see streetcomplete#213 (comment)

app/src/main/java/de/westnordost/streetcomplete/quests/address/AddAddressStreetForm.kt

@@ -1,7 +1,10 @@
 package de.westnordost.streetcomplete.quests.address
 
 import android.os.Bundle
+import android.view.LayoutInflater
 import android.view.View
+import android.view.ViewGroup
+import android.widget.EditText
 import androidx.appcompat.app.AlertDialog
 import de.westnordost.streetcomplete.R
 import de.westnordost.streetcomplete.quests.AbstractQuestFormAnswerFragment
@@ -16,7 +19,43 @@ class AddAddressStreetForm : AbstractQuestFormAnswerFragment<AddressStreetAnswer
             OtherAnswer(R.string.quest_address_street_no_named_streets) { confirmNoName() }
     )
 
-    private val placeName get() = nameInput?.text?.toString().orEmpty().trim()
+    private var streetNameInput: EditText? = null
+    private var placeNameInput: EditText? = null
+
+    private val locationName get() = nameInput?.text?.toString().orEmpty().trim()
+
+    private var isPlaceName: Boolean = false
+
+    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
+        val view = super.onCreateView(inflater, container, savedInstanceState)
+
+        isPlaceName = savedInstanceState?.getBoolean(AddAddressStreetForm.IS_PLACE_NAME) ?: false
+        setLayout(if(isPlaceName) R.layout.quest_housename else R.layout.quest_housenumber)
+
+        return view
+    }
+
+    private fun setLayout(layoutResourceId: Int) {
+        val view = setContentView(layoutResourceId)
+
+        streetNameInput = view.findViewById(R.id.houseNumberInput)
+        placeNameInput = view.findViewById(R.id.houseNameInput)
+
+        val onChanged = TextChangedWatcher { checkIsFormComplete() }
+        houseNumberInput?.addTextChangedListener(onChanged)
+        houseNameInput?.addTextChangedListener(onChanged)
+
+        // streetNumber is always optional
+        val input = AddHousenumberForm.getFirstNonNull(blockNumberInput, houseNumberInput, houseNameInput, conscriptionNumberInput)
+        input?.requestFocus()
+
+        initKeyboardButton(view)
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        outState.putBoolean(AddHousenumberForm.IS_HOUSENAME, isHousename)
+    }
 
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
@@ -25,16 +64,24 @@ class AddAddressStreetForm : AbstractQuestFormAnswerFragment<AddressStreetAnswer
     }
 
     override fun onClickOk() {
-        applyAnswer(StreetName(placeName))
+        applyAnswer(StreetName(locationName))
     }
 
     private fun confirmNoName() {
         AlertDialog.Builder(activity!!)
                 .setTitle(R.string.quest_name_answer_noName_confirmation_title)
-                .setPositiveButton(R.string.quest_name_noName_confirmation_positive) { _, _ -> applyAnswer(PlaceName("TODO")) } //TODO!
+                .setPositiveButton(R.string.quest_name_noName_confirmation_positive) { _, _ -> switchToPlaceName() } //TODO!
                 .setNegativeButton(R.string.quest_generic_confirmation_no, null)
                 .show()
     }
 
-    override fun isFormComplete() = placeName.isNotEmpty()
+    fun switchToPlaceName() {
+        isPlaceName = true
+    }
+
+    override fun isFormComplete() = locationName.isNotEmpty()
+
+    companion object {
+        private const val IS_PLACE_NAME = "is_place_name"
+    }
 }