package com.example.myapplication2

import android.os.Bundle import com.google.android.material.snackbar.Snackbar import androidx.appcompat.app.AppCompatActivity import androidx.navigation.findNavController import androidx.navigation.ui.AppBarConfiguration import androidx.navigation.ui.navigateUp import androidx.navigation.ui.setupActionBarWithNavController import android.view.Menu import android.view.MenuItem import com.example.myapplication2.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

private lateinit var appBarConfiguration: AppBarConfiguration //创建 2 个变量
private lateinit var binding: ActivityMainBinding

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    binding = ActivityMainBinding.inflate(layoutInflater)
    setContentView(binding.root)

    setSupportActionBar(binding.toolbar)

    val navController = findNavController(R.id.nav_host_fragment_content_main)
    appBarConfiguration = AppBarConfiguration(navController.graph)
    setupActionBarWithNavController(navController, appBarConfiguration)

    binding.fab.setOnClickListener { view ->
        Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
            .setAction("Action", null).show()
    }
}

override fun onCreateOptionsMenu(menu: Menu): Boolean {
    // Inflate the menu; this adds items to the action bar if it is present.
    menuInflater.inflate(R.menu.menu_main, menu)
    return true
}

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    return when (item.itemId) {
        R.id.action_settings -> true
        else -> super.onOptionsItemSelected(item)
    }
}

override fun onSupportNavigateUp(): Boolean {
    val navController = findNavController(R.id.nav_host_fragment_content_main)
    return navController.navigateUp(appBarConfiguration)
            || super.onSupportNavigateUp()
}

}

我是个萌新,刚学 Kotlin,有没有推荐群一起学习?

按照以上代码,如果我有个按钮 id="create_button" ,按下载入 test_window.xml 窗口. test_window.xml 里面有什么讲究吗?