请问大家都是怎么读取idfa的，官网的事例报错

首先我在manifest里面勾选了使用广告标识，并且手机没有限制读取idfa，然后使用下面的代码读取

var ASIdentifierManager = plus.ios.importClass("ASIdentifierManager");      
var sharedManager = ASIdentifierManager.sharedManager();    
var idfa = '';    
if (sharedManager.isAdvertisingTrackingEnabled()){      
    var advertisingIdentifier = sharedManager.advertisingIdentifier();      
    idfa = plus.ios.invoke(advertisingIdentifier,"UUIDString");      
}    
console.log('idfa = '+idfa);  

结果报错，ASIdentifierManager为null，

TypeError: null is not an object (evaluating 'ASIdentifierManager.sharedManager') at App.vue:65 __ERROR