應用程序崩潰時試圖創建新的記錄在遠程數據庫mysql使用凌空

Question

我已經創建了一個簡單的Android應用程序連接到遠程SQL數據庫..問題是當我點擊註冊應用程序崩潰。請幫我傢伙

package com.example.akshay.webservices; 

/** 
* Created by Akshay on 7/20/2015. 
*/ 
import com.example.akshay.webservices.AppConfig; 
import com.example.akshay.webservices.AppController; 
import com.example.akshay.webservices.SQLiteHandler; 
import com.example.akshay.webservices.SessionManager; 

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

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

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; 

public class RegisterActivity extends Activity { 
    private static final String TAG = RegisterActivity.class.getSimpleName(); 
    private Button btnRegister; 
    private Button btnLinkToLogin; 
    private EditText inputFullName; 
    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_register); 

     inputFullName = (EditText) findViewById(R.id.name); 
     inputEmail = (EditText) findViewById(R.id.email); 
     inputPassword = (EditText) findViewById(R.id.password); 
     btnRegister = (Button) findViewById(R.id.btnRegister); 
     btnLinkToLogin = (Button) findViewById(R.id.btnLinkToLoginScreen); 

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

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

     // SQLite database handler 
     db = new SQLiteHandler(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(RegisterActivity.this, 
        MainActivity.class); 
      startActivity(intent); 
      finish(); 
     } 

     // Register Button Click event 
     btnRegister.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View view) { 
       String name = inputFullName.getText().toString(); 
       String email = inputEmail.getText().toString(); 
       String password = inputPassword.getText().toString(); 

       if (!name.isEmpty() && !email.isEmpty() && !password.isEmpty()) { 
        registerUser(name, email, password); 
       } else { 
        Toast.makeText(getApplicationContext(), 
          "Please enter your details!", Toast.LENGTH_LONG) 
          .show(); 
       } 
      } 
     }); 

     // Link to Login Screen 
     btnLinkToLogin.setOnClickListener(new View.OnClickListener() { 

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

    } 

    /** 
    * Function to store user in MySQL database will post params(tag, name, 
    * email, password) to register url 
    * */ 
    private void registerUser(final String name, final String email, 
           final String password) { 
     // Tag used to cancel the request 
     String tag_string_req = "req_register"; 

     pDialog.setMessage("Registering ..."); 
     showDialog(); 

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

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

       try { 
        JSONObject jObj = new JSONObject(response); 
        boolean error = jObj.getBoolean("error"); 
        if (!error) { 
         // User successfully stored in MySQL 
         // Now store the user in sqlite 
         String uid = jObj.getString("uid"); 

         JSONObject user = jObj.getJSONObject("user"); 
         String name = user.getString("name"); 
         String email = user.getString("email"); 
         String created_at = user 
           .getString("created_at"); 

         // Inserting row in users table 
         db.addUser(name, email, uid, created_at); 

         // Launch login activity 
         Intent intent = new Intent(
           RegisterActivity.this, 
           LoginActivity.class); 
         startActivity(intent); 
         finish(); 
        } else { 

         // Error occurred in registration. Get the error 
         // message 
         String errorMsg = jObj.getString("error_msg"); 
         Toast.makeText(getApplicationContext(), 
           errorMsg, Toast.LENGTH_LONG).show(); 
        } 
       } catch (JSONException e) { 
        e.printStackTrace(); 
       } 

      } 
     }, new Response.ErrorListener() { 

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

      @Override 
      protected Map<String, String> getParams() { 
       // Posting params to register url 
       Map<String, String> params = new HashMap<String, String>(); 
       params.put("tag", "register"); 
       params.put("name", name); 
       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(); 
    } 
} 

AppController.java

package com.example.akshay.webservices; 

import android.app.Application; 

/** 
* Created by Akshay on 7/19/2015. 
*/ 
import android.app.Application; 
import android.text.TextUtils; 

import com.android.volley.Request; 
import com.android.volley.RequestQueue; 
import com.android.volley.toolbox.Volley; 

public class AppController extends Application { 

    public static final String TAG = AppController.class.getSimpleName(); 

    private RequestQueue mRequestQueue; 

    private static AppController mInstance; 

    @Override 
    public void onCreate() { 
     super.onCreate(); 
     mInstance = this; 
    } 

    public static synchronized AppController getInstance() { 
     return mInstance; 
    } 

    public RequestQueue getRequestQueue() { 
     if (mRequestQueue == null) { 
      mRequestQueue = Volley.newRequestQueue(getApplicationContext()); 
     } 

     return mRequestQueue; 
    } 

    public <T> void addToRequestQueue(Request<T> req, String tag) { 
     req.setTag(TextUtils.isEmpty(tag) ? TAG : tag); 
     getRequestQueue().add(req); 
    } 

    public <T> void addToRequestQueue(Request<T> req) { 
     req.setTag(TAG); 
     getRequestQueue().add(req); 
    } 

    public void cancelPendingRequests(Object tag) { 
     if (mRequestQueue != null) { 
      mRequestQueue.cancelAll(tag); 
     } 
    } 
} 

的logcat：

07-20 20:27:07.195 8233-8233/? E/Zygote﹕ MountEmulatedStorage() 
07-20 20:27:07.195 8233-8233/? E/Zygote﹕ v2 
07-20 20:27:07.195 8233-8233/? E/SELinux﹕ [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL 
07-20 20:27:18.355 8233-8233/com.example.akshay.webservices E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.example.akshay.webservices, PID: 8233 
    java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.akshay.webservices.AppController.addToRequestQueue(com.android.volley.Request, java.lang.String)' on a null object reference 
      at com.example.akshay.webservices.RegisterActivity.registerUser(RegisterActivity.java:185) 
      at com.example.akshay.webservices.RegisterActivity.access$300(RegisterActivity.java:32) 
      at com.example.akshay.webservices.RegisterActivity$1.onClick(RegisterActivity.java:81) 
      at android.view.View.performClick(View.java:5191) 
      at android.view.View$PerformClick.run(View.java:20916) 
      at android.os.Handler.handleCallback(Handler.java:739) 
      at android.os.Handler.dispatchMessage(Handler.java:95) 
      at android.os.Looper.loop(Looper.java:145) 
      at android.app.ActivityThread.main(ActivityThread.java:5972) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:372) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 

這是我無法理解發生了什麼的logcat的。請幫助..

Answer 1

問題發生的原因AppController.getInstance（）它返回NULL， 你必須改變你的AppController.getInstance（）方法是這樣的：

public static AppController getInstance() { 
    if (mInstance == null) { 
     mInstance = new AppController; 
    } 
    return mInstance; 
} 

也確保您在您的清單被註冊您的應用類 你應該有一個像這樣在你的清單應用程序的屬性：

<application 
     android:name="package.AppController" <-------- 
     android:allowBackup="true" 
     android:debuggable="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="xyz" 
     android:screenOrientation="landscape" 
     android:theme="@style/AppTheme"> 

此處瞭解詳情：http://developer.android.com/reference/android/app/Application.html

「需要維護全局應用程序狀態的基類。 你可以通過在你的AndroidManifest.xml標籤中指定它的名字來提供你自己的實現，當你的應用程序/包的進程被創建時，這會導致你的類被實例化。 「

Answer 2

嘿，我有同樣的問題，當我試圖這個解決方案也最終沒有工作，我得到了一條出路。

爲什麼它返回一個空指針的問題，因爲這些方法的getInstance（）和getRequestQueue （）沒有返回任何關於上下文的信息，爲了解決這個問題，首先在公共類AppController中擴展Application private context myContext。背景

public AppController(Context context){ 
    myContext = context; 
    mRequestQueue = getRequestQueue(); 
} 

STEP 2.修改hyou getInstance（）方法的上下文中工作如下：

public static synchronized AppController getInstance(Context context) { 

     if(mInstance==null){ 
     mInstance = new AppController(context); 
     } 
     return mInstance; 
    } 

步驟3. 最後修改getRequestQueue（）方法的上下文中工作如下

public RequestQueue getRequestQueue() { 
     if (mRequestQueue == null) { 
      mRequestQueue = Volley.newRequestQueue(myContext.getApplicationContext()); 
     } 

     return mRequestQueue; 
    } 
Finally got the calling class and call the methods from AppController.java with respect to the context of the activity or broadcaster. 

AppController.getInstance(this).addToRequestQueue(strReq, tag_string_req);