无法解析 android 工作室中的 json，它在一个 activity 而不是另一个工作室中工作

Question

我有这个 Json，我在我的应用程序的第一个 activity 上解析了它，但是当我尝试在另一个 activity 上用相同的 json 重新创建相同的东西时=]，它只是行不通。

我一直在阅读有关此内容和空指针的内容，以查看是否可以看到在哪里可以解决此问题，但我没有想法。由于我在其他活动中还有很多 Json 需要阅读，但我无法完成其中的一项工作，所以我无法完成其余的工作。

当我调用 getData 时，我输入了一个函数、用户名和密码，它们又将成为 url 的一部分，它为我提供了 json 内容以及我尝试访问的位置读取和解析。

这是主要内容Activity：

public class MainActivity extends AppCompatActivity
{
Button logindaapp; // Botão de Login
EditText username; // Secção username
EditText password; // Secção password

private String user;
private String pass;

User userEntry = null;

ArrayList<CarDataset> carsDataset = new ArrayList<>();

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

    // Botão Login
    logindaapp = (Button) findViewById(R.id.btn_login); // Associa o id do botão

    logindaapp.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        { // Quando é clicado o botão
            disableButton(v);
            String funcao = "wslogin";
            username = (EditText)findViewById(R.id.et_username);
            user = username.getText().toString();
            password = (EditText)findViewById(R.id.et_password);
            pass = password.getText().toString();
            getData(funcao, user, pass);

        }
    });
}

String mLogTag;
// "wslogin"
public void getData(String funcao, String username, String password)
{


    String url = "http://www.xxxxxxxxx.xxx/index.php/site/" + funcao + "?u="+username+"&p="+ password;
    Log.e(mLogTag, "getting car data\n" + url);
    DownloadJsonFile downloadCarData = new DownloadJsonFile();
    downloadCarData.execute(url);
}

// Método para prevenir Duplo click
public static void disableButton(final View v)
{
    try
    {
        v.setEnabled(false);
        v.setAlpha((float) 0.5);
        v.postDelayed(new Runnable()
        {
            @Override
            public void run()
            {
                try
                {
                    v.setEnabled(true);
                    v.setAlpha((float) 1.0);
                } catch (Exception e)
                {
                    Log.d("disableButton","Exception while un hiding the view: " + e.getMessage());
                }
            }
        }, 1000);
    } catch (Exception e)
    {
        Log.d("disableButton","Exception while hiding the view : " + e.getMessage());
    }
}

private void updateCarDataset(String json) throws JSONException
{
    JSONArray array = new JSONArray(json);

    for (int i = 0; i < array.length(); i++)
    {
        JSONObject object = array.getJSONObject(i);
        Integer carID = object.getInt("viaturaID");
        String lPlate = object.getString("matricula");
        Integer companyID = object.getInt("empresaID");
        Integer modelID = object.getInt("modeloID");
        Integer driverID = object.getInt("condutorID");
        Integer departmentID = object.getInt("departamentoID");
        Integer fuelID = object.getInt("combustivelID");
        Integer image = object.getInt("imagem");
        Integer idTypeVehicle = object.getInt("idtipoviatura");
        Long locationID = object.getLong("localizacaoID");
        Double latit = object.getDouble("lat");
        Double longt = object.getDouble("lon");
        String dateTime = object.getString("datahora");
        Double speed = object.getDouble("speed");
        Integer brandID = object.getInt("marcaID");
        String model = object.getString("modelo");
        String brand = object.getString("marca");
        String company = object.getString("empresa");
        Long nif = object.getLong("NIF");
        String address = object.getString("morada");
        String place = object.getString("local");
        String cp = object.getString("cp");
        String phone = object.getString("telefone");
        String email = object.getString("mail");
        String responsable = object.getString("responsavel");
        String expirationLicense = object.getString("validadeLicenca");
        Integer litersWarningDepot = object.getInt("LitrosAvisoDeposito");
        Integer kmsReminder = object.getInt("KmsLembrete");
        Integer daysReminder = object.getInt("diasLembrete");
        Integer outsiderNr = object.getInt("nrexterno");
        String name = object.getString("nome");
        String fuel = object.getString("combustivel");
        Double lastPrice = object.getDouble("ultimoPreco");


