Kotlin:For循环必须具有迭代器方法-这是一个错误吗? [英] Kotlin: For-loop must have an iterator method - is this a bug?

问题描述

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()
}

这会给我错误:

For-loop范围必须具有'iterator()'方法

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

我在这里想念东西吗?

推荐答案

您的ArrayList是可为空的类型.因此，您必须解决此问题.有几种选择:

Your ArrayList is of nullable type. So, you have to resolve this. There are several options:

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

或

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

    }
}

或者您可以返回一个空列表

or you can just return an empty list

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

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