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

                    Toast.makeText(context,"登录超时",Toast.LENGTH_SHORT).show();

                    Looper.loop();

这样子写就不会报错了；

但是他为什么报错？？？你是不是在子线程显示Toast了；来看一下Toast的源码：

    /**

     * Constructs an empty Toast object.  If looper is null, Looper.myLooper() is used.

     * @hide

     */

    public Toast(@NonNull Context context, @Nullable Looper looper) {

        mContext = context;

        mTN = new TN(context.getPackageName(), looper);

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

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

        mTN.mGravity = context.getResources().getInteger(

                com.android.internal.R.integer.config_toastDefaultGravity);

    }

TN : 就看最主要这一点吧！

  if (looper == null) {

                // Use Looper.myLooper() if looper is not specified.

                looper = Looper.myLooper();

                if (looper == null) {

                    throw new RuntimeException(

                            "Can't toast on a thread that has not called Looper.prepare()");

                }

            }

            mHandler = new Handler(looper, null) {

                @Override

                public void handleMessage(Message msg) {

                    switch (msg.what) {

                        case SHOW: {

                            IBinder token = (IBinder) msg.obj;

                            handleShow(token);

                            break;

                        }

                        case HIDE: {

                            handleHide();

                            // Don't do this in handleHide() because it is also invoked by

                            // handleShow()

                            mNextView = null;

                            break;

                        }

                        case CANCEL: {

                            handleHide();

                            // Don't do this in handleHide() because it is also invoked by

                            // handleShow()

                            mNextView = null;

                            try {

                                getService().cancelToast(mPackageName, TN.this);

                            } catch (RemoteException e) {

                            }

                            break;

                        }

                    }

                }

            };

报错的原因是因为你的looper == null ，myLooper也是null;

Toast的内部会创建Handler，而Handler又依赖于Looper；Looper不存在，自然会报错；

Android主线程会默认创建Looper，而子线程则不会默认创建Looper；所以我们需要手动去创建Looper并开启循环；