        carsDataset.add(new CarDataset(carID,lPlate, companyID, modelID, driverID, departmentID, fuelID, image, locationID, idTypeVehicle, latit, longt, dateTime, speed, brandID, model, brand, company, nif, address, place, cp, phone, email, responsable, expirationLicense, litersWarningDepot, kmsReminder, daysReminder, outsiderNr, name, fuel, lastPrice));
    }
    Log.d("my Tag", carsDataset.get(1).licencePlate);
    if (ValidateCredentials(carsDataset) == true)
    {
        userEntry = new User(user, pass);
        Intent login = new Intent();
        login.putExtra("user", userEntry);

        login.setClass(MainActivity.this, Menu.class);
        startActivity(login); // Começa a nova Actividade
        MainActivity.this.finish(); // Termina esta atividade
    }
    else
    {
        Toast.makeText(MainActivity.this, "Credencias Erradas. Tente de Novo", Toast.LENGTH_LONG).show();
    }
}

public boolean ValidateCredentials(ArrayList<CarDataset> testArray)
{
    if (testArray.isEmpty())
    {
        return false;
    }
    else
    {
        return true;
    }

}

public class DownloadJsonFile extends AsyncTask<String, Void, String> {
    @Override

    protected String doInBackground(String... params)
    {
        try
        {
            URL url = new URL(params[0]);

            // Open a stream from the URL
            InputStream stream = new URL(params[0]).openStream();

            String line;
            StringBuilder result = new StringBuilder();
            BufferedReader reader = new BufferedReader(new InputStreamReader(stream));

            while ((line = reader.readLine()) != null)
            {
                result.append(line);
                Log.e(mLogTag, "reading ...");
            }

            // Close the stream
            reader.close();
            stream.close();

            return result.toString();// + params[1];
        }
        catch (IOException e)
        {
            Log.e(mLogTag, "download data could not be read");
        }
        return null;
    }

    @Override
    protected void onPostExecute(String jsonObject)
    {
        if (jsonObject != null)
        {
            try
            {
                Log.e(mLogTag, "data received ->" + jsonObject);

                if (!jsonObject.contains("noDataAvailable"))
                {
                    try
                    {
                        updateCarDataset(jsonObject);
                    } catch (JSONException e)
                    {
                        e.printStackTrace();
                    }
                }
                else
                {
                    Log.e(mLogTag, "heello");
                }
            }
            catch (Exception ex)
            {
                ex.printStackTrace();
            }
        }
    }
}

}

这是我的第二个 Activity:

public class SelectCarToTrack extends AppCompatActivity
{
private String mLogTag;
private User userEntry = null;
RecyclerView recyclerView;
ArrayList<String> matriculas = new ArrayList<>();;
ArrayList<CarDataset> carros = new ArrayList<>();;
CarDataset selecionado = null;

private String user;
private String pass;


// Necessário para o RecyclerView
@Override
protected void onSaveInstanceState(Bundle outState)
{
    super.onSaveInstanceState(outState);
    ((CarExpandableAdapter)recyclerView.getAdapter()).onSaveInstanceState(outState);
}

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

    String carFuncao = "wslogin";

    Intent i = getIntent();
    userEntry = (User) i.getExtras().getParcelable("user");
    user = userEntry.getUsername();
    pass = userEntry.getPassword();

    String Url = "http://www.xxxxxxxx.xxx/index.php/site/"+ carFuncao + "?u=" + user + "&p=" + pass;
    Log.d("myTag", user);
    Log.d("myTag", pass);


    getData(carFuncao, user, pass);


    obtainLicensePlates(carros);

