試圖訪問SQLite表的活動中的空錯誤

Question

新手提問時間再次; 因此，在FormActivity中，我發佈然後從遠程服務器上的SQL表接收響應，數據將被放入本地SQLite錶行中。然後，我有一個包含多個EditText字段的片段，我嘗試用本地表格數據填充。現在，我在Activity，DrawText（）中有一個方法來做到這一點，但是當運行時，我正在崩潰。我放入的logcat消息顯示，當DrawText（）被調用時，它從SQLite表中提取的值爲null。

我已經移動該方法，試圖確保它已經從服務器響應填充後訪問表，但無法使其工作。任何幫助將不勝感激。下面的代碼（現在編輯的幫助）

FormActivity.java

public class FormActivity extends FragmentActivity { 

    //create variables & Logcat tag 
    private static final String TAG = FormActivity.class.getSimpleName(); 
    private EditText inputTitle; 
    private EditText inputName; 
    private EditText inputSurname; 
    private SessionManager sm; 
    private SQLiteHandler db; 
    private ProgressDialog pDialog; 
    private String e_check; 
    private String surname; 

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

     //set inputs for fields 
     inputTitle = (EditText) findViewById(R.id.titleText); 
     inputName = (EditText) findViewById(R.id.foreText); 
     inputSurname = (EditText) findViewById(R.id.surnameText); 

     //initialise pager for swipe screens 
     ViewPager pager = (ViewPager) findViewById(R.id.viewPager); 
     pager.setAdapter(new MyPagerAdapter(getSupportFragmentManager())); 

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

     //email value passed in 
     Bundle extras = getIntent().getExtras(); 
     if (extras != null) { 
      e_check = extras.getString("e_check"); 
     } 

     // SQLite database handler - delete old and recreate db from remote server data 
     db = new SQLiteHandler(getApplicationContext()); 

     String email = e_check; 
     checkUserDetails(email); 
     //<!-- TODO: load db fields to textfields --> 
     //<!-- TODO: greeting toast --> 
    } 
    /** 
    * function to verify & retrieve details in mysql db 
    * */ 
    private void checkUserDetails(final String email) { 
     // Tag used to cancel the request 
     String tag_string_req = "req_retrieve"; 

     pDialog.setMessage("Retrieving details ..."); 
     showDialog(); 

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

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

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

        // Check for error node in json 
        if (!error) { 
         // user exists 
         // fill in textfields 
         String uid = jObj.getString("uid"); 

         JSONObject user = jObj.getJSONObject("user"); 
         String name = user.getString("name"); 
         surname = user.getString("surname"); 
         String email = user.getString("email"); 
         String created_at = user 
           .getString("created_at"); 
         String tel_no = user.getString("tel_no"); 
         String home_add = user.getString("home_add"); 
         String postcode = user.getString("postcode"); 
         String postal = user.getString("postal"); 

         // Inserting row in table 
         db.addUser(name, surname, email, uid, created_at, tel_no, home_add, postcode, postal); 

         final Handler handler = new Handler(); 
         handler.postDelayed(new Runnable() { 
          @Override 
          public void run() { 
           //Do something after 300ms 
           DrawText(); 
          } 
         }, 300); 

         /* Displaying the user details on the screen 
         FirstFragment fragA = (FirstFragment) getSupportFragmentManager().findFragmentByTag("fragA"); 
         fragA.DrawText();*/ 

        } 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(); 
       } 

      } 
     }, new Response.ErrorListener() { 

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

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

       return params; 
      } 
     }; 

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

    public void DrawText() { 
     // Fetching user details from sqlite 
     HashMap<String, String> user = db.getUserDetails(); 

     if (user.size() != 0) { 
      //String surname = user.get("surname"); 
      Log.e(TAG, "string surname: " + surname); 

      // Displaying the user details on the screen 
      inputSurname.setText(surname); 
     }else{ 
      Log.e(TAG, "something you want to say"); 
     } 
    } 

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

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

    private class MyPagerAdapter extends FragmentPagerAdapter { 

     public MyPagerAdapter(FragmentManager fm) { 
      super(fm); 
     } 

     @Override 
     public Fragment getItem(int pos) { 
      switch(pos) { 

       case 0: return FirstFragment.newInstance("FirstFragment, Instance 1"); 
       case 1: return SecondFragment.newInstance("SecondFragment, Instance 1"); 
       case 2: return ThirdFragment.newInstance("ThirdFragment, Instance 1"); 
       case 3: return FourthFragment.newInstance("FourthFragment, Instance 1"); 
       //case 4: return FifthFragment.newInstance("ThirdFragment, Instance 3"); 
       default: return FirstFragment.newInstance("FirstFragment, Default"); 

