Question

我试图将我在异步任务类中获得的字符串传递回我的主要活动，但是当我传递字符串结果时（我知道它不是null，因为在将字符串传递给接口之前将其记录下来）输出它应该的东西），我得到一个nullPointerException，它说我不能将null对象传递给接口方法。

这是AsyncTask类，

public class APICalls extends AsyncTask<String,Void, String> {
    public AsyncResponse delegate;

    protected String doInBackground(String... zipcodes){
        String zipcode = zipcodes[0];
        String apikey = "6562c36e87ba41f6bc887104d1e82eb8";
        String baseURL = "https://congress.api.sunlightfoundation.com";
        String zipCodeAddition = "/legislators/locate?apikey="+apikey + "&zip=" + zipcode;
        String url = baseURL + zipCodeAddition;
        String results = "";
        URL apiurl = null;
        try {
            apiurl = new URL(url);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }
        HttpsURLConnection urlConnection = null;
        try {
            urlConnection = (HttpsURLConnection) apiurl.openConnection();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            InputStream in = new BufferedInputStream(urlConnection.getInputStream());
            int data = in.read();
            while(data != -1){
                results += String.valueOf((char) data);
                data = in.read();
            }
            in.close();

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            urlConnection.disconnect();
        }
        return results;
    }
protected void onPostExecute(String result){
        String results = result;
        try {
            delegate.processFinish(results);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

行delegate.processFinish（results）;中发生错误。当我记录结果字符串时，它不是null。界面是：

public interface AsyncResponse {
    void processFinish(String output) throws IOException;
}

然后在主要活动中我实现了接口并使用方法：

public void processFinish(String output) throws IOException {
    Log.v("++++++++", output);
}

Answer 1

您获得NPE不是因为output是null，而是因为delegate。你永远不会初始化它。

获取：“java.lang.NullPointerException”但我知道对象是在AsyncTask中实例化的

1 个答案: