How to notify activity when a fragment's edit text has been edited (Android)?

I have an edittext in one of my fragments.
I also have a String field in my activity that starts the fragment, and every time the text changes in the edittext, I want to change the string in my activity accordingly but I'm not sure how to do that.

1. Create an interface like this

   interface OnDataChangeListener {
        fun onChange(string: String)
   }
   

2. In your fragment's constructor pass an instance of this interface as a parameter

   class MyFragment(val onDataChangeListener: OnDataChangeListener): Fragment
   

3. Now when the text changes in the edit text, call this interface's method

   editText.addTextChangedListener(object : TextWatcher{
        override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
        }
   
        override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
        }
   
        override fun afterTextChanged(s: Editable?) {
            onDataChangeListener.onChange(s.toString())
        }
    })
   

4. Now implement this interface in our activity

   class MainActivity : AppCompatActivity(), OnDataChangeListener {
   
     override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          setContentView(R.layout.activity_main)
   
          AppUtils.addFragment(this, MyFragment(this), R.id.fragment_container)
     }
   
     override fun onChange(string: String) {
          val textView = findViewById<TextView>(R.id.textView)
          textView.text = string
     }
   }
   

That's it. This should give you the required output.

Create an interface that the Activity implements and pass it to your Fragment. Then, add a TextWatcher to the EditText with editText.addTextWatcher() inside your Fragment, and notify the listener inside onTextChanged. This approach is based off the Android Docs.