Android arraylist how to use

Question

So I have a list of markers that I need to figure out what to do with. I have searched for a few hours now, but nothing clearly states how to use the information or how to get the information from the list. Please explain or break down my code and inform me on how it exactly works. So I can set my markers on my map.

This is how I add my markers to my list. Now on onPostExecute I need to display them on my map. But I am unsure how to get them. There is about 50 markers that I send to my app from my server.

List<Marker> markers = new ArrayList<Marker>();
Marker marker = map.addMarker(new MarkerOptions()
            .position(location)
            .title(getName)
            .snippet(getDesc)
            .icon(BitmapDescriptorFactory
                      .fromResource(R.drawable.icon)));

            markers.add(marker);

EDIT: SOURCE CODE

private class PrefetchData extends AsyncTask<String, Void, String> 
   {

        @Override
        protected void onPreExecute() 
        {
            super.onPreExecute();    
        }

        protected void onPostExecute(Void result) 
        {
            for (int i = 0; i < markers.size(); i++) 
            {
                Marker currentMarker = markers.get(i);
                // do what you want with the current marker
            }
        }

        protected String doInBackground(String... params) 
        {
            JsonParser jsonParser = new JsonParser();
            String json = jsonParser.getJSONFromUrl("http://www.mywebsite.com/test.json");

            if (json != null) 
            {
                try 
                {
                    JSONObject parent = new JSONObject(json);
                    JSONArray eventDetails = parent.getJSONArray("maps");

                    for(int i=0; i < eventDetails.length(); i++)
                    {
                        object = eventDetails.getJSONObject(i);

                        String getName = object.getString("name");
                        String getAddy =object.getString("addy");
                        String getHours = object.getString("hours");
                        String getDesc = object.getString("desc");
                        String getLat = object.getString("lat");
                        String getLong = object.getString("long");

                        Log.e("JSON", "> " + getName + getAddy + getHours + getDesc + getLat + getLong );

                        double lat_ = Double.valueOf(getLat);
                        double lng_ = Double.valueOf(getLong);              

                        LatLng location = new LatLng(lat_, lng_);

                        Marker marker = map.addMarker(new MarkerOptions()
                                .position(location)
                                .title(getName)
                                .snippet(getDesc)
                                .icon(BitmapDescriptorFactory
                                       .fromResource(R.drawable.icon)));

                        markers.add(marker);

                        // creating connection detector class instance
                        cd = new Connection(getApplicationContext());
                    }
                }
                catch (JSONException e) 
                {
                    // TODO Auto-generated catch block
                    Log.e("Json Error", "Error: " + e.toString());
                        e.printStackTrace();
                }
             }

            return null;
         }
      }

LOGCAT ERRORS:

01-26 01:27:43.082: E/AndroidRuntime(8209): FATAL EXCEPTION: main
01-26 01:27:43.082: E/AndroidRuntime(8209): Process: com.databasedemo, PID: 8209
01-26 01:27:43.082: E/AndroidRuntime(8209): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.databasedemo/com.databasedemo.Map}: java.lang.NullPointerException
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.os.Looper.loop(Looper.java:136)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.ActivityThread.main(ActivityThread.java:5017)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at java.lang.reflect.Method.invokeNative(Native Method)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at java.lang.reflect.Method.invoke(Method.java:515)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at dalvik.system.NativeStart.main(Native Method)
01-26 01:27:43.082: E/AndroidRuntime(8209): Caused by: java.lang.NullPointerException
01-26 01:27:43.082: E/AndroidRuntime(8209):     at com.databasedemo.Map.onCreate(Map.java:121)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.Activity.performCreate(Activity.java:5231)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-26 01:27:43.082: E/AndroidRuntime(8209):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
01-26 01:27:43.082: E/AndroidRuntime(8209):     ... 11 more

You are getting a NullPointerException at com.databasedemo.Map.onCreate(Map.java:121). So check there. — Luis
– Luis, Commented Jan 26, 2014 at 6:39

Ogen · Accepted Answer · 2014-01-26 08:04:55Z

3

This code will iterate through the whole list.

for (int i = 0; i < markers.size(); i++) {
    Marker currentMarker = markers.get(i);
    // do what you want with the current marker
}

EDIT: This is some code from the developers website. It's an example of how to add a marker to a map.

Marker marker = map.addMarker(new MarkerOptions()
     .position(new LatLng(37.7750, 122.4183))
     .title("San Francisco")
     .snippet("Population: 776733"));

You are already doing this in your doInBackground method. So what is the problem exactly?

EDIT 2: Try using this code in place of yours, and see if it works.

private class PrefetchData extends AsyncTask<String, Void, String>  {

        private LatLng location;
        private String getName;
        private String getDesc;
        private List<Object[]> markerOptions;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();    
        }

        protected void onPostExecute(Void result) {
            for (int i = 0; i < markerOptions.size; i++) {
                Marker marker = map.addMarker(new MarkerOptions()
                                .position(markerOptions.get(i)[0])
                                .title(markerOptions.get(i)[1])
                                .snippet(markerOptions.get(i)[2])
                                .icon(BitmapDescriptorFactory
                                       .fromResource(R.drawable.icon)));

                        markers.add(marker);
            }
        }

        protected String doInBackground(String... params) {
        markerOptions = new ArrayList<Object[]>();
            JsonParser jsonParser = new JsonParser();
            String json = jsonParser.getJSONFromUrl("http://www.mywebsite.com/test.json");

            if (json != null) {
                try {
                    JSONObject parent = new JSONObject(json);
                    JSONArray eventDetails = parent.getJSONArray("maps");

                    for(int i=0; i < eventDetails.length(); i++) {
                        object = eventDetails.getJSONObject(i);

                        getName = object.getString("name");
                        String getAddy =object.getString("addy");
                        String getHours = object.getString("hours");
                        getDesc = object.getString("desc");
                        String getLat = object.getString("lat");
                        String getLong = object.getString("long");

                        Log.e("JSON", "> " + getName + getAddy + getHours + getDesc + getLat + getLong );

                        double lat_ = Double.valueOf(getLat);
                        double lng_ = Double.valueOf(getLong);              

                        location = new LatLng(lat_, lng_);

                        markerOptions.add(new Object[]{location, getName, getDesc});

                        // creating connection detector class instance
                        cd = new Connection(getApplicationContext());
                    }
                }
                catch (JSONException e) {
                    // TODO Auto-generated catch block
                    Log.e("Json Error", "Error: " + e.toString());
                        e.printStackTrace();
                }
             }

            return null;
         }
      }

edited Jan 26, 2014 at 8:04

answered Jan 26, 2014 at 6:11

Ogen

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14 Comments

Jayce Over a year ago

Okay still doesn't make since to me, please see my edit for updated code. Basically my doinbackground gets the locations and info from my website and i need to display the markers on the google map.

Ogen Over a year ago

Please see my edit, as far as I know, you are already displaying the markers on the google map in your doinbackground

Jayce Over a year ago

You can't add markers to the google map from the doinbackground cause it's on the UI, so you have to do it on the postexecute. I am trying to add the information for my markers to a list, then get them on postexecute and then display them on the map.

Ogen Over a year ago

@user3186578 So what you're trying to do is create the marker without adding it to the map. You want to create it in your doInBackground first, and THEN add it the map. In that case, please take a look at this question - it is relevant: stackoverflow.com/questions/16481359/…

Inzimam Tariq IT Over a year ago

I have no "ask question" privilege so I can't ask question. Anyway thanks for your response My problem has solved

|

Matt Clark · Accepted Answer · 2014-01-26 06:07:00Z

0

Simply call .get(index).

To get the count, use .size()

Marker marker = markers.get(index);

answered Jan 26, 2014 at 6:07

Matt Clark

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Comments

java seeker · Accepted Answer · 2014-01-26 06:14:21Z

0

int size=markers.size();

for(int m=0 ; m < size; ++m)
 Marker obj= markers.get(index);

or you can use iterator

Iterator<Marker> iterator = markers.iterator();
        while (iterator.hasNext()) {
            Marker m=iterator.next();
        }

answered Jan 26, 2014 at 6:14

java seeker

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Comments

Luis · Accepted Answer · 2014-01-26 06:30:42Z

0

for (Marker marker : markers){
     LatLng latlng = marker.getPostion();
     String snippet = marker.getSnippet();
     String title = marker.getTitle()
}

answered Jan 26, 2014 at 6:30

Luis

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Comments

benka · Accepted Answer · 2014-10-28 10:07:00Z

Display showInfoWindow without clicking on marker android google map api v2

Declare markersList in outside of the class

List<Marker> markersList= new ArrayList<Marker>();

Adding marker to markersList

Marker marker=map.addMarker(new MarkerOptions().position(ll)
        .title(description).snippet("Jersey No :"+deviceID.split("-")[2])
        .icon(bitmapMarker));
markersList.add(marker);  // markersList --ArrayList declared outside class

Without selecting marker to showing marker infowindow
Here I used spinner to select the position

@Override
public boolean onNavigationItemSelected(int itemPosition, long itemId) {

    Marker currentMarker = markersList.get(itemPosition);
    LatLng latlng = currentMarker.getPosition();
    CameraUpdate update = CameraUpdateFactory.newLatLngZoom(latlng, 19F); 
    map.animateCamera(update);
    currentMarker.showInfoWindow();

}

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