Android,如何替换初始片段?

我创建这个片段并设置初始片段 FirstFragment ,如果不设置此初始片段,应用程序将崩溃。

<fragment
    android:id="@+id/fragment"
    android:name="com.app.FirstFragment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp" />

然后我使用这个函数来替换片段,这很好,除了 第一片段 ,此片段一直显示在屏幕上如何替换此碎片?

enum class FragmentType {
    SETTING, ACTIVITY, PROFILE, CONNECT, SCANNER
}
private fun changeFragmentTo(type: FragmentType) {
    val transaction = supportFragmentManager.beginTransaction()
    when(type) {
        FragmentType.SETTING -> {
            title = "SETTING"
            val f = SettingFragment()
            transaction.replace(R.id.fragment, f)
        }

        FragmentType.ACTIVITY -> {
            title = "ACTIVITY"
            val f = ActivityFragment()
            transaction.replace(R.id.fragment, f)
        }

        FragmentType.PROFILE -> {
            title = "PROFILE"
            val f = ProfileFragment()
            transaction.replace(R.id.fragment, f)
        }
        FragmentType.CONNECT -> {
            title = "CONNECT"
            val f = ConnectFragment()
            transaction.replace(R.id.fragment, f)
        }
        FragmentType.SCANNER -> {
            title = "SCANNER"
            val f = ScannerFragment()
            transaction.replace(R.id.fragment, f)
        }

    }
    transaction.addToBackStack(null)
    transaction.commit()
}