tp5框架ajax登陆功能,TP5下CMF5里的ajax处理代码

前端传参数到后台controller，后台里应该怎么接收传过来的参数，并且返回的list应如何return?

如下示例：

$.ajax({

url:"{:url('myapp/city/allDistricts')}",

data: {cityId:126},

type: 'post',

dataType: "json",

success: function (data) {

var cityList = eval("(" + data + ")");

alert(cityList.length);

},

complete:function() {

}

});

后台

public function allDistricts()

{

//$cityId = $this->request->param('cityId', 0, 'intval');

//$cityId = Request::instance()->post('cityId');

$cityId=126;

$cityModel = new CityModel();

$field = 'id,city_name';

$where = [

'parent_id' => $cityId

];

$lists = $cityModel->field($field)->where($where)

->order('list_order','desc')->select();

//$this->ajaxReturn($lists);

//return json_encode($lists);

return json($lists);

}

接收参数与return 的代码尝试了多种，前端就是死活没反应，百度了一下，发现TP5与TP3对ajax的处理已经不同了，有大神能指条生路吗？