在快速建立完預設的Fragment後
我們就能把Fragment編入Activity中

但是我的Fragment同樣擁有自己的layout
於是呢和Activity不同的是
我不會在onCreate()調用回去
而是在onCreateView(),return 我們這次編排的layout

override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_main, container, false)
        }

當中的R.layout.fragment_main
就是我們快速建立Fragment時產生的Layout

編排MainActivity的Layout

利用到我們前幾篇介紹的ConstraintLayout去編排
設置一個區塊放置我們的Fragment

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_marginTop="50dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello MainActivity!"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/fragment"
        android:layout_width="match_parent"
        android:layout_height="500dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        android:background="@color/colorAccent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

編寫MainActivity.kt

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.d("Activity","onCreate")
        
        val newFragment = MainFragment()
        val transaction = supportFragmentManager.beginTransaction()
        transaction.replace(R.id.fragment, newFragment)
        transaction.addToBackStack(null)
        transaction.commit()

}