人知道可能是什么问题吗？有时当我在XML文件中为列表项更改某些内容时，它会再次起作用。但是，当我重新启动应用程序时，它不再起作用了。如果它起作用，它看起来是随机的。