Question

我正在开发一个使用服务的Android应用程序。我从该服务获取信息并将json数据保存到arraylist中它没关系，但我需要来自另一个类的这些数据。我试图访问此数组列表，但每次尝试时它都为null。这是我的代码：

我要将此列表称为“

”的类

public class AllVehicles extends android.app.Fragment {
public ArrayList<Vehicle> vehicleList= new ArrayList<Vehicle>();
public AllVehicles() {}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);       
    GetAllVehicles getAllVehicles=new GetAllVehicles();
    getAllVehicles.execute("tr101", member.getAuthToken().toString(), String.valueOf(member.getMemberId()), String.valueOf(member.getFirmId()));
}
//onPostExecute of async task
 protected void onPostExecute(Long result) {
            try {
                JSONObject jsonObj = new JSONObject(response_vehicles);
                JSONArray jsonArray = jsonObj.getJSONArray("VehicleOnlineList");                      
                for (int i = 0; i < jsonArray.length(); i++) {
                    vehicle = new Vehicle();
                    vehicle_report=new Vehicle();
                    JSONArray jsonArr = jsonArray.getJSONArray(i);
                    vehicle.setVehicleId(jsonArr.isNull(0) ? 0 : jsonArr.getInt(0));
                    vehicle.setDeviceId(jsonArr.isNull(1) ? 0 : jsonArr.getInt(1));
                    vehicle.setPlate(jsonArr.isNull(2) ? "" : jsonArr.getString(2));
                    vehicle.setVehicleName(jsonArr.isNull(3) ? "" : jsonArr.getString(3));
                    vehicleList.add(vehicle);               
                }
//The method for calling vehicleList:
public ArrayList<Vehicle> getVehicleReportList(){
        return vehicleList;
    }

Answer 1

public static ArrayList<Vehicle> vehicleList= new ArrayList<Vehicle>();

并在您想要使用的地方使用AllVehicles.vehicleList。

Answer 2

使用回调的标准方式：创建一个iterface，在片段中实现并将其上下文发送到AsyncTask类

以下是示例：

import android.content.Context;
import android.os.AsyncTask;

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

import java.util.ArrayList;

/**
 * Created by Ramesh Kumar on 2/16/2016.
 */
public class AsycTaskTest extends
        AsyncTask<String, String, ArrayList<Object>> {

    Context activity;


    InterfaceResult operations;

    public AsycTaskTest(Context activity, InterfaceResult operations) {
        this.operations = operations;
        this.activity = activity;
    }

    @Override
    protected void onProgressUpdate(String... values) {
        // TODO Auto-generated method stub
        super.onProgressUpdate(values);
        // new ProgressBar(Appli)
    }

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
    }

    @Override
    protected void onPostExecute(ArrayList<Object> result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        if (operations != null)
            operations.onSuccess(result);
    }


    @Override
    protected ArrayList<Object> doInBackground(String... params) {
        // TODO Auto-generated method stub

        ArrayList<Vehical>   vehicleList =new ArrayList<>();
        try {
            //your code to access response_vehicles


            JSONObject jsonObj = new JSONObject(response_vehicles);
            JSONArray jsonArray = jsonObj.getJSONArray("VehicleOnlineList");
            for (int i = 0; i < jsonArray.length(); i++) {
                Vehicle vehicle = new Vehicle();
                JSONArray jsonArr = jsonArray.getJSONArray(i);
                vehicle.setVehicleId(jsonArr.isNull(0) ? 0 : jsonArr.getInt(0));
                vehicle.setDeviceId(jsonArr.isNull(1) ? 0 : jsonArr.getInt(1));
                vehicle.setPlate(jsonArr.isNull(2) ? "" : jsonArr.getString(2));
                vehicle.setVehicleName(jsonArr.isNull(3) ? "" : jsonArr.getString(3));
                vehicleList.add(vehicle);
            }

//        return list;
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return vehicleList;

    }

接口：

public interface InterfaceResult {
    void onSuccess(ArrayList<Object> result);
}

当你在片段中实现它时，必须覆盖InterfaceResult的方法，数据将传递给Fragment的onSuccess并执行你想要的。

如果你不能得到任何东西，请随时提出。

如何从另一个类访问填充asynctask的列表视图？

2 个答案: