构造函数中的默认值在 Kotlin 中显示错误

Question

我的操作与 here 和 here 相同，但显示错误

这是我的班级，它的 primary constructor 没有 secondary constructor 没有 init 块。

class RowSubTShirtViewModel(private val subTShirtAdapter: SubTShirtAdapter, val context: TShirtActivity,
                            val tShirtBean: CommonItemBean, private val parentPosition: Int, private val position: Int) : BaseObservable(), TShirtActivity.setSelectionSubRow {}

创建像val vm=RowSubTShirtViewModel() 这样的对象会出错

• 创建抽象函数“RowSubTShirtViewModel”
• 创建函数“RowSubTShirtViewModel”
• 创建二级构造函数
• 没有为参数传递值

Answer 1

您需要将参数显式传递给主构造函数：

//init params
val subTShirtAdapter = ...
val context = ...
val tShirtBean = ...
val parentPosition = ...
val position = ...

//init viewModel
val vm = RowSubTShirtViewModel(subTShirtAdapter, context, tShirtBean, parentPosition, position)

除非您为参数分配默认值，例如：

class RowSubTShirtViewModel(private val subTShirtAdapter = YourAdapter(),...)

在你的情况下，你可以这样做：

class RowSubTShirtViewModel(val context: TShirtActivity, 
    private val subTShirtAdapter: SubTShirtAdapter, 
    val tShirtBean: CommonItemBean, 
    private val parentPosition: Int = 0, 
    private val position: Int = 0) : BaseObservable(), TShirtActivity.setSelectionSubRow {}

// and then create an instance
val vm = RowSubTShirtViewModel(yourContext, yourAdapter, yourShirtBean)

Answer 2

您没有在构造函数中使用default arguments。如果你喜欢使用，它应该看起来像

class RowSubTShirtViewModel(
    private val subTShirtAdapter: SubTShirtAdapter = defaultSubTShirtAdapter,
    val context: TShirtActivity = defultContext,
    val tShirtBean: CommonItemBean = defaultTShirtBean,
    private val parentPosition: Int = defaultParentPosition,
    private val position: Int = defaultPosition) : BaseObservable(), TShirtActivity.setSelectionSubRow {}