com.google.gson.internal.LinkedTreeMap cannot be cast

Question

I am using retrofit with GSON for the first time.It is Running Fluently with static data but it is showing the above error in the Case of the Dynamic Data.It is Showing error in the Adapter on setting the Text value

MainActivity

public class MainActivity extends AppCompatActivity {


    String Navigation_Url = "http://www.xxxxxxxx.com";
    ListView listView;
    ArrayList<ListPojo> listPojos = new ArrayList<>();
    ListRetrofitAndroid listRetrofitAndroid;


    ArrayList countries = new ArrayList();

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

        listView = (ListView) findViewById(R.id.listView);
        getRetrofitData();
    }


    void getRetrofitData() {
        Retrofit retrofit = new Retrofit.Builder().baseUrl(Navigation_Url).addConverterFactory(GsonConverterFactory.create()).build();
        CountryArrayAPI api = retrofit.create(CountryArrayAPI.class);
        Call<List> call = api.getCountries();


        call.enqueue(new Callback<List>() {

            @Override
            public void onResponse(Call<List> call, Response<List> response) {
                Gson gson = new Gson();
                try {
                    listPojos = (ArrayList) response.body();
                    System.out.println("the ArrayList is" + listPojos);


//                    ArrayList<ListPojo> merchantOfferModels = gson.fromJson(response, new TypeToken<ListPojo>() {}.getType());









                    listRetrofitAndroid = new ListRetrofitAndroid(getApplicationContext(), listPojos);
                    listView.setAdapter(listRetrofitAndroid);


                } catch (Exception e) {
                    Log.d("onResponse", "There is an error");
                    e.printStackTrace();
                }

            }

            @Override
            public void onFailure(Call<List> call, Throwable t) {
                Log.d("Failure", t.toString());
            }
        });

    }

}

ListRetrofitAndroid(Adapter)

public class ListRetrofitAndroid extends BaseAdapter {

    Context mContext;
    ArrayList<ListPojo> arrayList = new ArrayList<>();
    String TAG = "HomeTab_adapter";


    public ListRetrofitAndroid(Context context, ArrayList<ListPojo> listPojos) {
        super();
        this.mContext = context;
        this.arrayList = listPojos;

    }

    @Override
    public int getCount() {


        return arrayList.size();
    }

    @Override
    public Object getItem(int position) {
        return arrayList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        final Holder viewHolder;

        if (convertView == null) {
            LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//            convertView = inflater.inflate(R.layout.list, parent, false);
            convertView = inflater.inflate(R.layout.listview_item, parent, false);

            // well set up the ViewHolder
            //  viewHolder = new ClassScheduleStudentAdapter.Holder();
            viewHolder = new Holder();
            viewHolder.textName = convertView.findViewById(R.id.list_item_main);
            convertView.setTag(viewHolder);


        } else {

            viewHolder = (Holder) convertView.getTag();
        }

        viewHolder.textName.setText(arrayList.get(position).getTitle());


        return convertView;
    }

    class Holder {
        TextView textName;
    }


}

model(ListPojo)

public class ListPojo {

    String title;

    public ListPojo(String title) {
        this.title = title;
    }

    public String getTitle() {
        return title;
    }
}

interface

public interface CountryArrayAPI {
    @GET("/api/popular_destinations")
    public Call<List> getCountries();
}

JSON

[
    {
        "id": 1,
        "title": "Hiranya Varna Mahavihar",
        "location": "Kwalakhu Rd, Patan 44600, Nepal",
        "main_image": "images/popular_places/patan-durbar-square.jpg"
    },
    {
        "id": 2,
        "title": "Yasodhar Mahavihar-Bubahal",
        "location": "Jana Bahal Rd, Patan 44600, Nepal",
        "main_image": "images/popular_places/patan-durbar-square.jpg"
    },
    {
        "id": 3,
        "title": "Krishna Temple Sundhara",
        "location": "Tyagal - Lalitpur Rd, Patan 44600, Nepal",
        "main_image": "images/popular_places/Patan-2.jpg"
    },
    {
        "id": 4,
        "title": "Hiranya Varna Mahavihar",
        "location": "Kwalakhu Rd, Patan 44600, Nepal",
        "main_image": "images/popular_places/asd.jpg"
    }
]

StsckTrace

09-19 05:15:32.475 18949-18949/com.example.user_pc.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                   Process: com.example.user_pc.myapplication, PID: 18949
                                                                                   java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.example.user_pc.myapplication.pojo.ListPojo
                                                                                       at com.example.user_pc.myapplication.adpater.ListRetrofitAndroid.getView(ListRetrofitAndroid.java:71)
                                                                                       at android.widget.AbsListView.obtainView(AbsListView.java:2255)
                                                                                       at android.widget.ListView.measureHeightOfChildren(ListView.java:1263)
                                                                                       at android.widget.ListView.onMeasure(ListView.java:1175)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.support.constraint.ConstraintLayout.internalMeasureChildren(ConstraintLayout.java:934)
                                                                                       at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:973)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
                                                                                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
                                                                                       at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
                                                                                       at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
                                                                                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
                                                                                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
                                                                                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
                                                                                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
                                                                                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
                                                                                       at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
                                                                                       at android.view.View.measure(View.java:16497)
                                                                                       at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1912)
                                                                                       at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1109)
                                                                                       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1291)
                                                                                       at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)
                                                                                       at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5600)
                                                                                       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
                                                                                       at android.view.Choreographer.doCallbacks(Choreographer.java:574)
                                                                                       at android.view.Choreographer.doFrame(Choreographer.java:544)
                                                                                       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
                                                                                       at android.os.Handler.handleCallback(Handler.java:733)
                                                                                       at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                       at android.os.Looper.loop(Looper.java:136)
                                                                                       at android.app.ActivityThread.main(ActivityThread.java:5001)
                                                                                       at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                       at java.lang.reflect.Method.invoke(Method.java:515)
                                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
                                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
                                                                                       at dalvik.system.NativeStart.main(Native Method)

How can this issue be solved?

Answer 1

You are using ArrayList<ListPojo> so you need to make sure that the parsing should happen using right type List<ListPojo> instead of list which has no type

due to the missing type information , gson is returning a List of internally created objects LinkedTreeMap and since you are using raw types (should be a warning for unchecked cast)with declaration as concrete type which will create a issue when adapter actually expecting a PojoObject but internally it's something else. so solution

Never use raw-types anywhere possible

so do

public interface CountryArrayAPI {
    @GET("api/popular_destinations")
    public Call<List<ListPojo>> getCountries();
}

and also remove / before api and call will be like

call.enqueue(new Callback<List<ListPojo>>() {

            @Override
            public void onResponse(Call<List<ListPojo>> call, Response<List<ListPojo>> response) {
            listPojos = response.body();

and always code to interface so

List<ListPojo> listPojos = ...;

Answer 2

I currently exactly don't know how to handle the json using List. But you can use array like this:

public interface CountryArrayAPI {
    @GET("/api/popular_destinations")
    public Call<ListPojo[]> getCountries();
}