Question

即使我把它扔进AsyncTask的DoInBackground方法，我仍然会得到一个CalledFromWrongThreadException！谁能告诉我为什么以及如何解决它？

/**
     * Recognizes key words in responseTexts and runs the appropriate function
     * @param responseText
     */
    private void responseHandler(String responseText) {
        if(responseText.startsWith("Notes", 0)) {
            notes.add(responseText);
            new DownloadFilesTask().execute("WriteInternal" , null, null);
        }
    }

这是我的AsyncTask类

private class DownloadFilesTask extends AsyncTask<String, Void, String> {
    protected String doInBackground(String... command) {
    if(command[0].equals("WriteInternal") {
        //write to internal storage
    FileOutputStream fOut = null;
    OutputStreamWriter osw = null;
    try{
        fOut = openFileOutput("notes.txt", Context.MODE_PRIVATE);
        osw = new OutputStreamWriter(fOut);
        for (int i = 0; i < notes.size(); i++){
            osw.write(notes.get(i) + "\n");
        }
        osw.close();
        fOut.close();
    } catch(Exception e) {
        e.printStackTrace(System.err);
    }

    notesListView.setAdapter(arrayAdapter);  //refreshes the listView

       }
else {
        sendCommand(command[0]);
        return null;
}
    }

    protected void onProgressUpdate(Void... progress) {}
    protected void onPostExecute(String result) {}
}

这是我得到的堆栈跟踪：

05-22 15:14:20.370: E/AndroidRuntime(11730): FATAL EXCEPTION: AsyncTask #2
05-22 15:14:20.370: E/AndroidRuntime(11730): java.lang.RuntimeException: An error occured while executing doInBackground()
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.os.AsyncTask$3.done(AsyncTask.java:278)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.lang.Thread.run(Thread.java:856)
05-22 15:14:20.370: E/AndroidRuntime(11730): Caused by: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:4039)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.view.ViewRootImpl.invalidateChild(ViewRootImpl.java:722)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.view.ViewRootImpl.invalidateChildInParent(ViewRootImpl.java:771)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.view.ViewGroup.invalidateChild(ViewGroup.java:4005)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.view.View.invalidate(View.java:8576)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.view.View.invalidate(View.java:8527)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.widget.AbsListView.resetList(AbsListView.java:1734)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.widget.ListView.resetList(ListView.java:502)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.widget.ListView.setAdapter(ListView.java:442)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at com.nelson.jarvisclientics.Notes$DownloadFilesTask.doInBackground(Notes.java:281)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at com.nelson.jarvisclientics.Notes$DownloadFilesTask.doInBackground(Notes.java:1)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at android.os.AsyncTask$2.call(AsyncTask.java:264)
05-22 15:14:20.370: E/AndroidRuntime(11730):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
05-22 15:14:20.370: E/AndroidRuntime(11730):    ... 5 more

Answer 1

尝试使用runOnUIThread(new Runnable{/*code goes here*/}())

包装文件访问代码

Answer 2

您获得此异常的原因是您正在尝试更新AsyncTask的doInBackground（）方法中的UI。当您在此处为列表视图设置适配器时会发生这种情况：notesListView.setAdapter(arrayAdapter); //refreshes the listView

您应该将其移至onPostExecute。更新onPostExecute中的UI并在必要时显示任何错误消息。

另请注意，您也在后台调用handleCommand（）;确保这也不会更新UI！

Answer 3

您可以使用在UI线程上运行的onPostExecute ...这是使用asynctask的基础。

使用AsyncTask从错误的线程异常调用

3 个答案: