如何在SharedPreferene中存储JSON返回值

Question

我正在收到android应用程序崩溃问题。其实我试图将json的返回值存储在Android应用程序的sharedPreference中。哪些没有错误，但应用程序是继续崩溃，我尝试多次卸载应用程序，并没有progress.I不知道错误，再次我是新的共享首选项实际上这个应用程序使用sqllite之前我改变它。 我试图存储JSON返回数据在sharedpreferance这里是我的loginActivity文件：

import android.app.Activity; 
import android.app.ProgressDialog; 
import android.content.Intent; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.Toast; 

import com.android.volley.Request.Method; 
import com.android.volley.Response; 
import com.android.volley.VolleyError; 
import com.android.volley.toolbox.StringRequest; 

import org.json.JSONException; 
import org.json.JSONObject; 

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

import info.androidhive.loginandregistration.R; 
import info.androidhive.loginandregistration.app.AppConfig; 
import info.androidhive.loginandregistration.app.AppController; 
import info.androidhive.loginandregistration.helper.SQLiteHandler; 
import info.androidhive.loginandregistration.helper.SessionManager; 

public class LoginActivity extends Activity { 
    private static final String TAG = RegisterActivity.class.getSimpleName(); 
    private Button btnLogin; 
    private Button btnLinkToRegister; 
    private EditText inputEmail; 
    private EditText inputPassword; 
    private ProgressDialog pDialog; 
    private SessionManager session; 
    private SQLiteHandler db; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_login); 

     inputEmail = (EditText) findViewById(R.id.email); 
     inputPassword = (EditText) findViewById(R.id.password); 
     btnLogin = (Button) findViewById(R.id.btnLogin); 
     btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen); 

     // Progress dialog 
     pDialog = new ProgressDialog(this); 
     pDialog.setCancelable(false); 

     // SQLite database handler 
     db = new SQLiteHandler(getApplicationContext()); 

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

     // Check if user is already logged in or not 
     if (session.isLoggedIn()) { 
      // User is already logged in. Take him to main activity 
      Intent intent = new Intent(LoginActivity.this, MainActivity.class); 
      startActivity(intent); 
      finish(); 
     } 

     // Login button Click Event 
     btnLogin.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       String email = inputEmail.getText().toString().trim(); 
       String password = inputPassword.getText().toString().trim(); 

       // Check for empty data in the form 
       if (!email.isEmpty() && !password.isEmpty()) { 
        // login user 
        checkLogin(email, password); 
       } else { 
        // Prompt user to enter credentials 
        Toast.makeText(getApplicationContext(), 
          "Please enter the credentials!", Toast.LENGTH_LONG) 
          .show(); 
       } 
      } 

     }); 

     // Link to Register Screen 
     btnLinkToRegister.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       Intent i = new Intent(getApplicationContext(), 
         RegisterActivity.class); 
       startActivity(i); 
       finish(); 
      } 
     }); 

    } 

    /** 
    * function to verify login details in mysql db 
    * */ 
    private void checkLogin(final String email, final String password) { 
     // Tag used to cancel the request 
     String tag_string_req = "req_login"; 

     pDialog.setMessage("Logging in ..."); 
     showDialog(); 

     StringRequest strReq = new StringRequest(Method.POST, 
       AppConfig.URL_LOGIN, new Response.Listener<String>() { 

      @Override 
      public void onResponse(String response) { 
       Log.d(TAG, "Login Response: " + response.toString()); 
       hideDialog(); 

       try { 
        JSONObject jObj = new JSONObject(response); 
        boolean error = jObj.getBoolean("error"); 

        // Check for error node in json 
        if (!error) { 
         // user successfully logged in 
         // Create login session 
         session.checkLogin(); 

         // Now store the user in SQLite 
         String uid = jObj.getString("uid"); 

         JSONObject user = jObj.getJSONObject("user"); 
         int id = user.getInt("id"); 
         String name = user.getString("name"); 
         String email = user.getString("email"); 
         String status = user.getString("status"); 

         session.createLoginSession(email,password,id); 
         Intent intent = new Intent(LoginActivity.this, 
           MainActivity.class); 
         intent.putExtra("status",status); 
         startActivity(intent); 
         finish(); 
        } else { 
         // Error in login. Get the error message 
         String errorMsg = jObj.getString("error_msg"); 
         Toast.makeText(getApplicationContext(), 
           errorMsg, Toast.LENGTH_LONG).show(); 
        } 
       } catch (JSONException e) { 
        // JSON error 
        e.printStackTrace(); 
        Toast.makeText(getApplicationContext(), "Json error: " + e.getMessage(), Toast.LENGTH_LONG).show(); 
       } 

      } 
     }, new Response.ErrorListener() { 

      @Override 
      public void onErrorResponse(VolleyError error) { 
       Log.e(TAG, "Login Error: " + error.getMessage()); 
       Toast.makeText(getApplicationContext(), 
         error.getMessage(), Toast.LENGTH_LONG).show(); 
       hideDialog(); 
      } 
     }) { 

      @Override 
      protected Map<String, String> getParams() { 
       // Posting parameters to login url 
       Map<String, String> params = new HashMap<String, String>(); 
       params.put("email", email); 
       params.put("password", password); 

       return params; 
      } 

     }; 