    Log.d("myTag", carros.get(0).licencePlate); // ERROR COMING THROUGH HERE!
    recyclerView = (RecyclerView)findViewById(R.id.rv_listcars);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    CarExpandableAdapter adapter = new CarExpandableAdapter(this,initData(matriculas));
    adapter.setParentClickableViewAnimationDefaultDuration();
    adapter.setParentAndIconExpandOnClick(true);

    recyclerView.setAdapter(adapter);
    recyclerView.addOnItemTouchListener(new RecyclerItemClickListener(SelectCarToTrack.this, recyclerView, new RecyclerItemClickListener.OnItemClickListener()
    {
        @Override
        public void onItemClick(View view, int position)
        {
            selecionado = carros.get(position);
            Intent geolocalizarSpecific = new Intent();
            geolocalizarSpecific.putExtra("select", selecionado);
            geolocalizarSpecific.setClass(SelectCarToTrack.this, Geolocalizcao.class);
            startActivity(geolocalizarSpecific);
        }

        @Override
        public void onItemLongCLick(View view, int position)
        {
        }
    }));
}

private void obtainLicensePlates(ArrayList<CarDataset> cars)
{
    if(cars != null)
    {
        for(int i=0; i < carros.size(); i++)
        {
            String temp = "";
            temp = carros.get(i).licencePlate;
            matriculas.add(i,temp);
        }
    }
    else
    {
        Toast.makeText(SelectCarToTrack.this, "Não foram recebidos dados", Toast.LENGTH_LONG).show();
    }
}

// O que acontece quando clico o botão para voltar para atrás
@Override
public void onBackPressed() {
    Intent goBack = new Intent();
    goBack.putExtra("user", userEntry );
    goBack.setClass(SelectCarToTrack.this, Menu.class);
    startActivity(goBack);
    SelectCarToTrack.this.finish();
}

private List<ParentObject> initData(ArrayList<String> licensePlates)
{
    CarCreator carCreator = CarCreator.get(this, licensePlates);
    List<CarParent> cars = carCreator.getAll();
    List<ParentObject> parentObject = new ArrayList<>();
    for(CarParent car:cars)
    {
        List<Object> childList = new ArrayList<>();
        childList.add(new CarChild("Track your vehicle","See Details"));
        car.setChildObjectList(childList);
        parentObject.add(car);
    }
    return parentObject;
}

public void getData(String funcao, String username, String password)
{
    // funcao = wslogin

    String Url = "http://www.xxxxx.xxx/index.php/site/"+ funcao + "?u=" + username + "&p=" + password;
    Log.e(mLogTag, "getting car data\n" + Url);
    DownloadJsonFile downloadCarData = new DownloadJsonFile();
    downloadCarData.execute(Url);
}

private void updateCarDataset(String json) throws JSONException
{
    JSONArray array = new JSONArray(json);

    for (int i = 0; i < array.length(); i++)
    {
        JSONObject object = array.getJSONObject(i);
        Integer carID = object.getInt("viaturaID");
        String lPlate = object.getString("matricula");
        Integer companyID = object.getInt("empresaID");
        Integer modelID = object.getInt("modeloID");
        Integer driverID = object.getInt("condutorID");
        Integer departmentID = object.getInt("departamentoID");
        Integer fuelID = object.getInt("combustivelID");
        Integer image = object.getInt("imagem");
        Integer idTypeVehicle = object.getInt("idtipoviatura");
        Long locationID = object.getLong("localizacaoID");
        Double latit = object.getDouble("lat");
        Double longt = object.getDouble("lon");
        String dateTime = object.getString("datahora");
        Double speed = object.getDouble("speed");
        Integer brandID = object.getInt("marcaID");
        String model = object.getString("modelo");
        String brand = object.getString("marca");
        String company = object.getString("empresa");
        Long nif = object.getLong("NIF");
        String address = object.getString("morada");
        String place = object.getString("local");
        String cp = object.getString("cp");
        String phone = object.getString("telefone");
        String email = object.getString("mail");
        String responsable = object.getString("responsavel");
        String expirationLicense = object.getString("validadeLicenca");
        Integer litersWarningDepot = object.getInt("LitrosAvisoDeposito");
        Integer kmsReminder = object.getInt("KmsLembrete");
        Integer daysReminder = object.getInt("diasLembrete");
        Integer outsiderNr = object.getInt("nrexterno");
        String name = object.getString("nome");
        String fuel = object.getString("combustivel");
        Double lastPrice = object.getDouble("ultimoPreco");


