当 kotlin 中的表达式无法按预期工作时

Question

我想知道是否有人可以帮助我解决代表 When Expression 特定代码块的问题？

我有 2 个活动要连接：

第一个 activity 是 MainActivity.kt，第二个 activity 是 Main2Activity.kt，在第二个 activity 中，我遇到了应用特定表达式时的问题Main2Activity class 中的代码块因为我想在 MainActivity class 中单击图像时在 Main2Activity class 中传递特定适配器，就像在第一个 activity [=74 中单击图像 b 时传递 ADAPTER_TYPE_2 =]，它的主要问题总是在 Main2Activity class

中应用第一个代码块

注意：第一个 activity 使用 GridView，第二个 activity 使用 ListView，我在 Main2Activity.kt 中有 2 个适配器，我正在使用 enum 由第二个 activity

中的每个适配器组成

这是一个MainActivity.kt

class MainActivity : AppCompatActivity() {

var adapter:FoodAdapter?=null
var listOfFoods =ArrayList<Food>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(layout.activity_main)


// load foods
listOfFoods.add(Food("Coffee","   Coffee preparation is", a))
listOfFoods.add(Food("Coffee","   Coffee preparation is", b))
listOfFoods.add(Food("Coffee","   Coffee preparation is", c))
listOfFoods.add(Food("Coffee","   Coffee preparation is", d))

adapter= FoodAdapter(this,listOfFoods)

gvListFood.adapter =adapter

}


class  FoodAdapter: BaseAdapter {
var listOfFood= ArrayList<Food>()
var context: Context?=null
constructor(context:Context,listOfFood:ArrayList<Food>):super(){
    this.context=context
    this.listOfFood=listOfFood
}
override fun getView(p0: Int, p1: View?, p2: ViewGroup?): View? {
    val food = this.listOfFood[p0]
    var inflator = context!!.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
    var foodView= inflator.inflate(layout.food_ticket,null)
    foodView.ivFoodImage.setImageResource(food.image!!)
    foodView.ivFoodImage.setOnClickListener {


        val intent = Intent(context, Main2Activity::class.java)

        when (foodView) {
            foodView.ivFoodImage.also { a } ->
                intent.putExtra(Main2Activity.EXTRA_ADAPTER_MODE, AdapterType.ADAPTER_TYPE_1.ordinal) {

                    intent.putExtra("name", food.name!!)
                    intent.putExtra("des", food.des!!)
                    intent.putExtra("image", food.image!!)
                    context!!.startActivity(intent)
                }

            foodView.ivFoodImage.also { b } ->
                intent.putExtra(Main2Activity.EXTRA_ADAPTER_MODE, AdapterType.ADAPTER_TYPE_2.ordinal) {

                   intent.putExtra("name", food.name!!)
                   intent.putExtra("des", food.des!!)
                   intent.putExtra("image", food.image!!)
                   context!!.startActivity(intent)
            }
        }

    }
    return foodView
}

override fun getItem(p0: Int): Any {
    return listOfFood[p0]
}

override fun getItemId(p0: Int): Long {
    return p0.toLong()
}

override fun getCount(): Int {

    return listOfFood.size
}

}
}

这是第一个food_ticket.xmlactivity

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="63pt"
android:layout_height="wrap_content"
android:background="@color/gray"
android:orientation="vertical"
android:padding="3pt">

<LinearLayout
android:gravity="center"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/background"
android:orientation="vertical">

<ImageView
    android:id="@+id/ivFoodImage"
    android:layout_width="50pt"
    android:layout_height="50pt"
    app:srcCompat="@drawable/c" />

<TextView
    android:id="@+id/tvName"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"
    android:text="Coffe"
    android:textSize="20sp" />
</LinearLayout>
</LinearLayout>

这是一个Main2Activity.kt

class Main2Activity : AppCompatActivity() {
companion object {
    val EXTRA_ADAPTER_MODE = "extra_adapter_mode"

}

    var adapter1: FoodAdapter1?= null
    var adapter2: FoodAdapter2? = null
    var listOfFoods2 = ArrayList<Food>()
    var listOfFoods3 = ArrayList<Food>()
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(activity_main2)


    val bundle = intent.extras
    val adapterTypeOrdinal = intent.getIntExtra(EXTRA_ADAPTER_MODE, 0) // 0 is the default value
    val type = AdapterType.fromOrdinal(ordinal = adapterTypeOrdinal)


    val name = bundle.getString("name")
    val des = bundle.getString("des")
    val image = bundle.getInt("image")



    ivFoodImage2?.let {
        it.setImageResource(image)
    }

    tvName2?.let {
        it.text = name
    }

    tvDes2?.let {
        it.text = des
    }


    // load foods2
    listOfFoods2.add(Food("Coffee", "   Coffee1 preparation is", R.drawable.a))
    listOfFoods2.add(Food("Coffee", "   Coffee2 preparation is", R.drawable.b))



