st_dec st_dec - 4 months ago 31
Android Question

How to use ProgressDialog to show JSON parsing progress?

I want to show progress of some JSON parsing using with progress bar. I've never used it and found some examples in the Internet. So, I try to realize it but application crashes when parsing starts. Here is code:

public class Parser extends Activity {

public static String w_type1 = "news";
public static String w_type2 = "events_put";
public ListView lv;
ArrayList<Widget> data = new ArrayList<Widget>();
WidgetAdapter wid_adptr = new WidgetAdapter(this, data);

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_parser);


lv = (ListView) this.findViewById(R.id.list);
lv.setAdapter(wid_adptr);
new ParseTask().execute();

}

private class ParseTask extends AsyncTask<Void, Void, String> {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String resultJson = "";

public ProgressDialog dialog;
Context ctx;

protected void onPreExecute() {
dialog = new ProgressDialog(ctx);
dialog.setMessage("Pasring...");
dialog.setIndeterminate(true);
dialog.setCancelable(true);
dialog.show();
}

@Override
protected String doInBackground(Void... params) {
try {
URL url = new URL("http://api.pandem.pro/healthcheck/w/");

urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();

InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();

reader = new BufferedReader(new InputStreamReader(inputStream));

String line;
while ((line = reader.readLine()) != null) {
buffer.append(line);
}

resultJson = buffer.toString();

} catch (Exception e) {
e.printStackTrace();
}
return resultJson;
}

@Override
protected void onPostExecute(String strJson) {
super.onPostExecute(strJson);


JSONObject dataJsonObj = null;

try {
dataJsonObj = new JSONObject(strJson);
JSONArray widgets = dataJsonObj.getJSONArray("widgets");

for (int i = 0; i < widgets.length(); i++) {
JSONObject widget = widgets.getJSONObject(i);

String wType = widget.getString("type");

if (wType.equals(w_type1) || wType.equals(w_type2)) {

String title = widget.getString("title");
String desc = widget.getString("desc");
String img_url = "";
if (widget.has("img")) {
JSONObject img = widget.getJSONObject("img");
img_url = img.getString("url");
}
data.add(new Widget(wType, title, desc, img_url));
//wid_adptr.notifyDataSetChanged();
}
}

} catch (JSONException e) {
e.printStackTrace();
}

dialog.dismiss();
}
}
}


If i don't use ProgressDialog (just comment or delete dialog code) application works correctly. How can I fix it?

Answer

Without any logcat it's difficult to help, but it seems that your ctx is null so

dialog = new ProgressDialog(ctx);

the dialog can't be created.

Try to add constructor to the AsyncTask and pass the context here, something like:

private class ParseTask extends AsyncTask<Void, Void, String> {
...
    public ParseTask(Context ctx) {
        this.ctx = ctx;
    }
...
}

To start the task:

new ParseTask(this).execute();
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