Kotlin ArrayAdapter Error: None of the following f

I am new to Kotlin for Android development. While following along a tutorial project, I needed to use ArrayAdapter with a custom class. Building the project failed with error.

The MainActivity.kt class throwing the error:

    class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)
    }

    val dm = DataManager()
    val adapterCourses = ArrayAdapter<CourseInfo>(
        context = this,
        android.R.layout.simple_spinner_item,
        dm.courses.values.toList()
    )

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        // Inflate the menu; this adds items to the action bar if it is present.
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        return when (item.itemId) {
            R.id.action_settings -> true
            else -> super.onOptionsItemSelected(item)
        }
    }
}

Error:

None of the following functions can be called with the arguments supplied:
public constructor ArrayAdapter<T : Any!>(@RecentlyNonNull p0: Context!, p1: Int) defined in android.widget.ArrayAdapter
public constructor ArrayAdapter<T : Any!>(@RecentlyNonNull p0: Context!, p1: Int, @RecentlyNonNull p2: Array<(out) CourseInfo!>!) defined in android.widget.ArrayAdapter
public constructor ArrayAdapter<T : Any!>(@RecentlyNonNull p0: Context!, p1: Int, p2: Int) defined in android.widget.ArrayAdapter
public constructor ArrayAdapter<T : Any!>(@RecentlyNonNull p0: Context!, p1: Int, p2: Int, @RecentlyNonNull p3: Array<(out) CourseInfo!>!) defined in android.widget.ArrayAdapter
public constructor ArrayAdapter<T : Any!>(@RecentlyNonNull p0: Context!, p1: Int, p2: Int, @RecentlyNonNull p3: (Mutable)List<CourseInfo!>!) defined in android.widget.ArrayAdapter
public constructor ArrayAdapter<T : Any!>(@RecentlyNonNull p0: Context!, p1: Int, @RecentlyNonNull p2: (Mutable)List<CourseInfo!>!) defined in android.widget.ArrayAdapter

The CourseInfo Class:

class CourseInfo (val courseId: String, val title: String)

The DataManager Class:

class DataManager {
    val courses = HashMap<String, CourseInfo>()
    val notes = ArrayList<NoteInfo>()

    init {
        initializeCourses()
    }

    private fun initializeCourses () {
        var course = CourseInfo(courseId = "android_intent", title = "Android programming with intent.")
        this.courses.set(course.courseId, course)

        course = CourseInfo(courseId = "android_async", title = "Android Async Programming and Services.")
        courses.set(course.courseId, course)

        course = CourseInfo(courseId = "java_lang", title = "Java Fundamentals: The Java Language.")
        courses.set(course.courseId, course)

        course = CourseInfo(courseId = "java_core", title = "Java Fundamentals: The Core Platforms.")
        courses.set(course.courseId, course)
    }
}

回答1:

Named arguments are not allowed for non-kotlin functions.

The problem is since you are invoking java ArrayAdapter constructor in kotlin file. you won't be able to provide argument label to it.

so following simple correction would resolve the issue.(Notice here, I removed context label in first argument.)

val adapterCourses = ArrayAdapter<CourseInfo>(this,
            android.R.layout.simple_spinner_item,
            dm.courses.values.toList())

回答2:

Use Below Code

val courseList:List<CourseInfo>= dm.courses.values.toList()
val adapterCourses = ArrayAdapter<CourseInfo>(this,android.R.layout.simple_spinner_item,courseList)