如何使用Kotlin在Android Studio中引用TimerPicker

Question

When this program runs on the emulator it works, however, when I run it on my phone the timePicker is referenced as null.

An emulator running API 26 can run it fine, however, at API 28 it does not work. So I think It might be something with API 28 (which also is what my phone runs)

class MainActivity : AppCompatActivity() {

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

        val picker = findViewById<TimePicker>(R.id.timePicker)

        val t = picker == null // Is true on phone and is false on emulator

        Toast.makeText(this@MainActivity, t.toString(), Toast.LENGTH_LONG).show()
        //picker.setIs24HourView(true)

        val activity = findViewById<EditText>(R.id.activityName)
        val mCallApiButton = findViewById<Button>(R.id.submit)
        mCallApiButton?.setOnClickListener{
            val time = GetTime(picker)

            PostActivity(time, activity.text.toString()) // Function that does other stuff
        }
    }
}

I need to reference the timePicker so that I can set it to 24H.

Here is a look at the layout file:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">
    <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent" app:layout_constraintTop_toTopOf="parent">
        <TimePicker android:id="@+id/timePicker"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:timePickerMode="clock"/>
        <EditText
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:ems="10"
                android:id="@+id/activityName"
                android:singleLine="true" android:hint="Activity" android:textSize="18sp"
                android:textAlignment="center" android:autofillHints="Activity"/>
        <Button
                android:text="Submit"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" android:id="@+id/submit"/>
    </LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

Screenshot of the emulator: (Which is how it should look)

Screenshot of the phone:

Answer 1

This is because I use API 28 and not 27 and under. The answer can found here: https://github.com/xamarin/Xamarin.Forms/issues/5159