Question

出现此错误：

 java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:200)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
at java.lang.Thread.run(Thread.java:1027)
Caused by: java.lang.NullPointerException
at com.Wahoo.BrowseListActivity$DownloadSite.doInBackground(BrowseListActivity.java:79)
at com.Wahoo.BrowseListActivity$DownloadSite.doInBackground(BrowseListActivity.java:1)
at android.os.AsyncTask$2.call(AsyncTask.java:185)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
... 4 more

这是我的AsyncTask ...它在特定时间仅针对某些用户崩溃...不确定原因。也许他们在查询中丢失了他们的互联网连接？我在这做错了什么？这是我的代码：

private class DownloadSite extends AsyncTask<String, Integer, String> {
        private HttpResponse response;
        private InputStream in;
        private Context context;
        private String html;
        private ProgressDialog progress;


        @Override
        protected String doInBackground(String... params) {

            in = null;

            String url = "aURLGOESHERE_BUTI'MCENSORING"                                 + params[0] + "";

            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet(url);
            HttpResponse response = null;

            try {
                response = client.execute(request);
            } catch (ClientProtocolException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }

            try {
                in = response.getEntity().getContent();
            } catch (IllegalStateException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (Exception e) {

                e.printStackTrace();

            }
            html = null;

            BufferedReader reader = null;
            try {
                reader = new BufferedReader(new InputStreamReader(in));
            } catch (Exception e) {

                this.publishProgress();
                this.cancel(true);

                e.printStackTrace();
            }

            StringBuilder str = new StringBuilder();
            String line = null;

            try {
                while ((line = reader.readLine()) != null) {
                    str.append(line);
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            try {
                in.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            html = params[0] + str.toString();

            return html;

        }

        @Override
        protected void onPreExecute() {

            progress = new ProgressDialog(BrowseListActivity.this);
            progress.setIndeterminate(true);
            progress.setMessage("Loading...");
            progress.setProgressStyle(ProgressDialog.STYLE_SPINNER);
            progress.show();
        }

        @Override
        protected void onProgressUpdate(Integer... progress) {

            CharSequence text = "Connection interrupted...please try again";
            int duration = Toast.LENGTH_LONG;
            Toast toast = Toast.makeText(getApplicationContext(), text,
                    duration);
            toast.show();
        }

        @Override
        protected void onPostExecute(String html) {
            progress.dismiss();

            Context context = BrowseListActivity.this;
            Intent stopViewer = new Intent(context, StopActivity.class);
            stopViewer.setData(Uri.parse(html + ""));
            context.startActivity(stopViewer);

        }

    }

Answer 1

你做错的一件事是在错误之后继续执行doInBackground，这使得无法继续有意义地继续。例如：

try {
    response = client.execute(request);
} catch (ClientProtocolException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
} catch (IOException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
}

如果这引发异常，response将成为null，并且没有必要继续前进。您将在下一个代码块中生成NullPointerException。这不会是致命的，因为你正在捕捉那里的所有例外。不过，这种模式会重复，而且你没有抓住所有例外情况。

您应该提前退出，返回null作为String结果。然后，您可以在null中测试onPostExecute，并让用户以优雅的方式了解所发生的事情。

AsyncTask doInBackground有时仅返回nullpointerexception

1 个答案: