类com.test.test.LibraryBook没有定义无参数构造函数

Question

我得到以下错误Class com.test.test.LibraryBook does not define a no-argument constructor

这是我的代码：

override fun onDataChange(dataSnapshot: DataSnapshot) {
if (dataSnapshot.exists()) {
if (dataSnapshot.children.count() > 0) {
for (eventSnapshot in dataSnapshot.children) {
val lb = eventSnapshot.getValue(LibraryBook::class.java)
lb?.let {
val id = lb.id
val title = lb.title
val image = lb.image

这是LibraryBook数据类

@IgnoreExtraProperties
data class LibraryBook(val id: String,
val title: String = "",
var image: String = "",
var subtitle: String = "",
var author: String = "",
var desc: String = "",
var uploadDate: Long = 0,
var starCount: Long = 0)

我做错了什么？

Answer 1

Kotlin没有为LibraryBook生成无参数构造函数，因为它仍然有一个必需的id参数。您必须使用一些默认值使该参数可选，就像其他参数一样。