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對於Android而言，新的Im和dev試圖連接服務器並獲取Json響應的應用程序，將其解析爲類並使其可用。嘗試在空對象引用上調用接口方法<MyInterfaceMethord>參考
伊夫implimented 3類此
- 公共類客戶{}
- 公共類ServerConnect {}
- 公共類JsonParser {}
的Serverconnect使用凌空庫下載異步線程上的網頁源代碼。下載後，Server Connect類啓動一個onServerResponded（String responce）列表器。這個響應是JsonParser類的輸入。在JsonParser類成功獲取客戶列表之後，它激發另一個名爲onCustomersParsed（List customers）的列表器。稍後處理在onCustomersParsed回調內完成。
但即時得到一個致命的異常..
嘗試調用接口方法 '無效 app.utilities.JsonParser $ OnCustomersParserListner.onCustomersParsed（）' 上的空對象引用
我盡力而爲，但失敗了。這裏是我的代碼
package app.elements;
/**
* Created by Sangeeth Nandakumar on 13-02-2017.
*/
public class Customer
{
private String id;
private String firstname;
private String lastname;
private String device;
private String gender;
public Customer(String id, String firstname, String lastname, String device,String gender)
{
this.id = id;
this.firstname = firstname;
this.lastname = lastname;
this.device = device;
this.gender = gender;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getFirstname() {
return firstname;
}
public void setFirstname(String firstname) {
this.firstname = firstname;
}
public String getLastname() {
return lastname;
}
public void setLastname(String lastname) {
this.lastname = lastname;
}
public String getDevice() {
return device;
}
public void setDevice(String device) {
this.device = device;
}
}
THIS IS MY服務器連接器類
package app.utilities;
import android.content.Context;
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;
/**
* Created by Sangeeth Nandakumar on 18-02-2017.
* Highly optimised Google's Volley driven async webpage source downloader
*/
public class ServerConnector
{
//Member variables
private Context context;
//Override interfaces
public interface OnServerStatusListner
{
public void onServerResponded(String responce);
public void onServerRevoked();
}
//New listner
private OnServerStatusListner listner;
//Listner function
public void setOnServerStatusListner(OnServerStatusListner myststus)
{
listner=myststus;
}
//Constructor
public ServerConnector(Context context)
{
this.context = context;
}
//Connect to server
public void connectServer(String url)
{
//Create a request queue
RequestQueue queue= Volley.newRequestQueue(context);
//Tunnel the request
StringRequest stringRequest=new StringRequest(Request.Method.GET, url,
//When request success
new Response.Listener<String>()
{
@Override
public void onResponse(String response)
{
listner.onServerResponded(response);
}
},
//When request fails
new Response.ErrorListener()
{
@Override
public void onErrorResponse(VolleyError error)
{
listner.onServerRevoked();
}
});
//Add the request to queue
queue.add(stringRequest);
}
}
THIS IS MY JSON解析器類
package app.utilities;
import android.content.Context;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
import app.elements.Customer;
/**
* Created by Sangeeth Nandakumar on 18-02-2017.
* Highly optimised Json parserclass with multiple listners
*/
public class JsonParser
{
//Data members
private Context context;
private String jsontext;
private List<Customer> customers=new ArrayList<>();
//Listner object
public OnCustomersParserListner listner;
//Listners
public interface OnCustomersParserListner
{
public void onCustomersParsed(List<Customer> customers);
}
//On Jsonparse listner
public void setOnJsonParseListner(OnCustomersParserListner mylistner)
{
listner=mylistner;
}
//Constructor
public JsonParser(Context context, String jsontext)
{
this.context = context;
this.jsontext = jsontext;
}
//Json pre-parsing
public void parseCustomers()
{
// If json is true
if (jsontext != null)
{
try
{
//Create a JSON object
JSONObject jsonObj = new JSONObject(jsontext);
// Getting JSON Array node
JSONArray json = jsonObj.getJSONArray("details");
// Looping through All Contacts
for (int i = 0; i < json.length(); i++)
{
JSONObject details = json.getJSONObject(i);
//Get all customer details from JSON file
String id = details.getString("id");
String firstname = details.getString("firstname");
String lastname = details.getString("lastname");
String device = details.getString("device");
String gender = details.getString("gender");
//Add to list
customers.add(new Customer(id,firstname,lastname,device,gender));
}
listner.onCustomersParsed(customers);
}
catch (final JSONException e)
{
Toast.makeText(context, "Error in parsing JSON", Toast.LENGTH_SHORT).show();
}
}
else
{
Toast.makeText(context, "JSON text is empty", Toast.LENGTH_SHORT).show();
}
}
}
這一點與主要活動通話
ServerConnector server=new ServerConnector(this);
server.connectServer("http://amazinginside.esy.es/customerlist.php");
server.setOnServerStatusListner(new ServerConnector.OnServerStatusListner()
{
@Override
public void onServerResponded(String responce)
{
Toast.makeText(MainActivity.this, "Server responded", Toast.LENGTH_SHORT).show();
JsonParser parser=new JsonParser(getApplicationContext(),responce);
parser.parseCustomers();
parser.setOnJsonParseListner(new JsonParser.OnCustomersParserListner() {
@Override
public void onCustomersParsed(List<Customer> customers) {
Toast.makeText(MainActivity.this, customers.get(0).getFirstname(), Toast.LENGTH_SHORT).show();
}
});
}
@Override
public void onServerRevoked()
{
Toast.makeText(MainActivity.this, "Connection to server broke", Toast.LENGTH_SHORT).show();
}
});
任何人都可以幫我
嘗試更改設置偵聽程序的順序並在MainActivity中調用parseCustomers。 – Sanjeet