我是Android开发的新手，在教程中看到了这段代码
class MainActivity : AppCompatActivity() {
private val newNumber by lazy(LazyThreadSafetyMode.NONE) {
findViewById<EditText>(R.id.newNumber) }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val listener = View.OnClickListener {v ->
val b = v as Button
newNumber.append(v.text)
}
}
}
我试图理解“ as”运算符，因此编写了以下代码：
fun main(args: Array<String>) {
open class View {
fun a() {
println("This is the View method")
}
}
open class TextView: View() {
fun b() {
println("This is the TextView method")
}
}
open class Button: TextView() {
fun c() { …当我尝试从一个方法修改它时,我定义了一个名为notes的变量,android studio说
val无法重新分配
但是,如果我像这样访问变量,我可以修改它:this.notes.
class NoteAdapter(var context : Context) : RecyclerView.Adapter<NoteViewHolder>(){
private var notes = emptyList<Note>()
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): NoteViewHolder {
var itemView = LayoutInflater.from(context).inflate(R.layout.note_item, parent, false)
return NoteViewHolder(itemView)
}
override fun getItemCount(): Int {
return notes.size
}
fun setNotes(notes: List<Note>) {
this.notes = notes
notifyDataSetChanged()
}
为什么会这样？
我来自Javascript背景,所以请原谅我的无知.