Android-如何用Kotlin簡易設定與監聽按鈕(Button)

想必各位大大從 Java 轉到 Kotlin 有極大的痛楚
此篇就以現在常遇到的狀況下做簡易的介紹

首先我們先把一般情況下的
先把頁面畫出來

1 . activity_button.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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">

    <Button
        android:id="@+id/buttonTest"
        android:layout_width="88dp"
        android:layout_height="48dp"
        android:layout_marginBottom="232dp"
        android:layout_marginEnd="148dp"
        android:layout_marginStart="148dp"
        android:layout_marginTop="231dp"
        android:text="我是按鈕"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

重點來了
以下是 Java 寫法 ：

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class ButtonJavaActivity extends AppCompatActivity implements View.OnClickListener {

    private Button btnTest;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnTest = findViewById(R.id.buttonTest);
        btnTest.setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.buttonTest:
                Toast.makeText(this, "Test", Toast.LENGTH_SHORT).show();
                break;
            default:
                break;
        }
    }
}

以下是 Kotlin 寫法 ：

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.view.View
import android.widget.Button
import android.widget.Toast

class ButtonActivity : AppCompatActivity(), View.OnClickListener {

    private lateinit var btnTest: Button;

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

        btnTest = findViewById(R.id.buttonTest);
        btnTest.setOnClickListener(this);
        
    }

    override fun onClick(v: View?) {
        when (v?.id) {
            R.id.buttonTest -> {
                Toast.makeText(this, "Test", Toast.LENGTH_SHORT).show();
            }
            else -> {

            }
        }
    }
}