     // Adding request to request queue 
     AppController.getInstance().addToRequestQueue(strReq, tag_string_req); 
    } 

    private void showDialog() { 
     if (!pDialog.isShowing()) 
      pDialog.show(); 
    } 

    private void hideDialog() { 
     if (pDialog.isShowing()) 
      pDialog.dismiss(); 
    } 
} 

和SessionManager是：

import android.content.Context; 
import android.content.Intent; 
import android.content.SharedPreferences; 
import android.content.SharedPreferences.Editor; 
import android.util.Log; 

import java.util.HashMap; 

import info.androidhive.loginandregistration.activity.LoginActivity; 

public class SessionManager { 
    // LogCat tag 
    private static String TAG = SessionManager.class.getSimpleName(); 
    // Shared Preferences 
    SharedPreferences pref; 
    Editor editor; 
    Context _context; 
    // Shared pref mode 
    int PRIVATE_MODE = 1; 

    // Shared preferences file name 
    private static final String PREF_NAME = "OnlineShop"; 
    private static final String KEY_IS_LOGGED_IN = "isLoggedIn"; 
    // Email address (make variable public to access from outside) 
    public static final String KEY_EMAIL = "email"; 

    // Password (make variable public to access from outside) 
    public static final String KEY_PASS = "password"; 

    //ID userid for the session 
    public static final String KEY_ID="uid"; 



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

    /** 
    * Create login session 
    * */ 
    public void createLoginSession(String email, String password, int uid){ 
     // Storing login value as TRUE 
     editor.putBoolean(KEY_IS_LOGGED_IN, true); 

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

     // Storing password in pref 
     editor.putString(KEY_PASS, password); 

     //Storing userid uid in pref 
     editor.putInt(KEY_ID, uid); 
     // commit changes 
     editor.commit(); 
    } 

/* public void setLogin(boolean isLoggedIn) { 
     editor.putBoolean(KEY_IS_LOGGED_IN, isLoggedIn); 
     editor.commit(); 
     Log.d(TAG, "User login session modified!"); 
    } 
    */ 
    /** 
    * 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, LoginActivity.class); 
      // Closing all the Activities 
      i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 

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

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

    } 
    /** 
    * Get stored session data 
    * */ 
    public HashMap<String, String> getUserDetails(){ 
     HashMap<String, String> user = new HashMap<String, String>(); 
     // user email 
     user.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null)); 

     // user password 
     user.put(KEY_PASS, pref.getString(KEY_PASS, null)); 

     //user id 
     user.put(KEY_ID, pref.getString(KEY_ID, 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, LoginActivity.class); 
     // Closing all the Activities 
     i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 

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

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


    public boolean isLoggedIn(){ 

     return pref.getBoolean(KEY_IS_LOGGED_IN, true); 
    } 
} 

错误

03-07 19:26:27.643 1795-1795/? E/AndroidRuntime: FATAL EXCEPTION: main Process: 
info.androidhive.loginandregistration, 
PID: 1795 java.lang.RuntimeException: 
Unable to start activity ComponentInfo{info.androidhive.loginandregistration/info.androidhive.loginandreg‌​istration.activity.MainActivity}: 
     java.lang.NullPointerException: Attempt to invoke virtual method 
     'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference 

Answer 1

这与存储JSON值无关SharedPreferences。发生崩溃的原因不同。在你的MainActivity中，你试图读取Bundle的内容，特别是“status”的值，但问题是当你调用MainActivity的时候，你并不总是把这个额外的值，而且很可能你没有检查在尝试读取它之前是否为空。在一个地方，你调用它为：

Intent intent = new Intent(LoginActivity.this, MainActivity.class); 
startActivity(intent); 

而在另一个为：

Intent intent = new Intent(LoginActivity.this, MainActivity.class); 
intent.putExtra("status",status); 
startActivity(intent); 

因此，实现一些正确的错误在您的MainActivity处理，你应该摆脱这种崩溃。

Answer 2

 public class SharedPreference { 
      private SharedPreferences mPrefs; 
      private Context mContext; 
      private String KEY = "KEY"; 
      private String JSONKEY = "JSONKEY"; 


      public SharedPreference(Context mContext) { 
       this.mContext = mContext; 
       mPrefs = PreferenceManager.getDefaultSharedPreferences(mContext); 
      } 

     // for saving list in JSON format 
      public boolean setList(List<String> list) 
      { 
       SharedPreferences.Editor prefsEditor = mPrefs.edit(); 
       Gson gson = new Gson(); 
       String json = gson.toJson(list); 
       prefsEditor.putString(KEY, json); 
       return prefsEditor.commit(); 
      } 
     // get list from json format 
      public List<String> getList() 
      { 
       Gson gson = new Gson(); 
       String json = mPrefs.getString(KEY, ""); 
       Type type = new TypeToken<ArrayList<String>>() {}.getType(); 
       return gson.fromJson(json,type); 
      } 


     // Set Json 
      public boolean setJson(JSONObject json) 
      { 
       SharedPreferences.Editor prefsEditor = mPrefs.edit(); 
       String jsonString = json.toString(); 
       prefsEditor.putString(JSONKEY, jsonString); 
       return prefsEditor.commit(); 
      } 

     // get json 
      public JSONObject getJson() throws JSONException { 
       Gson gson = new Gson(); 
       String json = mPrefs.getString(JSONKEY, ""); 

       return new JSONObject(json); 
      } 


     } 

你应该得到的字符串就像下面以避免空指针异常

// string can be null 
    String status = getIntent().getStringExtra("status"); 

if(status!= null) 
{ 
// do your work here 
}