feat: removing the QR code on visibility hint no longer visible

app/src/main/java/org/thoughtcrime/securesms/loki/fragments/ScanQRCodeWrapperFragment.kt

@@ -3,18 +3,36 @@ package org.thoughtcrime.securesms.loki.fragments
 import android.Manifest
 import android.content.pm.PackageManager
 import android.os.Bundle
-import androidx.fragment.app.Fragment
-import androidx.core.content.ContextCompat
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import androidx.core.content.ContextCompat
+import androidx.fragment.app.Fragment
 import com.tbruyelle.rxpermissions2.RxPermissions
 import network.loki.messenger.R
 import org.thoughtcrime.securesms.qr.ScanListener
 
 class ScanQRCodeWrapperFragment : Fragment(), ScanQRCodePlaceholderFragmentDelegate, ScanListener {
+
+    companion object {
+        const val FRAGMENT_TAG = "ScanQRCodeWrapperFragment_FRAGMENT_TAG"
+    }
+
     var delegate: ScanQRCodeWrapperFragmentDelegate? = null
     var message: CharSequence = ""
+    var enabled: Boolean = true
+    set(value) {
+        val shouldUpdate = field != value // update if value changes (view appears or disappears)
+        field = value
+        if (shouldUpdate) {
+            update()
+        }
+    }
+
+    override fun setUserVisibleHint(isVisibleToUser: Boolean) {
+        super.setUserVisibleHint(isVisibleToUser)
+         enabled = isVisibleToUser
+    }
 
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
         return inflater.inflate(R.layout.fragment_scan_qr_code_wrapper, container, false)
@@ -26,7 +44,17 @@ class ScanQRCodeWrapperFragment : Fragment(), ScanQRCodePlaceholderFragmentDeleg
     }
 
     private fun update() {
+        if (!this.isAdded) return
+
         val fragment: Fragment
+        if (!enabled) {
+            val manager = childFragmentManager
+            manager.findFragmentByTag(FRAGMENT_TAG)?.let { existingFragment ->
+                // remove existing camera fragment (if switching back to other page)
+                manager.beginTransaction().remove(existingFragment).commit()
+            }
+            return
+        }
         if (ContextCompat.checkSelfPermission(requireActivity(), Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) {
             val scanQRCodeFragment = ScanQRCodeFragment()
             scanQRCodeFragment.scanListener = this
@@ -38,7 +66,7 @@ class ScanQRCodeWrapperFragment : Fragment(), ScanQRCodePlaceholderFragmentDeleg
             fragment = scanQRCodePlaceholderFragment
         }
         val transaction = childFragmentManager.beginTransaction()
-        transaction.replace(R.id.fragmentContainer, fragment)
+        transaction.replace(R.id.fragmentContainer, fragment, FRAGMENT_TAG)
         transaction.commit()
     }
 
@@ -59,6 +87,5 @@ class ScanQRCodeWrapperFragment : Fragment(), ScanQRCodePlaceholderFragmentDeleg
 }
 
 interface ScanQRCodeWrapperFragmentDelegate {
-
     fun handleQRCodeScanned(string: String)
 }