Android:AsyncTask onPreExecute() 方法未在 UI 线程中执行

Question

我有一个 AsyncTask 从线程执行。在 onPreExecute() 方法中，我想更改一些 TextView，但出现以下错误(回顾):

05-07 11:53:02.039: E/AndroidRuntime(7062): FATAL EXCEPTION: processBarcodeThread
05-07 11:53:02.039: E/AndroidRuntime(7062): android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
.....
05-07 11:53:02.039: E/AndroidRuntime(7062):     at android.widget.TextView.setText(TextView.java:2573)
05-07 11:53:02.039: E/AndroidRuntime(7062):     at it.mbm.droid.activity.fragment.LabelAnagFragment$ReadFromServerTask.onPreExecute(LabelAnagFragment.java:301)
05-07 11:53:02.039: E/AndroidRuntime(7062):     at android.os.AsyncTask.execute(AsyncTask.java:391)

这意味着 onPreExecute() 不在 UI 线程上执行，但根据 Android 文档:

onPreExecute(), invoked on the UI thread before the task is executed. This step is normally used to setup the task, for instance by showing a progress bar in the user interface.

那么，我哪里做错了？

Answer 1

您似乎是从后台线程在 AsyncTask 上调用 execute()。如果您阅读了 AsyncTask 的文档，您会发现这是不受支持的:

There are a few threading rules that must be followed for this class to work properly:

• The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN.
• The task instance must be created on the UI thread.
• execute(Params...) must be invoked on the UI thread. ...

因此，请更改代码以从主应用程序线程调用 AsyncTask 上的 execute()。