      } 
     } 

     @Override 
     // Number of screens we want to swipe between 
     public int getCount() { 
      return 4; 
     } 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_form, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 
} 

logcat的（還更新）

05-16 09:31:35.560 21981-21981/com.disclosure_scots.disclosure_scots D/FormActivity﹕ Retrieval Response: {"tag":"retrieve","error":false,"uid":"55558b80341dc0.72266271","user":{"name":"John","surname":"Carter","email":"cart@email.com","created_at":"2015-05-15 08:00:32","tel_no":"1231234123","home_add":"22 Lone Road","postcode":"G44 4TT","postal":"false"}} 
05-16 09:31:35.643 21981-21981/com.disclosure_scots.disclosure_scots D/SQLiteHandler﹕ Database tables created 
05-16 09:31:35.663 21981-21981/com.disclosure_scots.disclosure_scots D/SQLiteHandler﹕ New user inserted into sqlite: 1 
05-16 09:31:35.980 21981-21981/com.disclosure_scots.disclosure_scots D/SQLiteHandler﹕ Fetching user from Sqlite: {tel_no=1231234123, postal=false, email=cart@email.com, surname=Carter, name=John, created_at=2015-05-15 08:00:32, uid=55558b80341dc0.72266271, home_add=22 Lone Road, postcode=G44 4TT} 
05-16 09:31:35.980 21981-21981/com.disclosure_scots.disclosure_scots E/FormActivity﹕ string surname: Carter 
05-16 09:31:35.980 21981-21981/com.disclosure_scots.disclosure_scots D/AndroidRuntime﹕ Shutting down VM 
05-16 09:31:35.981 21981-21981/com.disclosure_scots.disclosure_scots E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.disclosure_scots.disclosure_scots, PID: 21981 
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.EditText.setText(java.lang.CharSequence)' on a null object reference 
      at com.disclosure_scots.disclosure_scots.FormActivity.DrawText(FormActivity.java:180) 
      at com.disclosure_scots.disclosure_scots.FormActivity$1$1.run(FormActivity.java:125) 
      at android.os.Handler.handleCallback(Handler.java:739) 
      at android.os.Handler.dispatchMessage(Handler.java:95) 
      at android.os.Looper.loop(Looper.java:135) 
      at android.app.ActivityThread.main(ActivityThread.java:5257) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:372) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

Answer 1

的問題是，你想添加數據之前收集數據。正如您所看到的，在接收到響應之後（在將數據添加到數據庫之前），您正在調用DrawText();。所以顯然數據將是空的。將數據添加到數據庫後，應該調用DrawText();。

db.addUser(name, surname, email, uid, created_at, tel_no, home_add, postcode, postal); 
DrawText(); 

如果上面的代碼不能正常工作，請嘗試使用500毫秒後調用DrawText的（）這樣的

db.addUser(name, surname, email, uid, created_at, tel_no, home_add, postcode, postal); 
final Handler handler = new Handler(); 
handler.postDelayed(new Runnable() { 
    @Override 
    public void run() { 
    //Do something after 500ms 
    DrawText(); 
    } 
}, 500); 

如果沒有從上面的工作。在方法之外聲明字符串變量，如名稱，姓氏等（從JSON中解析出來），這些方法將擴展變量對任何方法的可訪問性並更新DrawText（）;這樣

private String surname; 

.....{ 
    .... 
    surname = jsonObject.getString("surname"); 
    ... 
} 

public void DrawText() { 
     Log.e(TAG, "string surname: " + surname); 

     // Displaying the user details on the screen 
     inputSurname.setText(surname); 
    } 

Answer 2

public void DrawText() { 
    // Fetching user details from sqlite 
    HashMap<String, String> user = db.getUserDetails(); 
if (user.size() != 0) { 
    String surname = user.get("surname"); 
    Log.e(TAG, "string surname: " + surname); 

    // Displaying the user details on the screen 
    inputSurname.setText(surname); 
}else{ 
Log.e(TAG, "something you want to say");} 

}