        carros.add(new CarDataset(carID, lPlate, companyID, modelID, driverID, departmentID, fuelID, image, locationID, idTypeVehicle, latit, longt, dateTime, speed, brandID, model, brand, company, nif, address, place, cp, phone, email, responsable, expirationLicense, litersWarningDepot, kmsReminder, daysReminder, outsiderNr, name, fuel, lastPrice));
    }
}


public class DownloadJsonFile extends AsyncTask<String, Void, String> {
    @Override

    protected String doInBackground(String... params)
    {
        try
        {
            URL url = new URL(params[0]);

            // Open a stream from the URL
            InputStream stream = new URL(params[0]).openStream();

            String line;
            StringBuilder result = new StringBuilder();
            BufferedReader reader = new BufferedReader(new InputStreamReader(stream));

            while ((line = reader.readLine()) != null)
            {
                result.append(line);
                Log.e(mLogTag, "reading ...");
            }

            // Close the stream
            reader.close();
            stream.close();

            return result.toString();// + params[1];
        }
        catch (IOException e)
        {
            Log.e(mLogTag, "download data could not be read");
        }
        return null;
    }

    @Override
    protected void onPostExecute(String jsonObject)
    {
        if (jsonObject != null)
        {
            try
            {
                Log.e(mLogTag, "data received ->" + jsonObject);

                if (!jsonObject.contains("noDataAvailable"))
                {
                    try
                    {
                        updateCarDataset(jsonObject);
                    } catch (JSONException e)
                    {
                        e.printStackTrace();
                    }
                }
                else
                {
                    Log.e(mLogTag, "heello");
                }
            }
            catch (Exception ex)
            {
                ex.printStackTrace();
            }
        }
    }
}

}

Logcat:

                                                       [ 11-18 17:29:58.579 10015:10015 E/         ]
                                                       getting car data
                                                       http://www.gescar3w.com/index.php/site/wslogin?u=xxxxxxx@xxxxx.xxx&p=xxxxxxx
11-18 17:29:58.580 10015-10015/g3w.gescarcopytest D/AndroidRuntime: Shutting down VM
11-18 17:29:58.582 10015-10015/g3w.gescarcopytest E/AndroidRuntime: FATAL EXCEPTION: main
                                                                Process: g3w.gescarcopytest, PID: 10015
                                                                java.lang.RuntimeException: Unable to start activity ComponentInfo{g3w.gescarcopytest/g3w.gescarcopytest.SelectCarToTrack}: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                                    at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:105)
                                                                    at android.os.Looper.loop(Looper.java:164)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6541)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                                                 Caused by: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
                                                                    at java.util.ArrayList.get(ArrayList.java:437)
                                                                    at g3w.gescarcopytest.SelectCarToTrack.onCreate(SelectCarToTrack.java:79)
                                                                    at android.app.Activity.performCreate(Activity.java:6975)
                                                                    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
                                                                    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
                                                                    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
                                                                    at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
                                                                    at android.os.Handler.dispatchMessage(Handler.java:105) 
                                                                    at android.os.Looper.loop(Looper.java:164) 
                                                                    at android.app.ActivityThread.main(ActivityThread.java:6541) 
                                                                    at java.lang.reflect.Method.invoke(Native Method) 
                                                                    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 
11-18 17:29:58.592 10015-10020/g3w.gescarcopytest I/zygote: Do partial code cache collection, code=118KB, data=102KB
11-18 17:29:58.592 10015-10020/g3w.gescarcopytest I/zygote: After code cache collection, code=118KB, data=102KB
11-18 17:29:58.592 10015-10020/g3w.gescarcopytest I/zygote: Increasing code cache capacity to 512KB
11-18 17:29:58.592 10015-10020/g3w.gescarcopytest I/zygote: JIT allocated 56KB for compiled code of void android.view.View.<init>(android.content.Context, android.util.AttributeSet, int, int)

我正在获取用户的信息，没问题...代码几乎相同，除了它有回收站视图的部分和所有其他部分。但是我看不出哪里错了...

