HarmonyOS getDrawableDescriptor获取指定名称的icon内容时报错,$r()不能接受动态变量吗

let onlineID = 'app.media.icon_' + deviceIcon + '_on'
let onlineID2 = 'app.media.icon_3_001_27_on'
try {
  getContext().resourceManager.getDrawableDescriptor($r(onlineID2 as string).id)
} catch (error) {
  let code = (error as BusinessError).code
  let message = (error as BusinessError).message
  isContainOn = false
}

这种情况是报错是入参有问题，$r()接受string，不明白为啥不行