如何将 JSON 数据从 Activity 传递到 Fragment

Question

When I passing JSON data from Activity to Fragment, it doesn't work. I want to get two data(Name & CarRemaining) and show in RecyclerView. How can I improve my code? Thanks!

public class Search extends MainActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.layout_search);
        ...
        String url = "API...";
        new ParkTask().execute(url);
    }

    class ParkTask extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {
        StringBuilder json = new StringBuilder();

        try {
            URL url = new URL(params[0]);
            Log.d(TAG, "AsyncTask doInBackground: " + params[0]);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            InputStream is = connection.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            String line = br.readLine();
            while (line != null) {
                json.append(line);
                line = br.readLine();
            }

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

        return json.toString();
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);

        JSONObject jonObject = null;
        List<Park> parks = new ArrayList<>();
        Bundle bundle = new Bundle();

        try {
            jonObject = new JSONObject(result);
            JSONArray recordArray = jonObject.getJSONArray("ParkingInfoList");

            for (int i = 0; i < recordArray.length(); i++) {
                JSONObject object = recordArray.getJSONObject(i);
                String name = object.getString("Name");
                String tel=object.getString("Tel");
                String address = object.getString("Address");
                String carTotal = object.getString("CarTotal");
                String carRemaining = object.getString("CarRemaining");
                String serviceTime = object.getString("ServiceTime");
                String chargeInfo = object.getString("ChargeInfo");
                String parkingInfo = object.getString("ParkingInfo");
                String lat = object.getString("Lat");
                String lng = object.getString("Lng");
                parks.add(new Park(name, address, tel, carTotal, carRemaining,
                        serviceTime, chargeInfo, parkingInfo, lat, lng));
                Log.d(TAG, "AsyncTask onPostExecute: " +
                        name + tel + address + carTotal +
                        carRemaining + serviceTime + chargeInfo +
                        parkingInfo + lat + lng );
                bundle.putString("key",object.toString());
            }
            bundle.putString("key",jonObject.toString());
            DesignatedFragment designatedFragment = new DesignatedFragment();
            designatedFragment.setArguments(bundle);
            getSupportFragmentManager().beginTransaction().replace(R.id.recycler,designatedFragment).commit();


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

I try to use Bundle to passing JSONdata. But I got NPE in this line.

String jsonString=bundle.getString("key");

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.BaseBundle.getString(java.lang.String)' on a null object reference

This is my fragment.

public class DesignatedFragment extends Fragment{
    List<Park> parks = new ArrayList<>();
.
.
.
@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        Bundle bundle=getArguments();
        String jsonString=bundle.getString("key");
        JSONObject object;
        try {
            object=new JSONObject(jsonString);
            recycler.setAdapter(new ParkAdapter(parks));
        }catch (JSONException e){
            e.printStackTrace();
        }

        return inflater.inflate(R.layout.fragment_designated, container, false);
    }
}

And I use RecyclerView to show data.

fragment_designated.xml

<androidx.constraintlayout.widget.ConstraintLayout 
...
    tools:context=".DesignatedFragment">

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        tools:ignore="MissingConstraints" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="49dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>

another one row.xml

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">


    <TextView
        android:id="@+id/parkSpace"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="15dp"
        android:layout_marginLeft="15dp"
        android:layout_marginTop="17dp"
        android:textColor="#464646"
        android:textSize="24sp"
        android:textStyle="normal"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="MissingConstraints"
        tools:text="Car Remaining" />

    <TextView
        android:id="@+id/parkName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="15dp"
        android:layout_marginLeft="15dp"
        android:layout_marginBottom="17dp"
        android:textColor="#464646"
        android:textSize="18sp"
        android:textStyle="normal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        tools:ignore="MissingConstraints"
        tools:text="ParkName" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="45dp"
        android:layout_marginEnd="11dp"
        android:layout_marginRight="11dp"
        android:layout_marginBottom="44dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/kit_right"
        tools:ignore="ContentDescription" />

</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

Extend your class Park to Serializeable or Parceable, Then you can pass object in bundle to fragment.

https://developer.android.com/reference/android/os/Parcelable

other solution is to convert your Object class to string and revert back to Object class.You can use Gson() librabry.