diff --git a/app/src/main/java/com/lhw/pdf/MainActivity.kt b/app/src/main/java/com/lhw/pdf/MainActivity.kt
index 335efdd..c0790ef 100644
--- a/app/src/main/java/com/lhw/pdf/MainActivity.kt
+++ b/app/src/main/java/com/lhw/pdf/MainActivity.kt
@@ -3,9 +3,13 @@ package com.lhw.pdf
 import android.content.Context
 import android.content.Intent
 import android.graphics.PorterDuff
+import android.hardware.display.DisplayManager
+import android.hardware.display.DisplayManager.DisplayListener
 import android.media.MediaRouter
 import android.os.Bundle
+import android.util.DisplayMetrics
 import android.view.Menu
+import android.view.WindowManager
 import android.widget.ImageView
 import com.google.android.material.snackbar.Snackbar
 import com.google.android.material.navigation.NavigationView
@@ -28,6 +32,7 @@ import kotlin.math.min
 class MainActivity : AppCompatActivity() {
     private lateinit var appBarConfiguration: AppBarConfiguration
     private lateinit var binding: ActivityMainBinding
+    private lateinit var displayManager: DisplayManager
     private lateinit var mediaRouter: MediaRouter
     private val thumbnailWidth = 500
     private val thumbnailHeight = 700
@@ -39,6 +44,20 @@ class MainActivity : AppCompatActivity() {
     private val thumbnailImageViews = mutableListOf<ImageView>()
     private val defaultCachedFileName = "cached.pdf"
 
+    private val displayListener = object: DisplayListener {
+        override fun onDisplayAdded(p0: Int) {
+            updateDisplayText()
+        }
+
+        override fun onDisplayChanged(p0: Int) {
+            updateDisplayText()
+        }
+
+        override fun onDisplayRemoved(p0: Int) {
+            updateDisplayText()
+        }
+    }
+
     private fun inputStreamToCache(outputFilename: String, inputStream: InputStream): File {
         val fileCached = File(cacheDir, outputFilename)
         val output = FileOutputStream(fileCached)
@@ -67,9 +86,11 @@ class MainActivity : AppCompatActivity() {
     }
 
     private fun makePresentationView() {
+        presentation = null
         mediaRouter.getSelectedRoute(MediaRouter.ROUTE_TYPE_LIVE_VIDEO)?.presentationDisplay?.let { display ->
             presentation = MyPresentation(this, display)
             updatePresentationImages()
+            presentation?.setOnCancelListener { presentation = null }
             presentation?.show()
         }
     }
@@ -101,8 +122,26 @@ class MainActivity : AppCompatActivity() {
         reLayoutThumbnails()
     }
 
+    private fun updateDisplayText() {
+        val displayText = binding.appBarMain.contentMain.textDisplays
+        val text = StringBuilder()
+        //displayManager.getDisplays(DisplayManager.DISPLAY_CATEGORY_PRESENTATION).forEach {
+        displayManager.displays.forEach {
+            val displayMetrics = DisplayMetrics()
+            @Suppress("DEPRECATION")
+            it.getMetrics(displayMetrics)
+            val s = "displayId ${it.displayId} $displayMetrics"
+            println(s)
+            text.append(s)
+            text.append("\n")
+        }
+        displayText.text = text.toString()
+    }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
+        displayManager = getSystemService(Context.DISPLAY_SERVICE) as DisplayManager
         mediaRouter = getSystemService(Context.MEDIA_ROUTER_SERVICE) as MediaRouter
         //val windowInsetsController = WindowCompat.getInsetsController(window, window.decorView)
         //windowInsetsController.hide(WindowInsetsCompat.Type.systemBars())  //Doesn't seem to actually fill the vacant space by default
@@ -110,6 +149,9 @@ class MainActivity : AppCompatActivity() {
         binding = ActivityMainBinding.inflate(layoutInflater)
         setContentView(binding.root)
 
+        updateDisplayText()
+        displayManager.registerDisplayListener(displayListener, null)
+
         setSupportActionBar(binding.appBarMain.toolbar)
 
         // Load previous pdf, or included test pdf first
diff --git a/app/src/main/res/layout/content_main.xml b/app/src/main/res/layout/content_main.xml
index c1892e8..8b41bc3 100644
--- a/app/src/main/res/layout/content_main.xml
+++ b/app/src/main/res/layout/content_main.xml
@@ -54,4 +54,18 @@
             android:orientation="horizontal"
             tools:showIn="@layout/content_main" />
     </HorizontalScrollView>
+
+    <TextView
+        android:id="@+id/text_displays"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginStart="8dp"
+        android:layout_marginTop="308dp"
+        android:layout_marginEnd="8dp"
+        android:textAlignment="center"
+        android:textSize="20sp"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
 </androidx.constraintlayout.widget.ConstraintLayout>
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