java - 空对象引用上的java.lang.String com.parse.ParseFile.getUrl()'

我在Logcat中收到此运行时错误：

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.parse.ParseFile.getUrl()' on a null object reference
    at com.google.geoplace.MainActivity$RemoteDataTask.doInBackground(MainActivity.java:68)
    at com.google.geoplace.MainActivity$RemoteDataTask.doInBackground(MainActivity.java:36)
    at android.os.AsyncTask$2.call(AsyncTask.java:288)
    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
    at java.lang.Thread.run(Thread.java:818) 

这是MainActivity类

public class MainActivity extends Activity {
    // Declare Variables
    ListView listview;
    List<ParseObject> ob;
    ProgressDialog mProgressDialog;
    ListViewAdapter adapter;
    private List<PlaceFilter> worldpopulationlist = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Get the view from listview_main.xml
        setContentView(R.layout.activity_main);
        // Execute RemoteDataTask AsyncTask
        new RemoteDataTask().execute();
    }

    // RemoteDataTask AsyncTask
    private class RemoteDataTask extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Create a progressdialog
            mProgressDialog = new ProgressDialog(MainActivity.this);
            // Set progressdialog title
            mProgressDialog.setTitle("Parse.com Custom ListView Tutorial");
            // Set progressdialog message
            mProgressDialog.setMessage("Loading...");
            mProgressDialog.setIndeterminate(false);
            // Show progressdialog
            mProgressDialog.show();
        }

        @Override
        protected Void doInBackground(Void... params) {
            // Create the array
            worldpopulationlist = new ArrayList<PlaceFilter>();
            try {
                // Locate the class table named "Country" in Parse.com
                ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                        "geo_filters");
                // Locate the column named "ranknum" in Parse.com and order list
                // by ascending
                ob = query.find();
                for (ParseObject geo_filters : ob) {
                    // Locate images in flag column
                    ParseFile image = (ParseFile) geo_filters.get("FilterFile");

                    PlaceFilter map = new PlaceFilter();
                    map.setPlaceName((String) geo_filters.get("PlaceName"));
                    map.setFilterFile(image.getUrl());
                    worldpopulationlist.add(map);
                }
            } catch (ParseException e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            // Locate the listview in listview_main.xml
            listview = (ListView) findViewById(R.id.listView);
            // Pass the results into ListViewAdapter.java
            adapter = new ListViewAdapter(MainActivity.this,
                    worldpopulationlist);
            // Binds the Adapter to the ListView
            listview.setAdapter(adapter);
            // Close the progressdialog
            mProgressDialog.dismiss();
        }
    }
}

这是PlaceFilter类：

public class PlaceFilter {
    private String PlaceName;
    private String FilterFile;

    public String getPlaceName() {
        return PlaceName;
    }

    public void setPlaceName(String PlaceName) {
        this.PlaceName = PlaceName;
    }

    public String getFilterFile() {
        return FilterFile;
    }

    public void setFilterFile(String FilterFile) {
        this.FilterFile = FilterFile;
    }
}

它从解析后端返回PlaceName，而没有图像，PlaceFilter.java中存在一些语法错误。纠正错误后，我得到运行时错误。

最佳答案

直接原因是geo_filters.get("FilterFile")返回null。
下一步，您必须检查从“ geo_filters”中检索到的ParseObject，以及为什么其中某些没有“ FilterFile”值。