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

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

问题描述：
开启一个子线程，使用handler去提醒ui线程，使用了Toast。贴出代码来

 Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
//            super.handleMessage(msg);
            switch (msg.what) {
                case StrUtil.FORGET_PWD_SUCCEED:
//                    dismissDialog();
                    Toast.makeText(PasswordBackActivity.this,"密码成功找回",Toast.LENGTH_SHORT).show();
                    break;
                case StrUtil.FORGET_PWD_FAILED:
                    dismissDialog();
                    Toast.makeText(PasswordBackActivity.this,"网络错误，密码未找回",Toast.LENGTH_SHORT).show();
                    break;
                default:
                    break;
            }
        }
    };

出现错误的地方很奇怪，是

Toast.makeText(PasswordBackActivity.this,"密码成功找回",Toast.LENGTH_SHORT).show();

而下面一行

Toast.makeText(PasswordBackActivity.this,"网络错误，密码未找回",Toast.LENGTH_SHORT).show();

却不会出错。只有上面的会出错，下面的正常运行。
不知道是怎么回事，但我的解决方法是：

......
......
message.what = StrUtil.FORGET_PWD_SUCCEED;
handler.handleMessage(message);
Looper.prepare();
Toast.makeText(PasswordBackActivity.this,"密码成功找回",Toast.LENGTH_SHORT).show();
Looper.loop();
......
......

将Toast移到子线程中，并且在Toast上下使用Looper包括起来。

Looper.prepare();
Looper.loop();

问题解决，没报错