calculate amount on quantity input

StockBuyActivity.kt

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

        val symbol = intent.getStringExtra(SYMBOL_KEY) ?: throw IllegalArgumentException()
        isSellForm = intent.getBooleanExtra(SELL_KEY, false)
        buyStockButton.setText(if (isSellForm) R.string.action_sell_stock else R.string.action_buy_stock)
        categoryStockViewModel.tags = symbol
        radioButtonByText = indexRadioButtonChildren()
        fetchContent()

        amountRadioGroup.setOnCheckedChangeListener { group: RadioGroup?, checkedId: Int ->
            onCheckedChange(group, checkedId)
        }
        amountEditText.addTextChangedListener {
            amountChanged(it.toString())
        }
        buyStockButton.setBlockingOnClickListener {
            buyStockClick()
        }

        viewModel.preOrderStockTransaction.observe(this, Observer { resource ->
            preOrderStockResource(resource)
        })
        amountEditText.addTextChangedListener {
            amountErrorTextView.text = ""
            val amount = it.toString().toDoubleOrNull()

            if (amount != null) {
                quantityEditText.setText(String.format("%.4f", (amount / askPrice)))
            } else {
                quantityEditText.setText("")
            }
        }
        quantityEditText.addTextChangedListener {
            quantityErrorTextView.text = ""
            //Hangs for some reason
            val quantity = it.toString().toDoubleOrNull()
            if (quantity != null) {
                println((quantity * askPrice))
                amountEditText.setText(String.format("%.4f", (quantity * askPrice)))
            } else {
                amountEditText.setText("")
            }
        }
        priceEditText.addTextChangedListener {
            priceErrorTextView.text = ""
        }
        orderTypeRadioGroup.setOnCheckedChangeListener { _: RadioGroup?, checkedId: Int ->
            orderTypeChanged(checkedId)
        }
        orderTypeChanged(R.id.marketOrderRadioButton)
    }

Line 41 and 43 are the reason it hangs. You are setting the text of the editText inside a textChangeListener of the editText so there will be infinite loop as the new text you set will also call the listener which will call setText again and so on.

Suggested fix:

1. create a variable to hold the textChangedListener of :
   I. AmountEditeText
   ii. QuantityEditText
   I. e

val amountListener = ...
val quantityListenr = ... {
}
amountEditText.addTextChangedListener {
            amountErrorTextView.text = ""
            val amount = it.toString().toDoubleOrNull()
            quantityEditText.removeTextChangeListener(quantityListener)
            if (amount != null) {
                quantityEditText.setText(String.format("%.4f", (amount / askPrice)))
            } else {
                quantityEditText.setText("")
            }
           quantityEditText.addTextChangeListener(quantityListener)
        }
        quantityEditText.addTextChangedListener {
            quantityErrorTextView.text = ""
            //Hangs for some reason
            val quantity = it.toString().toDoubleOrNull()
                quantityEditText.removeTextChangeListener(amountListener)
            if (quantity != null) {
                println((quantity * askPrice))
                amountEditText.setText(String.format("%.4f", (quantity * askPrice)))
            } else {
                amountEditText.setText("")
            }
                amountEditText.addTextChangeListener(amountListener)
        } 

val amountListener = object : TextWatcher{
            override fun afterTextChanged(p0: Editable?) {
               amountErrorTextView.text = ""
            val amount = it.toString().toDoubleOrNull()

            if (amount != null) {
                quantityEditText.setText(String.format("%.4f", (amount / askPrice)))
            } else {
                quantityEditText.setText("")
            }
            }

            override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}

            override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}
        }

val quantityListener = object : TextWatcher{
            override fun afterTextChanged(p0: Editable?) {
                quantityErrorTextView.text = ""
            //Hangs for some reason
            val quantity = it.toString().toDoubleOrNull()
            if (quantity != null) {
                println((quantity * askPrice))
                amountEditText.setText(String.format("%.4f", (quantity * askPrice)))
            } else {
                amountEditText.setText("")
            }
            }

            override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}

            override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}
        }

so this:

amountEditText.addTextChangedListener {
            amountErrorTextView.text = ""
            val amount = it.toString().toDoubleOrNull()

            if (amount != null) {
                quantityEditText.setText(String.format("%.4f", (amount / askPrice)))
            } else {
                quantityEditText.setText("")
            }
        }

changes to
amountEditText.addTextChangedListener(amountListener)
and so on.

heres what i got currently:

 val amountListener = object : TextWatcher{
        override fun afterTextChanged(p0: Editable?) {
            amountErrorTextView.text = ""
            val amount = p0.toString().toDoubleOrNull()
            // Obviuosly enters a recursive problem
//           quantityEditText.removeTextChangedListener(quantityListener)
            if (amount != null) {
                quantityEditText.setText(String.format("%.4f", (amount / askPrice)))
            } else {
                quantityEditText.setText("")
            }
        }

        override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}

        override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}
    }

    val quantityListener = object :  TextWatcher {
        override fun afterTextChanged(p0: Editable?) {
            quantityErrorTextView.text = ""

            val quantity = p0.toString().toDoubleOrNull()
            //remove listener
            amountEditText.removeTextChangedListener(amountListener)
            if (quantity != null) {
                println((quantity * askPrice))
                amountEditText.setText(String.format("%.4f", (quantity * askPrice)))
            } else {
                amountEditText.setText("")
            }
            //add listener
            amountEditText.addTextChangedListener(amountListener)
        }

        override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}

        override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}
    }




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

        val symbol = intent.getStringExtra(SYMBOL_KEY) ?: throw IllegalArgumentException()
        isSellForm = intent.getBooleanExtra(SELL_KEY, false)
        buyStockButton.setText(if (isSellForm) R.string.action_sell_stock else R.string.action_buy_stock)
        categoryStockViewModel.tags = symbol
        radioButtonByText = indexRadioButtonChildren()
        fetchContent()

        amountRadioGroup.setOnCheckedChangeListener { group: RadioGroup?, checkedId: Int ->
            onCheckedChange(group, checkedId)
        }
        amountEditText.addTextChangedListener {
            amountChanged(it.toString())
        }
        buyStockButton.setBlockingOnClickListener {
            buyStockClick()
        }

        viewModel.preOrderStockTransaction.observe(this, Observer { resource ->
            preOrderStockResource(resource)
        })


        amountEditText.addTextChangedListener(amountListener)
        quantityEditText.addTextChangedListener(quantityListener)

Remove this line:

amountEditText.addTextChangedListener {
amountChanged(it.toString())
}