为什么重新打开应用程序时我的 SharedPreferences 登录字符串值为空？

Question

我还是安卓新手。我已经用 android 创建了登录应用程序，用户可以登录该应用程序。用户成功登录后，然后直接进入主页活动。我的首选项值（我使用电子邮件作为字符串值）保存得很好，并且我的注销按钮运行良好。我尝试按 Android 设备模拟器中的“主页”按钮，然后再次运行应用程序，效果很好。该应用程序可以恢复我的家庭活动中的偏好值并显示电子邮件。我的问题是，当我按下设备模拟器中的后退按钮时，应用程序关闭，我尝试再次打开我的应用程序，显示主页活动，但不加载我的首选项值字符串（电子邮件），也不显示上次登录用户的电子邮件。你能告诉我为什么吗？用户登录应用程序后如何保留我的偏好值（电子邮件字符串）？

这是我的代码： SessionManager.java

package com.agungphe.simplelogreg;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;

import java.util.HashMap;

public class SessionManager extends Activity {
    // Shared Preferences
    SharedPreferences pref;

    // Editor for Shared preferences
    SharedPreferences.Editor editor;

    // Context
    Context _context;

    // Shared pref mode
    int PRIVATE_MODE = 0;

    // Sharedpref file name
    private static final String PREF_NAME = "PirjaRSMS";

    // All Shared Preferences Keys
    private static final String IS_LOGIN = "IsLoggedIn";

    // Email address (make variable public to access from outside)
    public static final String KEY_EMAIL = "email";

    // Constructor
    public SessionManager(Context context){
        this._context = context;
        pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
        editor = pref.edit();
    }

    /**
     * Create login session
     *
     * @param email*/
    public void createLoginSession(String email){
        // Storing login value as TRUE
        editor.putBoolean(IS_LOGIN, true);

        // Storing email in pref
        editor.putString(KEY_EMAIL, email);

        // commit changes
        editor.commit();
    }

    /**
     * Check login method wil check user login status
     * If false it will redirect user to login page
     * Else won't do anything
     * */
    public void checkLogin(){
        // Check login status
        if(!this.isLoggedIn()){
            // user is not logged in redirect him to Login Activity
            Intent i = new Intent(_context, Login.class);
            // Closing all the Activities
            i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);

            // Add new Flag to start new Activity
            i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

            // Staring Login Activity
            _context.startActivity(i);
            finish();
        }

    }

    /**
     * Get stored session data
     * */
    public HashMap<String, String> getUserDetails(){
        HashMap<String, String> user = new HashMap<String, String>();

        // user email id
        user.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null));

        // return user
        return user;
    }

    /**
     * Clear session details
     * */
    public void logoutUser(){
        // Clearing all data from Shared Preferences
        editor.clear();
        editor.commit();

        // After logout redirect user to Loing Activity
        Intent i = new Intent(_context, Login.class);
        // Closing all the Activities
        i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);

        // Add new Flag to start new Activity
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

        // Staring Login Activity
        _context.startActivity(i);
    }

    /**
     * Quick check for login
     * **/
    // Get Login State
    public boolean isLoggedIn(){
        return pref.getBoolean(IS_LOGIN, false);
    }
}

登录.java

package com.agungphe.simplelogreg;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import java.util.HashMap;
import java.util.Map;

public class Login extends AppCompatActivity implements View.OnClickListener {

    public static final String LOGIN_URL = "http://182.168.6.77/api_pirja/login.php";

    public static final String KEY_EMAIL="email";
    public static final String KEY_PASSWORD="password";

    private EditText editTextEmail;
    private EditText editTextPassword;
    private Button buttonLogin;

    private String email;
    private String password;

    // Session Manager Class
    SessionManager session;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Session Manager
        session = new SessionManager(getApplicationContext());

        if(session.isLoggedIn() == true){
            setContentView(R.layout.activity_home);
        }
        else {
            setContentView(R.layout.activity_login);

            editTextEmail = (EditText) findViewById(R.id.editTextEmail);
            editTextPassword = (EditText) findViewById(R.id.editTextPassword);

//            Toast.makeText(getApplicationContext(), "User Login Status: " + session.isLoggedIn(), Toast.LENGTH_LONG).show();

            buttonLogin = (Button) findViewById(R.id.button);

            buttonLogin.setOnClickListener(this);
        }
    }


    private void userLogin() {
        email = editTextEmail.getText().toString().trim();
        password = editTextPassword.getText().toString().trim();

        StringRequest stringRequest = new StringRequest(Request.Method.POST, LOGIN_URL,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        if(response.trim().equals("success")){
                            session.createLoginSession(email);
                            openHome();
                        }
                        else if(response.trim().equals("blm_aktif")){
                            openVerifikasi();
                        }
                        else{
                            Toast.makeText(Login.this,response,Toast.LENGTH_LONG).show();
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(Login.this,error.toString(),Toast.LENGTH_LONG ).show();
                    }
                }){
            @Override
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String,String> map = new HashMap<String,String>();
                map.put(KEY_EMAIL,email);
                map.put(KEY_PASSWORD,password);
                return map;
            }
        };

        RequestQueue requestQueue = Volley.newRequestQueue(this);
        requestQueue.add(stringRequest);
    }

    private void openHome(){
        Intent intent = new Intent(this, Home.class);
        startActivity(intent);
        finish();
    }

    private void openVerifikasi(){
        Intent intent = new Intent(this, Verifikasi.class);
        startActivity(intent);
        finish();
    }

    @Override
    public void onClick(View v) {
        userLogin();
    }

    public void keRegister(View view){
        Intent intent = new Intent(this, Register.class);
        startActivity(intent);
    }
}

Home.java

package com.agungphe.simplelogreg;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.HashMap;

public class Home extends AppCompatActivity {

    // Session Manager Class
    SessionManager session;

    // Button Logout
    Button btnLogout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Session class instance
        session = new SessionManager(getApplicationContext());

        session.checkLogin();

        // get user data from session
        HashMap<String, String> user = session.getUserDetails();

        // email
        String email = user.get(SessionManager.KEY_EMAIL);

        setContentView(R.layout.activity_home);

        TextView lblEmail = (TextView) findViewById(R.id.lblEmail);

        // Button logout
        btnLogout = (Button) findViewById(R.id.btnLogout);

        // displaying user data
        lblEmail.setText(email);

    }

    public void logOut(View view){
        session.logoutUser();
        finish();
     }
}

谢谢您的提前:)

Answer 1

从Activity的Android生命周期来看，

^{（图片来源于活动生命周期）}

您实现了 onPause 和 onResume 方法吗？因为按后退按钮不会关闭 Activity，而是进入暂停状态。在 onResume 中执行 setText 可以解决您的问题。

这是您的简历：

@Override
public void onResume() {
    super.onResume();  // Always call the superclass method first

    // You'll have to run the code to retrieve your user details, and set all of them to their relative widgets.
}