java.lang.RuntimeException: Can't create handler inside thread that has not calledLooper.prepare()

Looper.prepare();

Toast.makeText(getApplicationContext(), "test", Toast.LENGTH_LONG).show();

Looper.loop();

    public void show() {

      ...

        service.enqueueToast(pkg, tn, mDuration);   //把这个toast插入到一个队列里面

        ...

    }

public static final void prepare() {

        if (sThreadLocal.get() != null) {

            throw new RuntimeException("Only one Looper may be created per thread");

        }

       sThreadLocal.set(new Looper());  //在当前线程中创建一个Looper

    }

private Looper() {

        mQueue = new MessageQueue();  //关键在这，创建Looper都干了什么。 其实是创建了消息队列

        mRun = true;

        mThread = Thread.currentThread();

    }

    public Toast(Context context) {

        mContext = context;

        mTN = new TN();

        mTN.mY = context.getResources().getDimensionPixelSize(

                com.android.internal.R.dimen.toast_y_offset);

    }

    private static class TN extends ITransientNotification.Stub {

        ……

        final Handler mHandler = new Handler();    

        ……

    }

   /**

     * Default constructor associates this handler with the queue for the

     * current thread.

     *

     * If there isn't one, this handler won't be able to receive messages.

     */

    public Handler() {

        if (FIND_POTENTIAL_LEAKS) {

            final Class<? extends Handler> klass = getClass();

            if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&

                    (klass.getModifiers() & Modifier.STATIC) == 0) {

                Log.w(TAG, "The following Handler class should be static or leaks might occur: " +

                    klass.getCanonicalName());

            }

        }

        mLooper = Looper.myLooper();

        if (mLooper == null) {

            throw new RuntimeException(

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

        }

        mQueue = mLooper.mQueue;

        mCallback = null;

    }