执行网络进程时无法在未调用Looper.prepare（）的线程内创建处理程序

Question

I am attempting to run a networking process in the background of my app, to send an email. Since it's a networking task, it has to be run on a separate thread in the background. However, I am unable to get the thread to execute properly. To start a new thread, I just create one, and run it using Thread.start(),

    new Thread(){


        public void run(){
                            Mail mail = new Mail();
            mail.setFrom("someone@example.com");
            mail.setTo("someone@to.com");
            mail.setSubject("Hello");
            mail.setMessage("World");

            try
            {
                if (mail.send())
                {
                    Toast.makeText(getActivity(),
                            "Email Sent Successfully", Toast.LENGTH_LONG)
                            .show();
                }

                else
                    Toast.makeText(getActivity(),
                            "Email Not Sent", Toast.LENGTH_LONG).show();

            }
            catch (Exception e)
            {
                Log.i("Debug","Could not send email - " + e);
                Log.i("Debug",e.getStackTrace().toString());
            }


        }
    }.start();

However, I always get the error Can't create handler inside thread that has not called Looper.prepare()

I tried a few other things, trying to pass Looper.getMainLooper() to the thread, via a Handler with Runnable, but it gives me the same error. I have also tried to use AsyncTask but it seems that since this is not a UI operation, use of AsyncTask is incorrect (plus, it also gives me the same error).

Here's my stacktrace

 03-01 16:14:43.305: I/GreenBook(4454): java.lang.RuntimeException: Can't create handler inside     thread that has not called Looper.prepare()
03-01 16:14:43.305: I/GreenBook(4454):  at android.os.Handler.<init>(Handler.java:121)
03-01 16:14:43.305: I/GreenBook(4454):  at android.widget.Toast$TN.<init>(Toast.java:361)
03-01 16:14:43.305: I/GreenBook(4454):  at android.widget.Toast.<init>(Toast.java:97)
03-01 16:14:43.305: I/GreenBook(4454):  at android.widget.Toast.makeText(Toast.java:254)
03-01 16:14:43.305: I/GreenBook(4454):  at     com.stacksmashers.greenbook.RegisterActivity$10.run(RegisterActivity.java:688)

Answer 1

Can't create handler inside thread that has not called Looper.prepare()

That is because you are trying to show a Toast .

I have also tried to use AsyncTask but it seems that since this is not a UI operation, use of AsyncTask is incorrect

A Toast would be considered by most developers to be part of the UI.

plus, it also gives me the same error

Perhaps you are trying to show the Toast from doInBackground() . Show your Toast in onPostExecute() (or onProgressUpdate() , if you elect to call publishProgress() ).