关于 android：即使在 Fragment 分离后也显示 Toast 消息？

Show Toast message even after Fragment has been detached?

我的应用程序使用带有几个菜单项的导航抽屉，这些菜单项基本上可以打开不同的片段。每个片段可以运行一个 AsyncTask，之后显示 Toast 消息。但是，当用户在另一个片段正在运行时尝试打开一个片段时，我会收到一个空指针错误，这是可以理解的，因为原始片段已被分离。

但是，即使在那时也有可能举行 Toast 表演吗？当在导航器上单击项目时，我基本上有此代码。

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public void setFragment(Fragment fragment) {
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.content, fragment)
.commit();
}

然后在片段上只是一个简单的 asynctask，它在 PostExecute 上显示 Toast 消息。

1	Toast.makeText(getContext(), t.getLocalizedMessage(), Toast.LENGTH_LONG).show();

感谢任何帮助。

更新(2018 年 3 月 28 日)

我尝试使用监听器，它似乎工作。

我基本上有一个 BaseFragment，我的所有片段都在其中扩展。我只是在其中添加了一个回调。

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public class BaseFragment extends Fragment {

private OnToast callback;

@Override
public void onAttach(Context context) {
super.onAttach(context);
try {
callback = (BaseFragment.OnToast) context;
} catch (ClassCastException e) {
throw new ClassCastException(context.toString() +" must implement OnAuthenticateListener");
}
}

public OnToast getCallback() {
return callback;
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
setHasOptionsMenu(true);
}

public interface OnToast {
void toast(String message);
}
}

在我的实际片段中，我有：

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public class JailsFragment extends BaseFragment {

private List<Jail> jailList = new ArrayList<>();

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setTitle("Jails");
setAdapter(new JailAdapter());

if (savedInstanceState == null) {
onSwipeRefresh();
}

}

@Override
public void onSwipeRefresh() {
super.onSwipeRefresh();
setRefreshing(true);
jailList.clear();
FreeNAS.getInstance().getJails().getJails(new Callback<List<Jail>>() {
@Override
public void onResponse(Call<List<Jail>> call, Response<List<Jail>> response) {
if (response.code() == 200) {
jailList.addAll(response.body());
notifyDatasetChanged();
} else {
//Toast.makeText(getContext(), response.message(), Toast.LENGTH_LONG).show();
getCallback().toast(response.message());
}
setRefreshing(false);
}

@Override
public void onFailure(Call<List<Jail>> call, Throwable t) {
//Toast.makeText(getContext(), t.getLocalizedMessage(), Toast.LENGTH_LONG).show();
getCallback().toast(t.getLocalizedMessage());
setRefreshing(false);
}
});
}

}

然后在我的 MainActivity 中：

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public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener, BaseFragment.OnToast {

private SharedPreferences pref;
private Toolbar toolbar;
private DrawerLayout drawer;
private ActionBarDrawerToggle toggle;
private NavigationView navigationView;

@Override
public void toast(String message) {
Toast.makeText(getApplicationContext(), message, Toast.LENGTH_LONG).show();
}

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

pref = PreferenceManager.getDefaultSharedPreferences(this);

toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();

navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);

if (savedInstanceState == null) {
setFragment(new AuthenticateFragment());
}

}

@Override
public void onBackPressed() {
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.

final int id = item.getItemId();

drawer.closeDrawer(GravityCompat.START);
drawer.postDelayed(new Runnable() {
@Override
public void run() {

if (id == R.id.nav_plugins) {
setFragment(new PluginsFragment());
} else if (id == R.id.nav_jails) {
setFragment(new JailsFragment());
} else if (id == R.id.nav_jails_configuration) {
setFragment(new ConfigurationFragment());
} else if (id == R.id.nav_services) {
setFragment(new ServicesFragment());
} else if (id == R.id.nav_alerts) {
setFragment(new AlertsFragment());
} else if (id == R.id.nav_updates) {
setFragment(new UpdatesFragment());
}
}
}, 300);

return true;
}

public void setFragment(Fragment fragment) {
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.content, fragment)
.commit();
}

}