试图取消进度对话框中的AsyncTask在android系统时的空指针异常 [英] Null Pointer exception when trying to cancel Progress Dialog in AsyncTask in android

问题描述

我得到一个空指针异常而异步任务取消进度对话框..this是我的code..I'm从RSS Conecction获取数据7天Week..I的要取消对话框，停止任务，如果用户pressed后退按钮。

  @覆盖
    在preExecute保护无效（）{
        的ShowDialog（DIALOG_PROGRESS）;
        台历挂历= NULL;
        开关（天）{
            案例SAT：
                日历= DateUtil.getSaturdayDate（）;
                打破;
            案例SUN：
                日历= DateUtil.getSundayDate（）;
                打破;
            案例MON：
                日历= DateUtil.getMondayDate（）;
                打破;
            案例TUE：
                日历= DateUtil.getTuesdayDate（）;
                打破;
            案例WED：
                日历= DateUtil.getWednesdayDate（）;
                打破;
            案例THU：
                日历= DateUtil.getThursdayDate（）;
                打破;
            案例五：
                日历= DateUtil.getFridayDate（）;
                打破;
            默认：
                打破;
        }        如果（日历！= NULL）{
            generatedLink = WeeklyScheduleBean.generatePath（DateUtil.getDay（日历），
                                                             DateUtil.getMonth（日历），
                                                             DateUtil.getYear（日历））;
        }其他{
            //取得今天的日程安排
            日历CURRENT_DAY = DateUtil.getCurrentTime（）;
            generatedLink = WeeklyScheduleBean.generatePath（DateUtil.getDay（CURRENT_DAY）
                                                             DateUtil.getMonth（CURRENT_DAY）
                                                             DateUtil.getYear（CURRENT_DAY））;
        }
    }        @覆盖
    保护布尔doInBackground（虚空...... PARAMS）{
        feedParser =新WeeklyScheduleParser（generatedLink）;
        名单=新的ArrayList＆LT; WeeklyScheduleBean＆GT;（）;
        尝试{
            清单= feedParser.parse（）;
        }赶上（例外五）{
            e.printStackTrace（）;
            返回false;
        }        如果（则为list.size（）大于0）
            返回true;
        其他
            返回false;
    }        @覆盖
    保护无效onPostExecute（布尔结果）{
        如果（progressDialog.isShowing（））{
        如果（结果）{
            weeklyScheduleScreen.removeDialog（DIALOG_PROGRESS）;
            适配器=新WeeklyAdapter（CXT，R.layout.time_text_list，R.id.title_text，清单）;
            lv.setAdapter（适配器）;
        }
        其他{
            DialogUtil.CreateDialog（，无法检索提要，假的，WeeklyScheduleScreen.this）;
            weeklyScheduleScreen.removeDialog（DIALOG_PROGRESS）;
        }
        }
    }
}
 

解决方案

试图改变的ShowDialog（DIALOG_PROGRESS）; 到 progressDialog.show（） ;

I'm Getting a Null Pointer Exception while canceling the Progress Dialog in Async Task ..this is my code..I'm Getting Data from an RSS Conecction for 7 days of Week..I want to cancel the Dialog and stop the task if the user pressed Back Button.

          @Override
    protected void onPreExecute() {
        showDialog(DIALOG_PROGRESS);
        Calendar calendar = null;
        switch (day) {
            case SAT:
                calendar = DateUtil.getSaturdayDate();
                break;
            case SUN:
                calendar = DateUtil.getSundayDate();
                break;
            case MON:
                calendar = DateUtil.getMondayDate();
                break;
            case TUE:
                calendar = DateUtil.getTuesdayDate();
                break;
            case WED:
                calendar = DateUtil.getWednesdayDate();
                break;
            case THU:
                calendar = DateUtil.getThursdayDate();
                break;
            case FRI:
                calendar = DateUtil.getFridayDate();
                break;
            default:
                break;
        }

        if(calendar != null) {
            generatedLink = WeeklyScheduleBean.generatePath( DateUtil.getDay(calendar),
                                                             DateUtil.getMonth(calendar),
                                                             DateUtil.getYear(calendar) );
        } else {
            // get the schedule of today
            Calendar current_day = DateUtil.getCurrentTime();
            generatedLink = WeeklyScheduleBean.generatePath( DateUtil.getDay(current_day),
                                                             DateUtil.getMonth(current_day),
                                                             DateUtil.getYear(current_day) );
        }
    }

        @Override
    protected Boolean doInBackground(Void... params) {
        feedParser = new WeeklyScheduleParser(generatedLink);
        list = new ArrayList<WeeklyScheduleBean>();
        try {
            list = feedParser.parse();
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }           

        if(list.size() > 0)                             
            return true;
        else 
            return false;           
    }



        @Override
    protected void onPostExecute(Boolean result) {
        if(progressDialog.isShowing()){
        if(result) {
            weeklyScheduleScreen.removeDialog(DIALOG_PROGRESS);
            adapter = new WeeklyAdapter(cxt, R.layout.time_text_list, R.id.title_text, list);
            lv.setAdapter(adapter);
        } 
        else {
            DialogUtil.CreateDialog("", "Could not retreive the feeds",false,WeeklyScheduleScreen.this);
            weeklyScheduleScreen.removeDialog(DIALOG_PROGRESS);
        }
        }
    }
}

解决方案

try to change showDialog(DIALOG_PROGRESS); to progressDialog.show();

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