安卓系统，代码如下 ，当前连接，距WIFI点远近，手机显示强弱环境，getConnectedWifi返回的wifi.signalStrength都为99是怎么回事?

getConnectedWifi:function(){

var that = this

that.stopWifi();

that.startWifi();

wx.getConnectedWifi({

success: function(res){

console.log(res);

that.setData({ message2: res.wifi.SSID});

that.setData({ message3: res.wifi.signalStrength});

},

fail:function(err){

console.log(err);

that.setData({ message2: err.errCode});  //‘失败’‘失败’

}

})

},