为什么 Android 设备上不显示工作日对象列表？Kotlin 列表视图

Question

我正在编写我的第一个Android规划应用程序。 我有一个导航抽屉和一个WeekListFragment。在片段中，我创建了一个 WeekDay 对象数组，并尝试通过 WeekAdapter 显示它们。但是当我运行 Android 模拟器时，尽管片段打开，但什么都不会显示。你能解释一下我应该怎么做吗？

下面是此片段的代码：

package itshpit.com.myapplication
import android.content.Context
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import android.widget.ImageView
import android.widget.TextView
import androidx.fragment.app.Fragment
import itshpit.com.myapplication.classes.WeekDay
class WeekListFragment() : Fragment() {
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view: View? = inflater.inflate(R.layout.fragment_week, container, false)
(activity as MainActivity).supportActionBar!!.title = "Week"
val week: Array<String> = resources.getStringArray(R.array.week)
val weekList: ArrayList<WeekDay> = ArrayList()
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 1))
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 2))
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 3))
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 4))
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 5))
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 6))
weekList.add(WeekDay(text = "some Text", image = R.drawable.mon, id = 7))
val adapter = WeekAdapter((activity as MainActivity), weekList)
return view
}
class WeekAdapter(context: Context, val weekList: List<WeekDay>) : ArrayAdapter<WeekDay>(context, 0, weekList) {
private class ViewHolder(row: View?) {
var txtName: TextView
var ivImage: ImageView
init {
this.txtName = row?.findViewById(R.id.txtWeekDay) as TextView
this.ivImage = row.findViewById(R.id.imgWeekDay) as ImageView
}
}
override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
val view: View?
val viewHolder: ViewHolder
if (convertView == null) {
val layout = LayoutInflater.from(context)
view = layout.inflate(R.layout.week_item, parent, false)
viewHolder = ViewHolder(view)
view.tag = viewHolder
} else {
view = convertView
viewHolder = view.tag as ViewHolder
}
val weekDay: WeekDay = getItem(position) as WeekDay
viewHolder.txtName.text = weekDay.text
viewHolder.ivImage.setImageResource(weekDay.image)

return view as View
}
override fun getItemId(position: Int): Long {
return weekList[position].id
}
override fun getItem(position: Int): WeekDay? {
return weekList.get(position)
}
override fun getCount(): Int {
return 7
}
}
}

平日课程代码如下：

data class WeekDay(var id: Long = -1,
var date: Date? = null,
var text: String,
var image: Int
) {}

"fragment_week.xml"文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
tools:context=".WeekListFragment">
<ListView
android:id="@+id/weekList"
android:layout_width="match_parent"
android:layout_height="match_parent">
</ListView>
</RelativeLayout>

Answer 1

您从未将适配器分配给列表视图。

首先，您需要对列表视图的引用。把它放在你的回程线之前：

val weekList: ListView = findViewById(R.id.weekList)

请注意，如果使用 Kotlin Android 扩展(默认情况下，新的 Android 项目会这样做(，则无需执行此步骤。Kotlin Android 扩展程序会自动为您的视图 ID 生成属性。

然后调用删除您现有的val adapter = ...行并执行以下操作：

weekList.adapter = WeekAdapter(context, weekList)

请注意，我将(activity as MainActivity)更改为context。这是因为您的适配器只在其构造函数中请求context。