android计数器-Kotlin

class MainActivity : AppCompatActivity() {

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

    fun incrementCount(view: View) {
        handleCounter(1)
    }

    fun decrementCount(view: View) {
        handleCounter(-1)
    }

    private fun handleCounter(sum: Int) {
        val countText: TextView = findViewById(R.id.count);
        countText.text = (sum + countText.text.toString().toInt()).toString()
        Log.d("count:", (countText.text as? String).toString())
        //as? -> 如果不能toString 返回null ， 多加一个toString 配合 as? 防止应用崩溃
    }

}

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/count"
        android:autoLink="all"
        android:gravity="center_horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/count"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_increment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginHorizontal="10dp"
        android:text="@string/increment"
        android:onClick="incrementCount"
        app:layout_constraintBottom_toTopOf="@+id/btn_decrement"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_decrement"
        android:layout_width="match_parent"
        android:layout_marginHorizontal="10dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="@string/decrement"
        android:onClick="decrementCount"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btn_increment" />
</LinearLayout>