Question

我正在尝试制作ListView。但是，发生错误，

“尝试在空对象引用上调用虚方法'void android.widget.ListView.setAdapter（android.widget.ListAdapter）'”。

这是BookedCourseListAdpater的代码

public class BookedCourseListAdapter extends BaseAdapter{

private Context context;
private List<BookedCourse> BookedList;
private Activity parentActivity;







public BookedCourseListAdapter(Context context, List<BookedCourse> BookedCourseList, Activity parentActivity){
    this.context = context;
    this.BookedList = BookedCourseList;
    this.parentActivity = parentActivity;



}




@Override
public int getCount() {
    return BookedList.size();
}

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

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





@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    @SuppressLint("ViewHolder") View v = View.inflate(context, result, null);
    //View v = View.inflate(context,R.layout.result, null);
    final TextView BookedCourseTeacher = (TextView) v.findViewById(R.id.BookedCourseTeacher);
    final TextView BookedCourseDay = (TextView) v.findViewById(R.id.BookedCourseDay);
    final TextView BookedCourseTime = (TextView) v.findViewById(R.id.BookedCourseTime);



    BookedCourseTeacher.setText(BookedList.get(position).getBookedCourseTeacher());
    BookedCourseDay.setText(BookedList.get(position).getBookedCourseDay());
    BookedCourseTime.setText(BookedList.get(position).getBookedCourseTime());


    v.setTag(BookedList.get(position).getBookedCourseID());

    Button cancelButton = (Button) v.findViewById(R.id.cancelButton);
    cancelButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Response.Listener<String> responseListener = new Response.Listener<String>(){
                public void onResponse(String response){
                    try{
                        JSONObject jsonResponse = new JSONObject(response);
                        boolean success = jsonResponse.getBoolean("success");
                        if(success){
                            BookedList.remove(position);

                            notifyDataSetChanged();

                        }

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


                }

            };
            CancelRequest cancelRequest = new CancelRequest(BookedList.get(position).getBookedCourseID() +" ",BookedList.get(position).getBookedCourseBranch().toString(), responseListener);
            RequestQueue queue = Volley.newRequestQueue(parentActivity);
            queue.add(cancelRequest);


        }
    });
    return v;



}


 }

这是BookedCourse的代码

public class BookedCourse {

String BookedCourseTeacher;
String BookedCourseDay;
String BookedCourseTime;
int BookedCourseID;
String BookingUserID;
String BookedCourseBranch;

public String getBookedCourseBranch() {
    return BookedCourseBranch;
}

public void setBookedCourseBranch(String bookedCourseBranch) {
    BookedCourseBranch = bookedCourseBranch;
}

public String getBookingUserID() {
    return BookingUserID;
}

public void setBookingUserID(String bookingUserID) {
    BookingUserID = bookingUserID;
}

public int getBookedCourseID() {
    return BookedCourseID;
}

public void setBookedCourseID(int bookedCourseID) {
    BookedCourseID = bookedCourseID;
}



public BookedCourse(String bookingUserID, String bookedCourseTeacher, String bookedCourseDay, String bookedCourseTime, int bookedCourseID, String bookedCourseBranch) {
    this.BookingUserID = bookingUserID;
    this.BookedCourseTeacher = bookedCourseTeacher;
    this.BookedCourseDay = bookedCourseDay;
    this.BookedCourseTime = bookedCourseTime;
    this.BookedCourseID = bookedCourseID;
    this.BookedCourseBranch = bookedCourseBranch;
}

public String getBookedCourseTeacher() {
    return BookedCourseTeacher;
}

public void setBookedCourseTeacher(String bookedCourseTeacher) {
    BookedCourseTeacher = bookedCourseTeacher;
}

public String getBookedCourseDay() {
    return BookedCourseDay;
}

public void setBookedCourseDay(String bookedCourseDay) {
    BookedCourseDay = bookedCourseDay;
}

public String getBookedCourseTime() {
    return BookedCourseTime;
}

public void setBookedCourseTime(String bookedCourseTime) {
    BookedCourseTime = bookedCourseTime;
}
}

以下是从MySQL解析数据的部分

private int parseData(){
    try {
        JSONArray ja = new JSONArray(jsonData);
        JSONObject jo = null;


        BookedList.clear();
        BookedCourse bookedCourse = null;
        for(int i = 0; i <ja.length();i++)
        {
            jo = ja.getJSONObject(i);
            String bookinguserID = jo.getString("userID");
            int id = jo.getInt("courseID");
            String courseBranch = jo.getString("courseBranch");
            String bookedCourseTeacher = jo.getString("courseTeacher");
            String bookedCourseDay = jo.getString("courseDay");
            String bookedCourseTime = jo.getString("courseTime");

           if(bookinguserID.equals(userID))
            {
               bookedCourse = new BookedCourse(bookinguserID, bookedCourseTeacher, bookedCourseDay, bookedCourseTime, id, courseBranch);
               BookedList.add(bookedCourse);
            }




            }
        }


        return 1;

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

    return  0;

    }

这是setAdapter到listview的部分

public class Result extends AppCompatActivity {

private ListView resultlist;
private BookedCourseListAdapter adapter;


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

    resultlist = (ListView) findViewById(R.id.userListView);
    adapter = new BookedCourseListAdapter(getApplicationContext(),BookedList, this);
    resultlist.setAdapter(adapter);
}
}

我不认为BookedList为null。那为什么在空对象上调用setAdapter？

Answer 1

我在任何地方都看不到parseData()的来电。这是我的猜测，但是您可能没有将任何对象分配到列表中吗？

最好将此处的整个活动发布在此处。

'null对象引用上的'ListView.setAdapter（android.widget.ListAdapter）'

1 个答案: