我有以下代码:

public fun findSomeLikeThis(): ArrayList<T>? {
    val result = Db4o.objectContainer()!!.queryByExample<T>(this as T) as Collection<T>
    if (result == null) return null
    return ArrayList(result)
}

如果我这样称呼:

var list : ArrayList<Person>? = p1.findSomeLikeThis()

for (p2 in list) {
    p2.delete()
    p2.commit()
}

它会给我错误:

For-loop range must have an 'iterator()' method

我错过了什么吗？

最佳答案

您的 ArrayList 是可为空的类型。所以，你必须解决这个问题。有几种选择:

for (p2 in list.orEmpty()) { ... }

或

 list?.let {
    for (p2 in it) {

    }
}

或者你可以只返回一个空列表

public fun findSomeLikeThis(): List<T> //Do you need mutable ArrayList here?
    = (Db4o.objectContainer()!!.queryByExample<T>(this as T) as Collection<T>)?.toList().orEmpty()

https://stackoverflow.com/questions/29201182/