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我正在调用从数据库中获取数据并输出以下 JSON 的 Web 服务：

{"eventId":"1","eventTitle":"opening ceremony","eventCategory":"store","eventSubCategory":"clothing","eventDescription":"This is an event description of some kid for the first event","eventDate":"13/05/2012","eventTime":"14:52","eventAddress":"49 somerset road","eventCity":"southsea","eventCountry":"UK","eventWebsite":"www.nxtldn.com","eventEmail":"lg@nxtldn.com","eventPhone":"07757491567","eventKeywords":"clothes, street, wear, heart, love"},{"eventId":"2","eventTitle":"cupcakes","eventCategory":"Store","eventSubCategory":"food","eventDescription":"This is an event description of some kid for the second event","eventDate":"17/05/2012","eventTime":"11:22","eventAddress":"12 cleveleys road","eventCity":"london","eventCountry":"UK","eventWebsite":"www.ashshort.com","eventEmail":"ashshort@short.com","eventPhone":"0778514562","eventKeywords":"cupcakes, store, london, hipster"}]

我附加的（我已经使用http://jsonlint.com/测试了 JSON 是否有效）：

{"Events":[{"eventId":"1","eventTitle":"opening ceremony","eventCategory":"store","eventSubCategory":"clothing","eventDescription":"This is an event description of some kid for the first event","eventDate":"13/05/2012","eventTime":"14:52","eventAddress":"49 somerset road","eventCity":"southsea","eventCountry":"UK","eventWebsite":"www.nxtldn.com","eventEmail":"lg@nxtldn.com","eventPhone":"07757491567","eventKeywords":"clothes, street, wear, heart, love"},{"eventId":"2","eventTitle":"cupcakes","eventCategory":"Store","eventSubCategory":"food","eventDescription":"This is an event description of some kid for the second event","eventDate":"17/05/2012","eventTime":"11:22","eventAddress":"12 cleveleys road","eventCity":"london","eventCountry":"UK","eventWebsite":"www.ashshort.com","eventEmail":"ashshort@short.com","eventPhone":"0778514562","eventKeywords":"cupcakes, store, london, hipster"}]}

我使用 AsyncTask 调用它

public class EventSync extends AsyncTask<String, Integer, EventsList> {

EventsList elist1 = new EventsList();

@Override
protected EventsList doInBackground(String... urls) {
    String tempurl = urls[0];
    String output = "";
    InputStream is = null;
    StringBuilder sb = new StringBuilder();
    EventsList list = new EventsList();
    try
    {
        URL url = new URL(tempurl);
        HttpURLConnection con = (HttpURLConnection) url.openConnection();
        con.connect();
        is = con.getInputStream();

        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        String line = null;

        while((line = reader.readLine()) != null)
        {
            sb.append(line + "\n");
        }

    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
    finally
    {
        try
        {
            is.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }

    output = sb.toString();
    String json = "{\"Events\":" + output + "}";
    System.out.println(json);
    Gson gson = new Gson();
// When debugging this is the line I believe it fails on, It points to a bit of memory but the list is empty.
    EventsList jsonlist = gson.fromJson(json, EventsList.class);

    return jsonlist;
}

@Override 
protected void onPostExecute(EventsList list)
{

    System.out.println("in on post");
    for (Event event : list.getEvents())
    {
        System.out.println(event.getEventId());
    }
}}

public class EventsList {

public EventsList(){

}

private List<Event> events;

public List<Event> getEvents()
{
    return events;
}

public void setEventsList(List<Event> events)
{
    this.events = events;
}}


public class Event {

private String eventId;
private String eventTitle;
private String eventCategory;
private String eventSubCategory;
private String eventDescription;
private String eventDate;
private String eventTime;
private String eventAddress;
private String eventCity;
private String eventCountry;
private String eventWebsite;
private String eventEmail;
private String eventPhone;
private String eventKeywords;

public Event()
{

}

// ALL GETS AND SETS

目前我只是想测试它是否会在我使用自定义适配器填充列表视图之前返回。但不幸的是，我收到以下错误：

11-10 23:37:08.315: E/AndroidRuntime(5592): FATAL EXCEPTION: main
11-10 23:37:08.315: E/AndroidRuntime(5592): java.lang.NullPointerException
11-10 23:37:08.315: E/AndroidRuntime(5592):     at com.nxtldn.trill.EventSync.onPostExecute(EventSync.java:71)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at com.nxtldn.trill.EventSync.onPostExecute(EventSync.java:1)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at android.os.AsyncTask.finish(AsyncTask.java:631)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at android.os.Looper.loop(Looper.java:137)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at android.app.ActivityThread.main(ActivityThread.java:4745)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at java.lang.reflect.Method.invokeNative(Native Method)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at java.lang.reflect.Method.invoke(Method.java:511)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-10 23:37:08.315: E/AndroidRuntime(5592):     at dalvik.system.NativeStart.main(Native Method)

我是android新手，所以我不确定是否有更好的方法或者正确的方法是什么。

为什么 GSON 不接受并返回空指针是我的 JSON 结构的原因吗？

非常感谢任何可以提供帮助的人:)

4

3 回答 3

1

尝试改变

EventsList jsonlist = gson.fromJson(json, EventsList.class);

到

Event[] jsonlist = gson.fromJson(json, Event[].class);

这是假设您在 Web 服务中使用了 Event 类型的数组（如上图所示）来创建此 json。我认为当前的问题是您的 json 字符串与 EventList 类不匹配，因此返回 null。确保您的服务和 android 项目中的 Event 类匹配。

于 2012-11-20T15:38:23.693 回答
0

在 EventsList 中，您期望一个 List(Collection) 事件，但您附加的 JSON 实际上是一个对象："{\"Events\":" + output + "}"; 也许您希望它看起来像这样：

"{\"Events\":[" + output + "]}";

这会将您的单个事件放入一系列潜在事件中。您的用例令人困惑，我不确定您为什么要将单个 JSON 对象放入数组中，但也许我缺少更多细节。

于 2012-11-16T19:46:54.777 回答
0

I found it was due to me adding "/n" to my string builder, creating the new line and chopping off the final } of the json. Thanks everyone

于 2012-11-27T16:40:10.643 回答