Question

我是android新手我已经应用了所有解决方案。但问题没有解决。我为asyncTask，adapter，Model制作了单独的类 activity oncreate调用asyncTask类。在asyncTask适配器中调用和listview被调用。善意的帮助。提前致谢

我的活动是

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_course_outlines);
        CourseOutlinesTask task = new CourseOutlinesTask(CourseOutlinesActivity.this);     task.execute("http://mantis.vu.edu.pk/bridging_the_gap/public/viewCourseOutlines");

asyncTASK CLASS是

public class CourseOutlinesTask extends AsyncTask<String, String, String> {
    ProgressDialog dialog;
    Activity context;
    private ArrayList<CourseModel> postList = new ArrayList<CourseModel>();
    private ListView listView;
    TrainerCourseAdapter adapter;


    public CourseOutlinesTask(Activity context) {

        context = this.context;
    }


    @Override
    protected void onPreExecute() {

    }

    @Override
    protected String doInBackground(String... params) {
        HttpURLConnection connection = null;
        BufferedReader reader = null;
        try {
            URL url = new URL(params[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();
            InputStream stream = connection.getInputStream();
            reader = new BufferedReader(new InputStreamReader(stream));
            StringBuffer buffer = new StringBuffer();
            String line = "";
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }
            return buffer.toString();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (connection != null)
                connection.disconnect();
            try {
                if (reader != null)
                    reader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override

    protected void onPostExecute(String result) {
                super.onPostExecute(result);
        //close process dialog
        if (this.dialog != null) {
            this.dialog.dismiss();
        }
        //parse json
        try {
            JSONObject jsonParse = new JSONObject(result);
            JSONArray query = jsonParse.getJSONArray("courses");
            for (int i = 0; i < query.length(); i++) {
                try {
                    JSONObject jsonParser = query.getJSONObject(i);

                    CourseModel post = new CourseModel();
                    post.setId(jsonParser.getInt("id"));
                    post.setTitle(jsonParser.getString("title"));
                    post.setStatus(jsonParser.getString("status"));
                    post.setDescription(jsonParser.getString("description"));
                    System.out.println(post.getStatus()+"asdadasdad");
                    System.out.println(post);
                    postList.add(post);
                    TrainerCourseAdapter adapter = new TrainerCourseAdapter(context,postList);
                    System.out.println("ttttttttttttttttttttt");
                    listView = (ListView) context.findViewById(R.id.course_listView);

                    listView.setAdapter(new TrainerCourseAdapter(context,postList));
        }catch (Exception e) {
                    System.out.println(e);
        }
            // Parsing json

                    post.setDescription(obj.getString("description"));

            }
        } else {
            MyAppUtil.getToast(getApplicationContext(), message);
        }*/
    }
    } catch (JSONException e) {
            e.printStackTrace();
        }
    }
}

我的适配器类是

public class TrainerCourseAdapter extends BaseAdapter {
private  List list;
    private Context context;
    private static LayoutInflater inflater = null;

    String [] cName;
    String [] cDetail;
    String [] created;
    String [] cStatus;
    ArrayList<CourseModel> itemList;
    Context mcontext;


    public TrainerCourseAdapter(Context context,List list) {
        System.out.println("aaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
        mcontext = context;
        itemList = (ArrayList<CourseModel>) this.list;
    }


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

    @Override
    public Object getItem(int i) {
        return i;
    }

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


    public void setItemList(ArrayList<CourseModel> itemList) {
        this.itemList = itemList;
    }

    public class Holder
    {
        TextView c_name;
        TextView c_detail;
        TextView c_date ;
        Button c_status;
    }

    @Override
    public View getView(final int i, View rowView, ViewGroup viewGroup) {
        Holder holder = new Holder();
        rowView = inflater.inflate(R.layout.row_courses_list, null);
        holder.c_name = (TextView) rowView.findViewById(R.id.txt_courseName);
        holder.c_detail = (TextView) rowView.findViewById(R.id.txt_courseDetail);
        holder.c_date = (TextView) rowView.findViewById(R.id.txt_courseDate);
        holder.c_status = (Button) rowView.findViewById(R.id.btn_courseStatus);

        final CourseModel data = itemList.get(i);
        holder.c_name.setText(data.getTitle());
        holder.c_detail.setText(data.getDescription());
        holder.c_status.setText(data.getStatus());
        holder.c_date.setText(data.getId());
        rowView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(context, "You Clicked "+ cName[i], Toast.LENGTH_LONG).show();
            }
        });
        return rowView;
    }
}

模型是

public class CourseModel {
    private int id;
    private String title;
    private String description;
    private String status;
//    private int totalCount;

//    private int limit;
//    private String offset;

    public CourseModel(){

    }

    /*Getter for Course Model*/
    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }

    public String getStatus() {
        return status;
    }
    /*Endo of Model Getter*/

    /*Setter for Model*/

    public void setId(int id) {
        this.id = id;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    /*End for Model Setters*/


}

当我运行应用列表时为空并且错误是

10-05 19:22:04.352 10503-10537/vu.bc110201891.btg I/OpenGLRenderer: Initialized EGL, version 1.4
10-05 19:22:04.478 10503-10537/vu.bc110201891.btg D/OpenGLRenderer: Enabling debug mode 0
10-05 19:22:04.541 10503-10537/vu.bc110201891.btg W/EGL_emulation: eglSurfaceAttrib not implemented
10-05 19:22:04.541 10503-10537/vu.bc110201891.btg W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xeb9943c0, error=EGL_SUCCESS
10-05 19:22:04.718 10503-10503/vu.bc110201891.btg I/Choreographer: Skipped 30 frames!  The application may be doing too much work on its main thread.
10-05 19:22:05.564 10503-10503/vu.bc110201891.btg I/System.out: Rejectasdadasdad
10-05 19:22:05.564 10503-10503/vu.bc110201891.btg I/System.out: vu.bc110201891.btg.Models.CourseModel@21937920
10-05 19:22:05.565 10503-10503/vu.bc110201891.btg I/System.out: aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
10-05 19:22:05.565 10503-10503/vu.bc110201891.btg I/System.out: ttttttttttttttttttttt
10-05 19:22:05.565 10503-10503/vu.bc110201891.btg I/System.out: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference

Answer 1

下面：

 context = this.context;

context对象为null。在构造函数中将其更改为：

this.context = context;

在null对象引用上出错android.view.View android.widget.ListView.findViewById（int）'

1 个答案: