Question

我有一个问题，我的progressdialog，我的应用程序从json搜索数据，然后对话框来了，但我在收集数据的时候想要它。我的错在哪里？

有编辑的代码 logcat（致命的例外：主要显示java.lang.NullPointerException） JSON（[{“name”：“Test”}]）编辑：

public class MainActivity extends ListActivity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    new TheTask().execute();
}
class TheTask extends AsyncTask<Void, Void, JSONObject> {
    InputStream is = null;
    String result = "";
    JSONObject jArray = null;

    ProgressDialog pd;

    @Override
    protected void onPostExecute(JSONObject result) {
        super.onPostExecute(result);
        pd.dismiss();
        JSONObject jObject = result;
        try {
            String aJsonString = jObject.getString("name");
        } catch (JSONException e) {
            e.printStackTrace();
        }
        setListAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, (List<String>) result));
        // parse and set List adapter here
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pd = ProgressDialog.show(MainActivity.this, "dialog title",
                "dialog message", true);
    }

    @Override
    protected JSONObject doInBackground(Void... arg0) {
        try {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost("***");
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();

        } catch (Exception e) {
            Log.e("log_tag", "Error in http connection " + e.toString());
        }

        // Convert response to string
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            result = sb.toString();
        } catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
        }

        try {

            jArray = new JSONObject(result);
        } catch (JSONException e) {
            Log.e("log_tag", "Error parsing data " + e.toString());
        }

        return jArray;
    }
}

Answer 1

Thread.sleep(50);

你正在阻止它的ui线程上调用sleep。删除它。

使用AsyncTask代替Thread。

http://developer.android.com/reference/android/os/AsyncTask.html

在onPreExecute中显示进度对话框。在doInbackground中处理您的http请求。在onPostExecute中关闭对话框并相应地更新ui。

调用

 new TheTask().execute();

然后

 class TheTask extends AsyncTask<Void, Void, Void>    {

        ProgressDialog pd;

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            progress.dismiss();

        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
             progress = ProgressDialog.show(MainActivity.this, "dialog title",
                            "dialog message", true);
        }

        @Override
        protected Void doInBackground(Void... arg0) {
            // http request
            return null;
        }   
    }

编辑：

public class MainActivity extends ListActivity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    new TheTask().execute();
    }
class TheTask extends AsyncTask<Void, Void, JSONObject> {
    InputStream is = null;
    String result = "";
    JSONObject jArray = null;

    ProgressDialog pd;

    @Override
    protected void onPostExecute(JSONObject result) {
        super.onPostExecute(result);
        pd.dismiss();
        // parse and set List adapter here
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pd = ProgressDialog.show(MainActivity.this, "dialog title",
                "dialog message", true);
    }

    @Override
    protected JSONObject doInBackground(Void... arg0) {
        try {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost("******");
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();

        } catch (Exception e) {
            Log.e("log_tag", "Error in http connection " + e.toString());
        }

        // Convert response to string
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            result = sb.toString();
        } catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
        }

        try {

            jArray = new JSONObject(result);
        } catch (JSONException e) {
            Log.e("log_tag", "Error parsing data " + e.toString());
        }

        return jArray;
    }
}
}

EDIT2：

   class TheTask extends AsyncTask<Void, Void, JSONArray> {
    InputStream is = null;
    String result = "";
    JSONArray jArray = null;

    ProgressDialog pd;

    @Override
    protected void onPostExecute(JSONArray result) {
        super.onPostExecute(result);
        pd.dismiss();
        ArrayList<String> list= new ArrayList<String>();
        try
        {
        for(int i=0;i<result.length();i++)
        {

            JSONObject jb = result.getJSONObject(i) ;
            String name = jb.getString("name");
            list.add(name);
        }
        }catch(Exception e)
        {
            e.printStackTrace();
        }
        setListAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, list));
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pd = ProgressDialog.show(MainActivity.this, "dialog title",
                "dialog message", true);
    }

    @Override
    protected JSONArray doInBackground(Void... arg0) {
        try {
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost("******");
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();

        } catch (Exception e) {
            Log.e("log_tag", "Error in http connection " + e.toString());
        }

        // Convert response to string
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            result = sb.toString();
        } catch (Exception e) {
            Log.e("log_tag", "Error converting result " + e.toString());
        }

        try {

            jArray = new JSONArray(result);
        } catch (JSONException e) {
            Log.e("log_tag", "Error parsing data " + e.toString());
        }

        return jArray;
    }
}
}

Answer 2

您在Thread.sleep(50)上致电UI Thread，以便UI冻结，直至完成。将您的操作移至AsyncTask中的sleep()和doInBackground()。将所有网络代码也放在doInBackground()中。

您可以使用AsyncTasks其他方法更新UI。

See this answer for an example of AsyncTask如果您不熟悉

AsyncTask Docs

进度对话框android json

2 个答案: