Android 数组列表如何使用

Question

所以我有一个标记列表，我需要弄清楚如何处理它们。我已经搜索了几个小时，但没有明确说明如何使用这些信息或如何从列表中获取信息。请解释或分解我的代码并告诉我它到底是如何工作的。这样我就可以在 map 上设置标记。

这就是我将标记添加到列表中的方法。现在，在 onPostExecute 上，我需要将它们显示在我的 map 上。但我不确定如何获得它们。我从服务器发送到我的应用程序的大约有 50 个标记。

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);

编辑:源代码

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 错误:

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

Answer 1

此代码将遍历整个列表。

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

编辑:这是来自开发人员网站的一些代码。这是如何向 map 添加标记的示例。

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

您已经在 doInBackground 方法中执行此操作。那么到底是什么问题呢？

编辑 2:尝试使用此代码代替您的代码，看看它是否有效。

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;
         }
      }