问未解析的引用:活动错误

EN

package com.taylorworld.tw01

import android.content.Context
import android.os.Bundle
import com.google.android.material.snackbar.Snackbar
import androidx.appcompat.app.AppCompatActivity;
import android.view.Menu
import android.view.MenuItem
import android.view.View

import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.content_main.*

class MainActivity() : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    //setSupportActionBar(findViewById(R.id.my_toolbar))

    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 {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    return when (item.itemId) {
        R.id.action_settings -> true
        else -> super.onOptionsItemSelected(item)
    }
   }

    var strength = editText2.text.toString()
    var dexterity = editText.text.toString()
    var intelligance = editText4.text.toString()
    var wisdom = editText3.text.toString()
    var constitution = editText6.text.toString()
    var charisma = editText5.text.toString()
    var chrname = editText7.text.toString()

    val sharedPref = activity?.getPreferences(Context.MODE_PRIVATE)

    public fun saveStr(view: View) {

        val sharedPref = activity?.setPreferences(Context.MODE_PRIVATE) ?: return with(sharedPref.edit()) {
            putInt(getString(STR), strength)
            commit()
        }
     }

    public fun saveDex(view: View) {

        val sharedPref = activity?.setPreferences(Context.MODE_PRIVATE) ?: return with(sharedPref.edit()) {
            putInt(getString(DEX), dexterity)
            commit()
        }
     }

     public fun readStr(view: View) {

    }
    }