    // load foods3
    listOfFoods3.add(Food("Coffee", "   Coffee3 preparation is", R.drawable.c))
    listOfFoods3.add(Food("Coffee", "   Coffee4 preparation is", R.drawable.d))

     //var ADAPTER_TYPE_1 = adapter1
    //var ADAPTER_TYPE_2 = adapter2

    lvFoods2.adapter = when (type) {
        AdapterType.ADAPTER_TYPE_1-> FoodAdapter1(listOfFoods2, this)
        AdapterType.ADAPTER_TYPE_2-> FoodAdapter2(listOfFoods3, this)
        else -> lvFoods2.adapter
    }
}



class FoodAdapter1 : BaseAdapter{
    var context: Context? = null
    var listOfFoodsLocal2 = ArrayList<Food>()

    constructor(listOfFoods2: ArrayList<Food>, context: Context) : super() {
        this.listOfFoodsLocal2 = listOfFoods2
        this.context = context
    }

    override fun getView(p0: Int, foodView: View?, p2: ViewGroup?): View {
        val food = this.listOfFoodsLocal2[p0]
        var inflator = context!!.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
        val foodView = inflator.inflate(food_ticket2, null)



        foodView.ivFoodImage2?.let {
            it.setImageResource(food.image!!)
                 }
        foodView.tvName2?.let {

            it.text = food.name!!
        }
        foodView.tvDes2?.let {
            it.text = food.des!!
        }

        foodView.ivFoodImage2.setOnClickListener {

            //move to next
            val intent = Intent(context, FoodDetails::class.java)
            intent.putExtra("name", food.name!!)
            intent.putExtra("des", food.des!!)
            intent.putExtra("image", food.image!!)

            context!!.startActivity(intent)

        }
        return foodView

    }


    override fun getItem(p0: Int): Any {
        return listOfFoodsLocal2[p0]
    }

    override fun getItemId(p0: Int): Long {
        return p0.toLong()
    }

    override fun getCount(): Int {
        return listOfFoodsLocal2.size
    }

}

class FoodAdapter2 : BaseAdapter {
    var context: Context? = null
    var listOfFoodsLocal3 = ArrayList<Food>()

    constructor(listOfFoods3: ArrayList<Food>, context: Context) : super() {
        this.listOfFoodsLocal3 = listOfFoods3
        this.context = context
    }

    override fun getView(p0: Int, p1: View?, p2: ViewGroup?): View {
        val food = this.listOfFoodsLocal3[p0]
        var inflator = context!!.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
        val foodView = inflator.inflate(food_ticket2, null)


            foodView.ivFoodImage2?.let {
                it.setImageResource(food.image!!)
            }
            foodView.tvName2?.let {
                it.text = food.name!!
            }
            foodView.tvDes2?.let {
                it.text = food.des!!
            }




        foodView.ivFoodImage2.setOnClickListener {

            //move to next
            val intent = Intent(context, FoodDetails::class.java)
            intent.putExtra("name", food.name!!)
            intent.putExtra("des", food.des!!)
            intent.putExtra("image", food.image!!)

            context!!.startActivity(intent)

        }
        return foodView

    }


    override fun getItem(p0: Int): Any {
        return listOfFoodsLocal3[p0]
    }

    override fun getItemId(p0: Int): Long {
        return p0.toLong()
    }

    override fun getCount(): Int {
        return listOfFoodsLocal3.size
    }

}
}

activity_main2.xml 第二个 activity

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/gray"
android:orientation="vertical"
tools:context="com.marzadmz.startup.Main2Activity">

<ListView
android:id="@+id/lvFoods2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/gray" />
</LinearLayout>

AdapterType.kt 用于枚举 class

enum class AdapterType {
ADAPTER_TYPE_1,
ADAPTER_TYPE_2;



    companion object {
        fun fromOrdinal(ordinal: Int): AdapterType? {
            return AdapterType.values().firstOrNull { it.ordinal == ordinal }
        }
    }
}

null error image 2nd picture

Answer 1

实施已关闭

var ADAPTER_TYPE_1 = adapter1
var ADAPTER_TYPE_2 = adapter2

lvFoods2.adapter = when (lvFoods2.adapter) {
    ADAPTER_TYPE_1 -> FoodAdapter1(listOfFoods2, this).also { ADAPTER_TYPE_1 = it }
    ADAPTER_TYPE_2  -> FoodAdapter2(listOfFoods3, this).also { ADAPTER_TYPE_2 = it }
    else -> lvFoods2.adapter
}

adapter1 变量和 lvFoods2.adapter 一样为空。根据我对你的代码的理解，它应该是这样的：

lvFoods2.adapter = when (type) {
    ADAPTER_TYPE_1 -> FoodAdapter1(listOfFoods2, this)
    ADAPTER_TYPE_2  -> FoodAdapter2(listOfFoods3, this)
    else -> lvFoods2.adapter
}

当 kotlin 中的表达式无法按预期工作时

When expression in kotlin not working as expected

android

android-adapter

android-activity

kotlin