Question

我有一个简单的程序，可以从Google Images API获取JSON数据。它将该JSON中的所有URL存储在ArrayList中。我创建了一个AsyncTask来处理这个问题。当我运行该程序时，我收到以下错误：

java.lang.RuntimeException: An error occured while executing doInBackground()
            at android.os.AsyncTask$3.done(AsyncTask.java:299)
            at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
            at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
            at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
            at java.util.concurrent.FutureTask.run(FutureTask.java:137)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
            at java.lang.Thread.run(Thread.java:856)
     Caused by: java.lang.NullPointerException
            at com.example.bab.googleimagesapi.MainActivity$myTask.doInBackground(MainActivity.java:84)
            at com.example.bab.googleimagesapi.MainActivity$myTask.doInBackground(MainActivity.java:58)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
            at java.util.concurrent.FutureTask.run(FutureTask.java:137)
            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
            at java.lang.Thread.run(Thread.java:856)

它表示第58和84行有一个NullPointerException。这是我的Asynctask的代码，我已经注释了第58和84行，所以你可以找到它们。

    private class myTask extends AsyncTask<Void, Void, ArrayList<String> > {  **//LINE 58**

        @Override
        protected ArrayList<String> doInBackground(Void... params) {
            String imageUrl = "x";
            String query = editText.getText().toString();            //get users search query
            query = query.replaceAll(" ", "%20");
            try {
                URL url = new URL("https://ajax.googleapis.com/ajax/services/search/imagesv=1.0&q=" + query + "&userip=INSERT-USER-IP");
                URLConnection connection = url.openConnection();
                connection.addRequestProperty("referer", "www.github.com");
                String line;
                StringBuilder builder = new StringBuilder();

                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                while ((line = reader.readLine()) != null) {
                    builder.append(line);
                }

                try {
                    JSONObject jsonObject = new JSONObject(builder.toString());
                    JSONObject sub = jsonObject.getJSONObject("responseData");
                    JSONArray results = sub.getJSONArray("results");
                    for(int x = 0; x < results.length(); x++) {
                        JSONObject jsonImage = results.getJSONObject(x);
                        imageUrl = jsonImage.getString("url");
                        urlList.add(imageUrl);        **//LINE 84**
                    }
                    return urlList;
                } catch (JSONException e) {
                    e.printStackTrace();
                }

            } catch (MalformedURLException e) {
                e.printStackTrace();
                // textResult = e.toString();
            } catch (IOException e) {
                e.printStackTrace();
                //textResult = e.toString();
            }
            return null;
        }


        protected void onPostExecute(ArrayList<String> list) {

            for(int x = 0; x < list.size(); x++){
                textView.append(list.get(x));
            }
        }
    }

我是初次使用AsyncTask和Android的新手，所以我感谢任何帮助！

Answer 1

您需要在使用之前初始化urlList：

urlList = new ArrayList<>();

Answer 2

您需要在urlList

中初始化myTask

urlList = new ArrayList<>();

或宣布为最终版。

另外，我不建议您在Android上使用AsyncTask。在这里阅读更多相关信息： http://simonvt.net/2014/04/17/asynctask-is-bad-and-you-should-feel-bad/

Asynctask并将一个arraylist传递给它给我错误

2 个答案: