Java Android：从随机片段/活动访问用户登录数据

我正在开发一个应用程序，我正在尝试（但失败）在一系列活动和片段之间传递数据。目前，我有一些登录/注册活动，它们工作得很好，可以将用户的凭据保存在在线MySqli数据库上，当用户登录时，一些凭据会传递给主活动，主活动包含一个显示片段的容器

我使用一个bundle将数据从这个主活动传递到它的一个片段没有任何问题，但是，现在我有几个子页面链接到一个概要文件片段，它们是按以下顺序访问的：MainScreen-ProfileFragment-EditProfileFragment-ChangeUserName（一个弹出式活动）。EditProfile框架也有一个changeUserPicture按钮，但它将使用与名称更改相同的方法

我需要将用户的凭据从MainScreen传递到ChangeUserName活动。我曾经尝试过使用一个捆绑链，在创建活动/片段时传递字符串，但没有正常工作

我正在尝试使用一个接口来传递这些数据，但我无法确定如何正确地传递，在此方面的任何帮助都将不胜感激

相关活动和片段的代码如下：

主屏幕：

public class MainScreen extends FragmentActivity implements View.OnClickListener {

ImageButton homeButton, searchButton, messageButton, contactsButton;
ImageView Luna;
ConstraintLayout homeView, searchView, lunaView, inboxView, contactsView;

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

    final ImageButton homeButton = (ImageButton) findViewById(R.id.bottom_home);
    final ImageButton searchButton = (ImageButton) findViewById(R.id.bottom_search);
    final ImageView Luna = (ImageView) findViewById(R.id.bottom_luna);
    final ImageButton messageButton = (ImageButton) findViewById(R.id.bottom_messages);
    final ImageButton contactsButton = (ImageButton) findViewById(R.id.bottom_contacts);

    final ConstraintLayout homeView = (ConstraintLayout) findViewById(R.id.home_section);
    final ConstraintLayout searchView = (ConstraintLayout) findViewById(R.id.search_section);
    final ConstraintLayout lunaView = (ConstraintLayout) findViewById(R.id.luna_section);
    final ConstraintLayout inboxView = (ConstraintLayout) findViewById(R.id.inbox_section);
    final ConstraintLayout contactsView = (ConstraintLayout) findViewById(R.id.contacts_section);

    final ImageButton profileButton = (ImageButton) findViewById(R.id.profile_button);

    final TextView titleBarText = (TextView) findViewById(R.id.titleText);

    homeView.setOnClickListener(this);
    searchView.setOnClickListener(this);
    lunaView.setOnClickListener(this);
    inboxView.setOnClickListener(this);
    contactsView.setOnClickListener(this);

    if (findViewById(R.id.container) != null) {

        if (savedInstanceState != null) {
            return;
        }

        HomeFragment firstFragment = new HomeFragment();
        firstFragment.setArguments(getIntent().getExtras());
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, firstFragment)
                .commit();
        titleBarText.setText("Home");

    }


    /*  This is the old toolbar button code. Keep just in case

    homeView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.container, new HomeFragment());
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
        }
    });

    */
    Intent intent = getIntent();
    final Integer user_id = intent.getIntExtra("user_id", 0);
    final String name = intent.getStringExtra("name");
    final String email = intent.getStringExtra("email");

    profileButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Fragment profileFragment = new ProfileFragment();

            Bundle profileBundle = new Bundle();
            profileBundle.putInt("idKey", user_id);
            profileBundle.putString("nameKey", name);
            profileBundle.putString("emailKey", email);

            profileFragment.setArguments(profileBundle);

            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.container, profileFragment);
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
        }
    });

}

@Override
public void onClick(View view) {
    Fragment fragment = new Fragment();
    switch (view.getId()){
        case R.id.home_section:
            fragment = new HomeFragment();

            break;
        case R.id.search_section:
            fragment = new SearchFragment();

            break;
        case R.id.luna_section:
            fragment = new LunaFragment();

            break;
        case R.id.inbox_section:
            fragment = new MessageFragment();

             break;
        case R.id.contacts_section:
            fragment = new ContactsFragment();

            break;
    }
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.container, fragment);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
}

@Override
public void onBackPressed()
{
    if(getFragmentManager().getBackStackEntryCount() > 0)
        getFragmentManager().popBackStack();
    else
        super.onBackPressed();
}

}

ProfileFragment：

public class ProfileFragment extends Fragment{

MainScreen activity = (MainScreen) getActivity();

public ProfileFragment() {
}

    @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_profile, container, false);
        final TextView userName = (TextView) view.findViewById(R.id.userFullName);
        final TextView userWorkplace = (TextView) view.findViewById(R.id.workplace);

        final Button workspaceButton = (Button) view.findViewById(R.id.workspaceButton);
        final Button socialButton = (Button) view.findViewById(R.id.socialspaceButton);
        final Button editProfileButton = (Button) view.findViewById(R.id.editProfileButton);
        final Button preferencesButton = (Button) view.findViewById(R.id.preferencesButton);
        final Button appSettingsButton = (Button) view.findViewById(R.id.appSettingsButton);

        Bundle interfaceBundle = this.getArguments();


        if (interfaceBundle != null) {
            String nameBundle = getArguments().getString("nameKey"); //Get pass data with its key value
            userName.setText(nameBundle);
        } else {
            userName.setText("No Username Found");
        }

        editProfileButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FragmentManager fragmentManager = getFragmentManager();
                FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.container, new EditProfileFragment());
                fragmentTransaction.addToBackStack(null);
                fragmentTransaction.commit();
            }
        });

    return view;
}





    @Override
public void onResume() {
    super.onResume();
    TextView title = (TextView) getActivity().findViewById(R.id.titleText);
    title.setText("Profile");

    ImageButton icon = (ImageButton) getActivity().findViewById(R.id.profile_button);
    icon.setColorFilter(getResources().getColor(R.color.coolWhite));
}

@Override
public void onPause() {
    super.onPause();
    ImageButton icon = (ImageButton) getActivity().findViewById(R.id.profile_button);
    icon.setColorFilter(getResources().getColor(R.color.slightGrey));
}

}

EditProfileFragment（目前仅包含两个按钮）：

}

PopupNameChange（打开以更改用户名的活动。它会在屏幕中央的片段上方弹出，并且不会覆盖以前的视图）：

---

}因此，实现目标的最快方法是使用

共享参考资料。链接到谷歌。基本上，当您在主活动中获取数据时，将该数据插入
SharedReferences
，如下所示：

SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putString("userName", userName);
editor.commit();

并在您的
中更改用户名
以获取当前用户名：

SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
String userName = sharedPref.getString("userName", defaultValue);

我也应该警告你。不要将敏感数据保存在
SharedReferences
中。有根手机的用户很容易从
SharedReferences
获取数据，我得到了一个nullPointerException，还有一些其他的SharedReferences，比如GetDefaultSharedReferences。主活动中的数据插入在onCreate方法中，而名称更改中的数据读取代码不在onCreate中，这会有区别吗？不管怎样，我添加了getApplicationContext（）而不是getActivity（），它允许我将其放在名称更改活动的onCreate中。谢谢你的帮助！！
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putString("userName", userName);
editor.commit();

SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
String userName = sharedPref.getString("userName", defaultValue);