Answer 1

感谢 Ben P. 所说的，我设法弄清楚了。 AsyncTask 需要一点时间来读取数据，大约需要 2/3 秒。因此，立即询问信息是行不通的，而且会导致崩溃。

我必须在第二次 activity 中调用 getData 后获取所有内容，并在更新 ArrayList 后放置它。现在看起来像这样：

private void updateCarDataset(String json) throws JSONException {
    JSONArray array = new JSONArray(json);

    for (int i = 0; i < array.length(); i++) {
        JSONObject object = array.getJSONObject(i);
        Integer carID = object.getInt("viaturaID");
        String lPlate = object.getString("matricula");
        Integer companyID = object.getInt("empresaID");
        Integer modelID = object.getInt("modeloID");
        Integer driverID = object.getInt("condutorID");
        Integer departmentID = object.getInt("departamentoID");
        Integer fuelID = object.getInt("combustivelID");
        Integer image = object.getInt("imagem");
        Integer idTypeVehicle = object.getInt("idtipoviatura");
        Long locationID = object.getLong("localizacaoID");
        Double latit = object.getDouble("lat");
        Double longt = object.getDouble("lon");
        String dateTime = object.getString("datahora");
        Double speed = object.getDouble("speed");
        Integer brandID = object.getInt("marcaID");
        String model = object.getString("modelo");
        String brand = object.getString("marca");
        String company = object.getString("empresa");
        Long nif = object.getLong("NIF");
        String address = object.getString("morada");
        String place = object.getString("local");
        String cp = object.getString("cp");
        String phone = object.getString("telefone");
        String email = object.getString("mail");
        String responsable = object.getString("responsavel");
        String expirationLicense = object.getString("validadeLicenca");
        Integer litersWarningDepot = object.getInt("LitrosAvisoDeposito");
        Integer kmsReminder = object.getInt("KmsLembrete");
        Integer daysReminder = object.getInt("diasLembrete");
        Integer outsiderNr = object.getInt("nrexterno");
        String name = object.getString("nome");
        String fuel = object.getString("combustivel");
        Double lastPrice = object.getDouble("ultimoPreco");


        carros.add(new CarDataset(carID, lPlate, companyID, modelID, driverID, departmentID, fuelID, image, locationID, idTypeVehicle, latit, longt, dateTime, speed, brandID, model, brand, company, nif, address, place, cp, phone, email, responsable, expirationLicense, litersWarningDepot, kmsReminder, daysReminder, outsiderNr, name, fuel, lastPrice));
    }

    obtainLicensePlates(carros);

    recyclerView = (RecyclerView) findViewById(R.id.rv_listcars);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    CarExpandableAdapter adapter = new CarExpandableAdapter(this, initData(matriculas));
    adapter.setParentClickableViewAnimationDefaultDuration();
    adapter.setParentAndIconExpandOnClick(true);

    recyclerView.setAdapter(adapter);
    recyclerView.addOnItemTouchListener(new RecyclerItemClickListener(SelectCarToTrack.this, recyclerView, new RecyclerItemClickListener.OnItemClickListener() {

        @Override
        public void onItemClick(View view, int position) {
            selecionado = carros.get(position);
            Intent geolocalizarSpecific = new Intent();
            geolocalizarSpecific.putExtra("select", selecionado);
            geolocalizarSpecific.setClass(SelectCarToTrack.this, Geolocalizcao.class);
            startActivity(geolocalizarSpecific);
        }

        @Override
        public void onItemLongCLick(View view, int position) {
        }
    }));
}

无法解析 android 工作室中的 json，它在一个 activity 而不是另一个工作室中工作

Trouble parsing a json in android studio that works in one activity and not the other

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null-pointer