我正在尝试使用一个包含导航视图的独特活动，其选项将打开另一个片段。一切正常，除非从另一个片段（从导航视图中打开）返回时重新创建MainFragment。我想知道如何避免这种情况，因为它再次加载了列表。
主要活动：
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
toolbar.setTitle(R.string.home);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
getSupportFragmentManager().beginTransaction()
.add(R.id.layout, new MainFragment())
.commit();
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.getMenu().findItem(R.id.nav_home).setChecked(true);
getSupportFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
getSupportFragmentManager().popBackStack();
}
switch (item.getItemId()) {
case R.id.nav_history:
getSupportFragmentManager().beginTransaction()
.replace(R.id.layout, new Fragment2())
.addToBackStack(null)
.commit();
break;
case R.id.nav_settings:
break;
case R.id.nav_logout:
break;
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
主要片段：
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.DividerItemDecoration;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ProgressBar;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import br.com.example.adapters.ScheduledServicesAdapter;
import br.com.example.entities.ScheduledService;
public class MainFragment extends Fragment {
private final class ScheduleServiceTask extends AsyncTask<Void, Void, List<ScheduledService>> {
@Override
protected List<ScheduledService> doInBackground(Void... params) {
mList = new ArrayList<>();
mList.add(new ScheduledService(new Date(), 250.50, 0));
mList.add(new ScheduledService(new Date(), 50.75, 0));
return mList;
}
@Override
protected void onPostExecute(List<ScheduledService> scheduledServices) {
super.onPostExecute(scheduledServices);
setData(scheduledServices);
}
}
private RecyclerView mRecyclerView;
private ScheduledServicesAdapter mAdapter;
private List<ScheduledService> mList;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
super.onCreateView(inflater, parent, savedInstanceState);
return inflater.inflate(R.layout.content_main, parent, false);
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(getActivity(),
linearLayoutManager.getOrientation());
mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(linearLayoutManager);
mRecyclerView.addItemDecoration(dividerItemDecoration);
new ScheduleServiceTask().execute();
}
private void setData(List<ScheduledService> list) {
ProgressBar progressBar = (ProgressBar) getActivity().findViewById(R.id.progress_bar);
progressBar.setVisibility(View.GONE);
if (!list.isEmpty()) {
mAdapter = new ScheduledServicesAdapter(list);
mRecyclerView.setAdapter(mAdapter);
} else {
TextView emptyText = (TextView) getActivity().findViewById(R.id.empty_text);
emptyText.setVisibility(View.VISIBLE);
}
}
}
片段2具有用于测试目的的hello world文本视图。
最佳答案
当您将MainFragment放入BackStack时（表示该视图fragment的visible不是Fragment2，因为onCreateView
屏幕），则属于该视图的所有视图都将被销毁。
然后，当您从另一个片段返回MainFragment时，
MainFragment将被重新创建。这意味着onViewCreated和new ScheduleServiceTask().execute();将是
再次打电话。
对于您的情况，我建议：
将onCreate移到requestGetData()或
另一种方法（例如：mAdapter）
初始化adapter并将mRecyclerView设置为onViewCreated()
在setData()方法上，您所需要做的就是为mAdapter重置数据并调用notifyDatasetChanged()函数。
关于android - Android-如何避免按下后退按钮时重新创建 fragment ，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/43600793/