由于大量数据，AsyncTask 中的异常答案

【问题标题】：Exception in AsyncTask due to enormous number of data由于大量数据，AsyncTask 中的异常
【发布时间】：2012-10-04 21:11:29
【问题描述】：

我正在从我的 Android 应用程序连接到 Java 中的 RESTful Web 服务。我正在使用 AsyncTask 来获取数据。它适用于正常数量的数据。但是当我有大量数据时，Android 应用程序中会发生异常。我试图捕捉这个异常，但我不能：

private class LoadingDataFromServer extends AsyncTask<Void, Void, Void> {

        private boolean outOfMemory = false;

        @Override
        public void onPreExecute() {
            progress = ProgressDialog.show(main_activity, null,"Loading ...", true);
        }

        @Override
        protected void onPostExecute(Void result) {
            if(outOfMemory) {
                Toast.makeText(StatisticActivity.this, "Out of memory, select smaller criteria", Toast.LENGTH_SHORT).show();
                finish();
            }
            else
                setListView();
            try {
                progress.dismiss();
            } catch (Exception e) { }
        }

        @Override
        protected Void doInBackground(Void... params) {
            TextView txtProject = (TextView) main_activity.findViewById(R.id.project);
            txtProject.setBackgroundColor(Color.DKGRAY);
            txtProject.setText(project);

            TextView label = (TextView) main_activity.findViewById(R.id.label);
            label.setText(R.string.deliverable);
            try {
            loadStatistic();
            } catch (OutOfMemoryError e) {
                outOfMemory = true;
                progress.dismiss();
            } catch (RuntimeException e) {
                outOfMemory = true;
                progress.dismiss();
            } catch (Exception e) {
                outOfMemory = true;
                progress.dismiss();
            }
            return null;
        }
    }

这是我得到的错误：

10-14 22:24:10.952: ERROR/AndroidRuntime(4179): Uncaught handler: thread AsyncTask #3 exiting due to uncaught exception
10-14 22:24:10.962: ERROR/AndroidRuntime(4179): java.lang.RuntimeException: An error occured while executing doInBackground()
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.lang.Thread.run(Thread.java:1102)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at android.os.Handler.<init>(Handler.java:121)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at android.widget.Toast.<init>(Toast.java:68)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at android.widget.Toast.makeText(Toast.java:231)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at se.softwerk.timelog.statistic.StatisticActivity$LoadingDataFromServer.doInBackground(StatisticActivity.java:301)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at se.softwerk.timelog.statistic.StatisticActivity$LoadingDataFromServer.doInBackground(StatisticActivity.java:1)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-14 22:24:10.962: ERROR/AndroidRuntime(4179):     ... 4 more

异常发生在doInBackground，但我的异常处理不起作用。你能帮帮我吗？

【问题讨论】：

听起来异常告诉你到底出了什么问题：Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

标签： java android multithreading web-services android-asynctask

【解决方案1】：

您应该从onPreExecute()、onProgressUpdate(Progress... values) 或onPostExecute(Result result)（在主线程，即 UI 线程中运行）调用任何与 UI 相关的代码，并仅使用 doInBackground(Params... params) 执行 CPU 密集型操作。

在doInBackground(Params... params) 中调用publishProgress(Progress... values) 会将数据发送到onProgressUpdate(Progress... values)，您可以在其中使用它来更新UI。

【讨论】：