Question

我创建了一个AsyncTask，可以在我执行时从网站加载数据。目前我得到一个空指针异常，我认为是因为我试图过早填充UI所以我希望创建某种if语句，说明如果AsyncTask不完整显示加载图形以及何时填充数据。但是我不确定如何做到这一点有没有人知道我怎么能做到这一点或至少指出我正确的方向。

到目前为止，这是我的代码

public void checkPreferences(){

    SharedPreferences preferences = getSharedPreferences("prefs", Context.MODE_PRIVATE);
    ChosenMethod = preferences.getString("ChosenMethod", ChosenMethod);
    ChosenLeagueID = preferences.getString("ChosenLeagueId", ChosenLeagueID);
    ChosenTeamId = preferences.getString("ChosenTeamId", ChosenTeamId);

    Log.v("lc", "newsurl" + newsFeedURL);


    Log.v("myapp", "ChosenMethod Home = " + ChosenMethod);
    Log.v("myapp", "ChosenLeagueID Home = " + ChosenLeagueID);
    Log.v("myapp", "ChosenTeamID Home = " + ChosenTeamId);

    if (ChosenMethod.equals("Team")) {
        setContentView(R.layout.homeactteam2);
        newsAmount = 5;

    } else {
        newsAmount = 10;
        setContentView(R.layout.homeactteam);
    }

}


@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);

    //Check Preferences which sets UI

    checkPreferences();
   PostTask posttask;
   posttask = new PostTask();
   posttask.execute();

   FillData();


    Button backbtn = (Button) findViewById(R.id.backbtn);

    //Listening to button event
    backbtn.setOnClickListener(new View.OnClickListener() {

        public void onClick(View arg0) {
            //Starting a new Intent
            Intent previousScreen = new Intent(getApplicationContext(), ChooseTeamActivity.class);
            ChosenMethod = "null";
            SharedPreferences preferences = getSharedPreferences("prefs", Context.MODE_PRIVATE);
            SharedPreferences.Editor editor = preferences.edit();
            editor.putString("ChosenMethod", ChosenMethod);            
            editor.commit();
            previousScreen.putExtra("FullData", fulldata);
            startActivity(previousScreen);


        }
    });

//((PullToRefreshListView) getListView()).setOnRefreshListener(new OnRefreshListener() {
//   
//    public void onRefresh() {
//        // Do work to refresh the list here.
//        loadData();
//    }
//});
//


}



public void loadNewsFeed(){

     newsFeedRequest = "website/" + chosenLeagueId + "/news?timestamp=" + unixTimeStamp;
     newsFeedURL = "https://www.website.com" + newsFeedRequest; 

        String myhash = buildHmacSignature(apiKey, newsFeedURL);
        HttpClient client = new DefaultHttpClient();
        HttpPost post = new HttpPost(newsFeedURL);

        List<NameValuePair> pairs = new ArrayList<NameValuePair>();
        pairs.add(new BasicNameValuePair("requestToken", myhash));
        pairs.add(new BasicNameValuePair("apiUser", apiUser));

            try {
                post.setEntity (new UrlEncodedFormEntity(pairs));
                HttpResponse response = client.execute(post);
                BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
                String json = reader.readLine();
                fulldata = String.valueOf(json);
                Log.v("myApp","newsdata" + fulldata);

                newsList = new ArrayList<String>();
                newsList2 = new ArrayList<String>();
                newsList3 = new ArrayList<String>();
                imageList = new ArrayList<String>();


                JSONObject obj = new JSONObject(json);    
                JSONObject objData = obj.getJSONObject("data");
                JSONArray jArray = objData.getJSONArray("news");
                Log.v("lc","newsAmount= " + newsAmount);

                   for(int t = 0; t < newsAmount; t++){
                       JSONObject newsTitleDict = jArray.getJSONObject(t);
                       imageList.add(newsTitleDict.getString("image_small"));
                     newsList3.add(newsTitleDict.getString("title"));

                   }

                   for(int t = 0; t < 1; t++){
                       JSONObject newsTitleDict = jArray.getJSONObject(t);

                 newsList.add(newsTitleDict.getString("title"));
            //       newsList2.add(newsTitleDict.getString("title"));

                   }



    } catch (ClientProtocolException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }


}           


public void loadResultsFeed(){


    resultsFeedRequest = "website/" + chosenLeagueId + "/results?&team_id=" + ChosenTeamId + "&limit=31&timestamp=" + unixTimeStamp;
    resultsFeedURL = "https://www.website.com" + resultsFeedRequest;    

    String myhash = buildHmacSignature(apiKey, resultsFeedURL);

    HttpClient client = new DefaultHttpClient();
    HttpPost post = new HttpPost(resultsFeedURL);

    List<NameValuePair> pairs = new ArrayList<NameValuePair>();
    pairs.add(new BasicNameValuePair("requestToken", myhash));
    pairs.add(new BasicNameValuePair("apiUser", apiUser));

    try {
        post.setEntity (new UrlEncodedFormEntity(pairs));
        HttpResponse response = client.execute(post);
        BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
        String json = reader.readLine();
        fulldata = String.valueOf(json);
        Log.v("myApp","resultsdata" + fulldata);

        newsList = new ArrayList<String>();
        newsList2 = new ArrayList<String>();
        newsList3 = new ArrayList<String>();
        imageList = new ArrayList<String>();


        JSONObject obj = new JSONObject(json);    
        JSONObject objData = obj.getJSONObject("data");
        JSONArray jArray = objData.getJSONArray("results");


        if(jArray.length() < 1) loadLastResults();



    } catch (ClientProtocolException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }   


}


public void loadLastResults(){

    resultsFeedRequest = "website/" + chosenLeagueId + "/results?month=04&team_id=" + ChosenTeamId + "&limit=31&timestamp=" + unixTimeStamp;
    resultsFeedURL = "https://www.website.com" + resultsFeedRequest;    

     String myhash = buildHmacSignature(apiKey, resultsFeedURL);

    Date anotherCurDate = new Date();  
    SimpleDateFormat formatter = new SimpleDateFormat("MM");  
    String CurMonth = formatter.format(anotherCurDate);  

    int Int = Integer.parseInt(CurMonth);

    int MonthInt = Int -1;


    CurMonth = (String) (String.valueOf(MonthInt));



    if (CurMonth.equals("1")){

        lastMonth = "12";

    }    
     else {
        if(CurMonth.length() < 2){
            lastMonth = "0" + CurMonth;
        } else {
            lastMonth = CurMonth;
        }
    }

    Log.v("lc","month= " + CurMonth);
    Log.v("lc","LastMonth= " + lastMonth);


        HttpClient client = new DefaultHttpClient();
        HttpPost post = new HttpPost(resultsFeedURL);

        List<NameValuePair> pairs = new ArrayList<NameValuePair>();
        pairs.add(new BasicNameValuePair("requestToken", myhash));
        pairs.add(new BasicNameValuePair("apiUser", apiUser));

        try {
            post.setEntity (new UrlEncodedFormEntity(pairs));
            HttpResponse response = client.execute(post);
            BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent(), "UTF-8"));
            String json = reader.readLine();
            fulldata = String.valueOf(json);
            Log.v("myApp","resultsdata" + fulldata);

            newsList = new ArrayList<String>();
            newsList2 = new ArrayList<String>();
            newsList3 = new ArrayList<String>();
            imageList = new ArrayList<String>();


            JSONObject obj = new JSONObject(json);    
            JSONObject objData = obj.getJSONObject("data");
            JSONArray jArray = objData.getJSONArray("results");


               for(int t = 0; t < 1; t++){

                   resultsDict = jArray.getJSONObject(t);
                  HomeTeam = resultsDict.getString("hometeam");
                  AwayTeam = resultsDict.getString("awayteam");
                  HomeScore = resultsDict.getString("homescore");
                  AwayScore = resultsDict.getString("awayscore");
                  Attendance = resultsDict.getString("attendance");
                  Division = resultsDict.getString("division");

                  Log.v("lc","hometeam" + HomeTeam);
                  Log.v("lc","awayteam" + AwayTeam);


               }


        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


    }   


public class PostTask extends AsyncTask<Void, String, Boolean> {

    @Override
    protected Boolean doInBackground(Void... params) {
        boolean result = false;
        loadNewsFeed();
        loadResultsFeed();
        loadLastResults();
        publishProgress("progress");
        return result;
    }

    protected void onProgressUpdate(String... progress) {
        StringBuilder str = new StringBuilder();
            for (int i = 1; i < progress.length; i++) {
                str.append(progress[i] + " ");
            }
    }

}

public void FillData(){ 


     if (ChosenMethod.equals("Team")) {


         resultsView = LayoutInflater.from(getBaseContext()).inflate(R.layout.resultscell,
                 null);

       TextView homeTeam = (TextView) resultsView.findViewById(R.id.HomeTeam);
       homeTeam.setText(HomeTeam);

       TextView awayTeam = (TextView) resultsView.findViewById(R.id.AwayTeam);
       awayTeam.setText(AwayTeam);

       TextView homeScore = (TextView) resultsView.findViewById(R.id.HomeScore);
       homeScore.setText(HomeScore);

       TextView awayScore = (TextView) resultsView.findViewById(R.id.AwayScore);
       awayScore.setText(AwayScore);

       TextView attendance = (TextView) resultsView.findViewById(R.id.Attendence);
       attendance.setText("Att:" + Attendance);

       TextView division = (TextView) resultsView.findViewById(R.id.Division);
       division.setText(Division);

        arrayAdapter = new ArrayAdapter<String>(this, R.layout.single_item, newsList);

         String[] mStrings = (String[]) imageList.toArray(new String[imageList.size()]);
         String[] news = (String[]) newsList3.toArray(new String[newsList3.size()]);

         arrayAdapter3 = new LazyAdapter(this, mStrings, news);


            ListView list = getListView();
               list.setTextFilterEnabled(true);

               LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE );
                View header = inflater.inflate( R.layout.homeheader, list, false);
                View header2 = inflater.inflate( R.layout.homeheader2, list, false);
                View header3 = inflater.inflate( R.layout.homeheader3, list, false);


        //setListAdapter (arrayAdapter);


            adapter = new MergeAdapter();
            adapter.addView(header);
            adapter.addAdapter(arrayAdapter);
            adapter.addView(header2);
            adapter.addView(resultsView);
            adapter.addView(header3);
            adapter.addAdapter(arrayAdapter3);
            setListAdapter(adapter);



     } else {

         arrayAdapter = new ArrayAdapter<String>(this, R.layout.single_item, newsList);
            arrayAdapter2 = new ArrayAdapter<String>(this, R.layout.single_item, newsList2);
            //arrayAdapter3 = new ArrayAdapter(this, R.layout.complex_item, newsList3);

             String[] mStrings = (String[]) imageList.toArray(new String[imageList.size()]);
             String[] news = (String[]) newsList3.toArray(new String[newsList3.size()]);


             arrayAdapter3 = new LazyAdapter(this, mStrings, news);


                ListView list = getListView();
                   list.setTextFilterEnabled(true);

                   LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE );
                    View header3 = inflater.inflate( R.layout.homeheader3, list, false);


            //setListAdapter (arrayAdapter);


                adapter = new MergeAdapter();
                adapter.addView(header3);
                adapter.addAdapter(arrayAdapter3);
                setListAdapter(adapter);
         } 
}

Answer 1

盲目假设......！（没有StackTrace报告）

在onPostExecute()中实施AsyncTask并在其中添加FillData()方法..当您的doInBackground()完成控制后，onPostExecute()会自动进入..然后填写你的UI部分..

Answer 2

在FillData()

中调用onPostExecute Method of AsyncTask方法

应该是::

public class PostTask extends AsyncTask<Void, String, Boolean> {

    @Override
    protected Boolean doInBackground(Void... params) {
        boolean result = false;
        loadNewsFeed();
        loadResultsFeed();
        loadLastResults();
        publishProgress("progress");
        return result;
    }


    protected void onProgressUpdate(String... progress) {
        StringBuilder str = new StringBuilder();
            for (int i = 1; i < progress.length; i++) {
                str.append(progress[i] + " ");
            }
    }

        @Override
    protected void onPostExecute(Boolean result) {
        super.onPostExecute(result);

         fillData();
    }
}

Answer 3

您应该使用AsyncTask的其他方法来更新UI。

protected void onPostExecute(Long result) {
    showDialog("Downloaded " + result + " bytes");
}

Answer 4

在asynctask中添加方法，即

public void onPostExecute(Void result){}

在其中解除对话并致电您的fillData()

Answer 5

您可以使用ProgressDialog，直到服务器的完整数据到达您的结尾并填写数据......

请阅读this。

如果有任何问题，请告诉我。

谢谢，

HAPS。

AsyncTask检测是否完成

5 个答案: