我如何从共享首选项中检索数据到片段中
How can i retrieve data from sharedpreferences into fragment
我有 SharedPrefManger class,它可以保存用户信息并检索数据,但是当我将其用于片段时 return 空指针异常
package com.example.e_learning.storage;
import android.content.Context;
import android.content.SharedPreferences;
import com.example.e_learning.jsondata.StudentData;
import com.example.e_learning.pojo.StudentModel;
public class SharedPrefManger {
private static SharedPrefManger INSTANCE;
private Context context;
private static final String SHARED_PREF_NAME = "MySharedPref";
public SharedPrefManger(Context context) {
this.context = context;
}
public static SharedPrefManger getINSTANCE(Context context) {
if (INSTANCE == null)
INSTANCE = new SharedPrefManger(context);
return INSTANCE;
}
public void saveUser(StudentData data) {
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putInt("id", data.getId());
editor.putString("email", data.getEmail());
editor.putString("name", data.getName());
editor.putString("level", data.getLevel());
editor.apply();
}
public boolean isLoggedIn() {
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
return preferences.getInt("id", -1) != -1;
}
public StudentData getUser() {
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
return new StudentData(
preferences.getInt("id", -1),
preferences.getString("name", null),
preferences.getString("email", null),
preferences.getString("level", null)
);
}
public void clear(){
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.clear();
editor.apply();
}
}
我有一个片段,我想将用户检索到其中
但是当我调用 getUser Id return null
这是我的片段
package com.example.e_learning.ui.fragments.announcement;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.ViewModelProvider;
import androidx.recyclerview.widget.LinearLayoutManager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import com.example.e_learning.R;
import com.example.e_learning.databinding.FragmentAnnouncementBinding;
import com.example.e_learning.jsondata.AnnouncementsData;
import com.example.e_learning.storage.SharedPrefManger;
import java.util.ArrayList;
/**
* A simple {@link Fragment} subclass.
*/
public class AnnouncementFragment extends Fragment {
private FragmentAnnouncementBinding binding;
private AnnouncementsViewModel announcementsViewModel;
public AnnouncementFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
binding = DataBindingUtil.inflate(inflater, R.layout.fragment_announcement, container, false);
View view = binding.getRoot();
return view;
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
AnnouncementAdapter announcementAdapter = new AnnouncementAdapter();
binding.announcementRecycler.setLayoutManager(new LinearLayoutManager(getContext()));
binding.announcementRecycler.setAdapter(announcementAdapter);
announcementsViewModel.getStudentId().setValue(SharedPrefManger.getINSTANCE(this.getActivity()).getUser().getId());
announcementsViewModel = new ViewModelProvider(requireActivity()).get(AnnouncementsViewModel.class);
announcementsViewModel.getAnnouncements();
announcementsViewModel.announcementsModelMutableLiveData.observe(getViewLifecycleOwner(), announcementsModel -> {
if (announcementsModel.getStatus()) {
announcementAdapter.setList((ArrayList<AnnouncementsData>) announcementsModel.getData());
} else if (!announcementsModel.getStatus()) {
Toast.makeText(getContext(), announcementsModel.getError(), Toast.LENGTH_SHORT).show();
}
});
}
}
这一行return空指针异常
announcementsViewModel.getStudentId().setValue(SharedPrefManger.getINSTANCE(this.getActivity()).getUser().getId());
如何将用户数据检索到此片段中?
这个 class 与其他活动一起使用效果很好
使用前必须先初始化announcementsViewModel
所以需要移动此行
announcementsViewModel = new ViewModelProvider(requireActivity()).get(AnnouncementsViewModel.class);
在此之前
announcementsViewModel.getStudentId().setValue(SharedPrefManger.getINSTANCE(this.getActivity()).getUser().getId());
创建 class 共享首选项的对象,具有构造函数。
以及您想要获取它的位置,只需使用 new 关键字和该首选项名称方法调用构造函数即可。
像:
新 PrefManager(getActivity).getData();
我有 SharedPrefManger class,它可以保存用户信息并检索数据,但是当我将其用于片段时 return 空指针异常
package com.example.e_learning.storage;
import android.content.Context;
import android.content.SharedPreferences;
import com.example.e_learning.jsondata.StudentData;
import com.example.e_learning.pojo.StudentModel;
public class SharedPrefManger {
private static SharedPrefManger INSTANCE;
private Context context;
private static final String SHARED_PREF_NAME = "MySharedPref";
public SharedPrefManger(Context context) {
this.context = context;
}
public static SharedPrefManger getINSTANCE(Context context) {
if (INSTANCE == null)
INSTANCE = new SharedPrefManger(context);
return INSTANCE;
}
public void saveUser(StudentData data) {
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putInt("id", data.getId());
editor.putString("email", data.getEmail());
editor.putString("name", data.getName());
editor.putString("level", data.getLevel());
editor.apply();
}
public boolean isLoggedIn() {
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
return preferences.getInt("id", -1) != -1;
}
public StudentData getUser() {
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
return new StudentData(
preferences.getInt("id", -1),
preferences.getString("name", null),
preferences.getString("email", null),
preferences.getString("level", null)
);
}
public void clear(){
SharedPreferences preferences = context.getSharedPreferences(SHARED_PREF_NAME, Context.MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.clear();
editor.apply();
}
}
我有一个片段,我想将用户检索到其中 但是当我调用 getUser Id return null
这是我的片段
package com.example.e_learning.ui.fragments.announcement;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.ViewModelProvider;
import androidx.recyclerview.widget.LinearLayoutManager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import com.example.e_learning.R;
import com.example.e_learning.databinding.FragmentAnnouncementBinding;
import com.example.e_learning.jsondata.AnnouncementsData;
import com.example.e_learning.storage.SharedPrefManger;
import java.util.ArrayList;
/**
* A simple {@link Fragment} subclass.
*/
public class AnnouncementFragment extends Fragment {
private FragmentAnnouncementBinding binding;
private AnnouncementsViewModel announcementsViewModel;
public AnnouncementFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
binding = DataBindingUtil.inflate(inflater, R.layout.fragment_announcement, container, false);
View view = binding.getRoot();
return view;
}
@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
AnnouncementAdapter announcementAdapter = new AnnouncementAdapter();
binding.announcementRecycler.setLayoutManager(new LinearLayoutManager(getContext()));
binding.announcementRecycler.setAdapter(announcementAdapter);
announcementsViewModel.getStudentId().setValue(SharedPrefManger.getINSTANCE(this.getActivity()).getUser().getId());
announcementsViewModel = new ViewModelProvider(requireActivity()).get(AnnouncementsViewModel.class);
announcementsViewModel.getAnnouncements();
announcementsViewModel.announcementsModelMutableLiveData.observe(getViewLifecycleOwner(), announcementsModel -> {
if (announcementsModel.getStatus()) {
announcementAdapter.setList((ArrayList<AnnouncementsData>) announcementsModel.getData());
} else if (!announcementsModel.getStatus()) {
Toast.makeText(getContext(), announcementsModel.getError(), Toast.LENGTH_SHORT).show();
}
});
}
}
这一行return空指针异常
announcementsViewModel.getStudentId().setValue(SharedPrefManger.getINSTANCE(this.getActivity()).getUser().getId());
如何将用户数据检索到此片段中? 这个 class 与其他活动一起使用效果很好
使用前必须先初始化announcementsViewModel
所以需要移动此行
announcementsViewModel = new ViewModelProvider(requireActivity()).get(AnnouncementsViewModel.class);
在此之前
announcementsViewModel.getStudentId().setValue(SharedPrefManger.getINSTANCE(this.getActivity()).getUser().getId());
创建 class 共享首选项的对象,具有构造函数。 以及您想要获取它的位置,只需使用 new 关键字和该首选项名称方法调用构造函数即可。 像: 新 PrefManager(getActivity).getData();