我有一个子活动，我按下两个按钮，一个递增，一个递减。我想在返回前一个活动时保存这个数字。但是，我被困在这里。我尝试使用共享首选项，然而，这似乎适用于主要到次要的活动。我试着使用活动结果，这似乎远远超出了我现在。我希望textView中的值保持不变，直到我按下一个按钮重置整个过程。
这是父活动。

import android.app.Activity
import android.content.Intent
import android.os.Bundle
import android.widget.Button
import androidx.activity.result.contract.ActivityResultContracts
import androidx.appcompat.app.AppCompatActivity

class TallBoys : AppCompatActivity() {

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

    val btn1: Button = findViewById(R.id.button1)
    val btn2: Button = findViewById(R.id.button2)
    val btn3: Button = findViewById(R.id.button3)
    val btn4: Button = findViewById(R.id.button4)
    val btn5: Button = findViewById(R.id.button5)
    val btn6: Button = findViewById(R.id.button6)
    val btn7: Button = findViewById(R.id.button7)


    btn1.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)

    }

    btn2.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)
        startActivity(intent)
    }

    btn3.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)
        startActivity(intent)
    }
    btn4.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)
        startActivity(intent)
    }
    btn5.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)
        startActivity(intent)
    }
    btn6.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)
        startActivity(intent)
    }
    btn7.setOnClickListener {
        val intent = Intent(this, TallBoysNumbers::class.java)
        startActivity(intent)
    }

}

}
这是子活动

import android.app.Activity
import android.content.Intent
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class TallBoysNumbers : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_tall_boys_numbers)



    val confirmBtn: Button = findViewById(R.id.confirm_button)
    val plusBtn: Button = findViewById(R.id.plus)
    val textView = findViewById<TextView>(R.id.numbers)
    val negBtn: Button = findViewById(R.id.negative)
    var count = 0


    plusBtn.setOnClickListener {
        count++
        textView.text = count.toString()
        if (count >= 8) {
            plusBtn.isEnabled = false
            negBtn.isEnabled = true
        }

    }

    negBtn.setOnClickListener {
        count--
        textView.text = count.toString()
        if (count <= 0) {
            negBtn.isEnabled = false
            plusBtn.isEnabled = true
        }
    }



        confirmBtn.setOnClickListener {
            finish()
        }
    }
}