JSON数据片段上的ListView

Question

我正在尝试从一个片段中的JSON数据创建一个ListView，但是要使其正确显示却遇到了种种麻烦：

领域

public class Endpoints {

//constants for field references
public static final String PUBLICURL = "publicURL";
public static final String REGION = "region";
public static final String TYPE = "type";
public static final String NAME = "name";

//fields
String publicURL;
String region;
String type;
String name;


//getters and setters
public String getPublicURL() {
    return publicURL;
}

public String getRegion() {
    return region;
}

public String getType() {
    return type;
}

public String getName() {
    return name;
}

public void setPublicURL(String publicURL) {
    this.publicURL = publicURL;
}

public void setRegion(String region) {
    this.region = region;
}

public void setType(String type) {
    this.type = type;
}

public void setName(String name) {
    this.name = name;
}

解析器

public class EndpointsParser {
public static List<Endpoints> parseFeed(String content) {

    try {
        JSONArray ar = new JSONArray(content);
        List<Endpoints> endpointsList = new ArrayList<>();

        for (int i = 0; i < ar.length(); i++) {

            JSONObject obj = ar.getJSONObject(i);
            Endpoints endpoint = new Endpoints();

            endpoint.setName(obj.getString("name"));
            endpoint.setType(obj.getString("type"));
            endpoint.setRegion(obj.getString("region"));
            endpoint.setPublicURL(obj.getString("publicURL"));

            endpointsList.add(endpoint);
        }

        return endpointsList;
    } catch (JSONException e) {
        e.printStackTrace();
        return null;
    }

}

适配器

public class EndpointsAdapter extends ArrayAdapter<Endpoints> {

private Context context;
private List<Endpoints> endpointsList;

public EndpointsAdapter(Context context, int resource, List<Endpoints> objects){
    super(context, resource, objects);
    this.context = context;
    this.endpointsList = objects;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {

    LayoutInflater inflater =
            (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
    View view = inflater.inflate(R.layout.endpoint_list, parent, false);

    return view;
}

片段OnCreateView

    @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    String endpoints = "{\"access\": {\"token\": {\"issued_at\": \"2014-11-07T01:32:21.151767\", \"expires\": \"2014-11-07T02:32:21Z\", \"id\": \"1a7bdd8ce9604dd199c86f905092c59e\", \"tenant\": {\"description\": \"Admin\", \"enabled\": true, \"id\": ...]}}}";
    View rootView = inflater.inflate(R.layout.fragment_overview, container, false);
    TextView textView = (TextView) rootView.findViewById(R.id.overviewTV);
    ListView listView = (ListView) rootView.findViewById(R.id.overviewLV);
    //For display testing 
    //textView.setText(endpoints);
    List<Endpoints> endpointsList;
    endpointsList = EndpointsParser.parseFeed(endpoints);
    EndpointsAdapter adapter = new EndpointsAdapter(getActivity(), R.layout.endpoint_list, endpointsList);
    listView.setAdapter(adapter);
    return rootView;
}

我无法使其正常工作，并且从Exception尚不清楚错误来自哪里：

11-07 04:48:54.751    2627-2627/com.stackerz.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.stackerz.app, PID: 2627
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.stackerz.app/com.stackerz.app.Stackerz}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
            at android.widget.ListView.setAdapter(ListView.java:480)
            at android.app.ListFragment.setListAdapter(ListFragment.java:240)
            at android.app.ListFragment.ensureList(ListFragment.java:424)
            at android.app.ListFragment.onViewCreated(ListFragment.java:203)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:904)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
            at android.app.BackStackRecord.run(BackStackRecord.java:684)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
            at android.app.Activity.performStart(Activity.java:5240)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2157)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            at android.app.ActivityThread.access$800(ActivityThread.java:135)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

您需要在适配器中@Override getCount()方法。

@Override
public int getCount() {
    return endpointsList.size();
}