如何在Kotlin中使方法param可变

这里有两个问题.

First, you are mistakenly assuming that modifying view in Java does anything outside of the current function scope. It does not. You setting that parameter to a new value affects nothing outside of the local function scope.

View getView(int i, View view, ViewGroup parent) {
   // modify view here does nothing to the original caller reference to view
   // but returning a view does do something
}

接下来，在Kotlin中，所有参数都是final(JVM修饰符，与Java中的final修饰符相同).此代码的Kotlin if语句版本为:

fun getView(i: Int, view: View?, parent: ViewGroup): View {
   return if (view == null) {
       val tempView = View.inflate(context, R.layout.item_spinner, parent)
       tempView.tag(Holder(tempView))
       tempView
   } else { 
       (view.tag as Holder).title.text = getItem(i)
       view
   }
}

or avoiding the new local variable:

fun getView(i: Int, view: View?, parent: ViewGroup): View {
   return if (view == null) {
       View.inflate(context, R.layout.item_spinner, parent).apply {
           tag(Holder(this)) // this is now the new view
       }
   } else { 
       view.apply { (tag as Holder).title.text = getItem(i) }
   }
}

or

fun getView(i: Int, view: View?, parent: ViewGroup): View {
   if (view == null) {
       val tempView = View.inflate(context, R.layout.item_spinner, parent)
       tempView.tag(Holder(tempView))
       return tempView
   } 

   (view.tag as Holder).title.text = getItem(i)
   return view
}

or using the ?. and ?: null operators combined with apply():

fun getView(i: Int, view: View?, parent: ViewGroup): View {
    return view?.apply { 
                (tag as Holder).title.text = getItem(i) 
           } ?: View.inflate(context, R.layout.item_spinner, parent).apply {
                     tag(Holder(this))
                }
}

And there are another 10 variations, but you can experiment to see what you like.

使用相同的名称对变量进行阴影处理被认为是不太好的做法(但被允许)，这就是为什么它是一个编译器警告.为什么上面的变量名从view变为tempView