如何在android中使用volley庫將數據保存到mysql？

Question

我嘗試使用本地主機中的排空庫將數據保存到mysql數據庫中。當我嘗試獲取json並向mysql添加一些數據時發生錯誤，應用程序不幸停止。示值誤差：Java.NullPointerException在該行

Controller.getInstance().addToReqQueue(request); 

這裏是我的代碼：

public class MainActivity extends AppCompatActivity { 

    EditText firstname, lastname, age; 
    Button insert, show; 
    TextView result; 
    String insertUrl = "http://192.168.56.1/android_post_api/insertStudent.php"; 
    String showUrl = "http://192.168.56.1/android_post_api/show.php"; 

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

     firstname = (EditText) findViewById(R.id.editText); 
     lastname = (EditText) findViewById(R.id.editText2); 
     age = (EditText) findViewById(R.id.editText3); 
     insert = (Button) findViewById(R.id.insert); 
     show = (Button) findViewById(R.id.showstudents); 
     result = (TextView) findViewById(R.id.textView); 
     show.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       System.out.println("ww"); 
       JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST, 
         showUrl, new Response.Listener<JSONObject>() { 
        @Override 
        public void onResponse(JSONObject response) { 
         System.out.println(response.toString()); 
         try { 
          JSONArray students = response.getJSONArray("students"); 
          for (int i = 0; i < students.length(); i++) { 
           JSONObject student = students.getJSONObject(i); 

           String firstname = student.getString("firstname"); 
           String lastname = student.getString("lastname"); 
           String age = student.getString("age"); 

           result.append(firstname + " " + lastname + " " + age + " \n"); 
          } 
          result.append("===\n"); 

         } catch (JSONException e) { 
          e.printStackTrace(); 
         } 

        } 
       }, new Response.ErrorListener() { 
        @Override 
        public void onErrorResponse(VolleyError error) { 
         System.out.append(error.getMessage()); 

        } 
       }); 
       Controller.getInstance().addToReqQueue(jsonObjectRequest); 
      } 
     }); 

     insert.setOnClickListener(new View.OnClickListener(){ 

      @Override 
      public void onClick(View v) { 
       StringRequest request = new StringRequest(Request.Method.POST, insertUrl, new Response.Listener<String>() { 
        @Override 
        public void onResponse(String response) { 
         System.out.println(response.toString()); 

        } 
       }, new Response.ErrorListener() { 

        @Override 
        public void onErrorResponse(VolleyError error) { 

        } 
       }) { 
        @Override 
        protected Map<String, String> getParams() throws AuthFailureError { 
         Map<String,String> parameters = new HashMap<String, String>(); 
         parameters.put("firstname",firstname.getText().toString()); 
         parameters.put("lastname",lastname.getText().toString()); 
         parameters.put("age",age.getText().toString()); 
         return parameters; 
        } 

       }; 
       Controller.getInstance().addToReqQueue(request); 
      } 
     }); 
    } 
    } 

Answer 1

你可以參考我下面的代碼：

 JSONObject jsonBody; 
     try { 
      jsonBody = new JSONObject(); 
      jsonBody.put("Title", "Android Volley Demo"); 
      jsonBody.put("Author", "BNK"); 
      jsonBody.put("Date", "2015/09/06"); 
      mRequestBody = jsonBody.toString(); 

     StringRequest stringRequest = new StringRequest(Request.Method.POST, url, new Response.Listener<String>() { 
      @Override 
      public void onResponse(String response) { 
       mTextView.setText(response); 
      } 
     }, new Response.ErrorListener() { 
      @Override 
      public void onErrorResponse(VolleyError error) { 
       mTextView.setText(error.toString()); 
      } 
     }) { 
      @Override 
      public String getBodyContentType() { 
       return "application/json; charset=utf-8"; 
      } 

      @Override 
      public byte[] getBody() throws AuthFailureError { 
       try { 
        return mRequestBody == null ? null : mRequestBody.getBytes("utf-8"); 
       } catch (UnsupportedEncodingException uee) { 
        VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", 
          mRequestBody, "utf-8"); 
        return null; 
       } 
      } 
     }; 
     MySingleton.getInstance(this).addToRequestQueue(stringRequest); 
    } catch (JSONException e) { 
     e.printStackTrace(); 
    } 

Answer 2

用這個代替： 在的begning您的插入功能添加以下代碼行

RequestQueue rq= Volley.newRequestQueue(this); 

和最後刪除此行的代碼從功能

Controller.getInstance().addToReqQueue(request); 

，並添加這個代替

rq.add(request);