Question

尝试访问Android中doInBackground（）返回的对象时遇到了一些问题。当我的按钮onClick时，它将执行 GetEventDetailAsyncTask 类中的doInBackground（）：

viewDtlEventBtn.setOnClickListener(new OnClickListener(){
        public void onClick(View v){
            //eventModel.setEventID(String.valueOf(eventIDTV.getText()));
            new GetEventDetailAsyncTask(new GetEventDetailAsyncTask.OnRoutineFinished() {
                public void onFinish() {
                    // Passing whole object with value into another activity
                    Intent eventDtlIntent = new Intent(context, EventDetailMain.class);
                    eventDtlIntent.putExtra("eventObj", eventModel);
                    eventDtlIntent.putExtra("eventCommentObj", eventCommentModel);
                    context.startActivity(eventDtlIntent);
                }
            }).execute(String.valueOf(eventIDTV.getText()));
        }
    });

然后在我的 GetEventDetailAsyncTask 类中，它将执行返回EventComment对象的 EventController 类中的方法：

public class GetEventDetailAsyncTask extends AsyncTask<String, Integer, EventComment> {
EventController eventCtrl = new EventController();
Context context;
EventComment comment = new EventComment();

public interface OnRoutineFinished { // interface
    void onFinish();
}

private OnRoutineFinished mCallbacks;

public GetEventDetailAsyncTask(OnRoutineFinished callback) { // constructor with
                                                    // interface
    mCallbacks = callback;
}

public GetEventDetailAsyncTask() {
} // empty constructor to maintain compatibility

public GetEventDetailAsyncTask(Context context){
    this.context = context;
}

@Override
protected Double doInBackground(String... params) {

    try {
        //eventCtrl.getEventDetailByID(params[0]);
        eventCtrl.getEventCommentByID(params[0]);
    } catch (JSONException e) {
        e.printStackTrace();
    }

    return null;
}

protected void onPostExecute(EventComment result) {
    comment = result;
    if (mCallbacks != null)
        mCallbacks.onFinish(); // call interface on finish
}

protected void onProgressUpdate(Integer... progress) {
}

}

EventController类

public EventComment getEventCommentByID(String eventID) throws JSONException {
    EventComment eventCommentModel = new EventComment();
    String page;
    JSONArray jsonArray;
    try {
        HttpClient client = new DefaultHttpClient();
        HttpGet request = new HttpGet(ENeighbourhoodActivity.URL
                + "/EventServlet?action=GetCommentById&eventID=" + eventID
                + "");
        HttpResponse response = client.execute(request);
        HttpEntity entity = response.getEntity();
        String responseString = EntityUtils.toString(entity, "UTF-8");
        page = "{\'EventComment\':" + responseString + "}";
        try {
            JSONObject jsonObject = new JSONObject(page);
            jsonArray = jsonObject.getJSONArray("EventComment");
            int length = jsonArray.length();
            for (int i = 0; i < length; i++) {
                JSONObject attribute = jsonArray.getJSONObject(i);
                String commentBy = attribute.getString("commentBy");
                String commentDate = attribute.getString("commentDate");
                String commentTime = attribute.getString("commentTime");
                String commentDesc = attribute.getString("commentDesc");
                eventCommentModel.setCommentBy(commentBy);
                eventCommentModel.setCommentDate(commentDate);
                eventCommentModel.setCommentTime(commentTime);
                eventCommentModel.setCommentDesc(commentDesc);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    return eventCommentModel;
}

然而，当我的按钮是onClick并将eventComment对象作为参数传递给 EventChat 类时，它为null并且在尝试访问对象本身时我得到NullPointerException。

有什么想法吗？提前谢谢。

Answer 1

这段代码有些可疑：

try {
    eventCtrl.getEventDetailByID(params[0]);
    eventCtrl.getEventCommentByID(params[0]);
} catch (JSONException e) {
    e.printStackTrace();
}

return null;

仔细看看，你打电话给eventCtrl.getEventDetailByID(params[0]);，但不要保存它返回的内容。

您需要创建EventComment的实例并使用它：

myEvenComment = eventCtrl.getEventCommentByID(params[0]);

访问从AsyncTask NullPointerException返回的Object

1 个答案: