Basic savedInstanceState bundle usage.

Restores hidden pages, zoom level, approximate scroll, autocrop, after Activity is soft-reset by things like Splitscreen toggling.

app/src/main/java/com/lhw/pdf/MainActivity.kt

@@ -41,10 +41,7 @@ class MainActivity : AppCompatActivity() {
     private val thumbnailHeight = 700
     private var renderAutoCrop = true
     private var pagesPerLandscape = 3F
-        private set(pages) {
+    private var thumbnailScrollProgress = 0F
-            field = pages
-            updatePresentations()
-        }
     private var usePdfBox = false
     private val presentations = mutableMapOf<Int, MyPresentation>()
     private lateinit var pdfDocument: PdfDocument
@@ -52,6 +49,11 @@ class MainActivity : AppCompatActivity() {
     private val thumbnailImageViews = mutableListOf<ImageView>()
     private val defaultCachedFileName = "cached.pdf"
 
+    private fun setPagesPerLandscape(pages: Float) {
+        pagesPerLandscape = pages
+        updatePresentations()
+    }
+
     private val displayListener = object: DisplayListener {
         override fun onDisplayAdded(p0: Int) {
             reevaluateDisplay(p0)
@@ -93,7 +95,7 @@ class MainActivity : AppCompatActivity() {
 
     private fun updatePresentationImages(p: MyPresentation) {
         val maxHeight: Int = p.displayMetrics.heightPixels
-        val maxWidth: Int = min(maxHeight * 5 / 7, (p.displayMetrics.widthPixels / pagesPerLandscape).toInt())
+        val maxWidth: Int = (p.displayMetrics.widthPixels / pagesPerLandscape).toInt()  //in(maxHeight * 5 / 7, (p.displayMetrics.widthPixels / pagesPerLandscape).toInt())
         updateBitmaps(maxWidth, maxHeight)
         val key = Pair(maxWidth, maxHeight)
         val bitmaps = showPages.withIndex()
@@ -128,6 +130,7 @@ class MainActivity : AppCompatActivity() {
     }
 
     private fun populateThumbnails() {
+        showPages.clear()
         for ((index, bitmap) in pdfDocument.bitmapThumbnails) {
             val img = ImageView(this)
             img.setImageBitmap(bitmap)
@@ -159,6 +162,16 @@ class MainActivity : AppCompatActivity() {
         displayText.text = text.toString()
     }
 
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        // Store some things to restore
+        outState.putString("fileName", "TODO")
+        outState.putBoolean("renderAutoCrop", renderAutoCrop)
+        outState.putFloat("pagesPerLandscape", pagesPerLandscape)
+        outState.putBooleanArray("showPages", showPages.toBooleanArray())
+        outState.putFloat("thumbnailScrollProgress", thumbnailScrollProgress)
+    }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         //enableEdgeToEdge()
         super.onCreate(savedInstanceState)
@@ -177,6 +190,7 @@ class MainActivity : AppCompatActivity() {
         setSupportActionBar(binding.appBarMain.toolbar)
 
         // Load previous pdf, or included test pdf first
+        val lastFileName = savedInstanceState?.getString("fileName")  // TODO: proper filenames
         var file = File(cacheDir, defaultCachedFileName)
         if (!file.exists()) {
             file = inputStreamToCache(defaultCachedFileName, resources.openRawResource(R.raw.testpdf))
@@ -185,17 +199,26 @@ class MainActivity : AppCompatActivity() {
         // Then overwrite it with any pdf sent via intent
         handleIntent(intent)
 
+        renderAutoCrop = savedInstanceState?.getBoolean("renderAutoCrop") ?: true
+
         pdfDocument.renderThumbnails(thumbnailWidth, thumbnailHeight)
         displayManager.getDisplays(DisplayManager.DISPLAY_CATEGORY_PRESENTATION).forEach(::makePresentationView)
-        populateThumbnails()
+        populateThumbnails()  // Populates showPages
+        savedInstanceState?.getBooleanArray("showPages")?.forEachIndexed { i, show ->
+            showPages[i] = show
+        }
+        reLayoutThumbnails()
 
         val container = binding.appBarMain.contentMain.thumbnailsLayout
         val containerScroll = binding.appBarMain.contentMain.thumbnailsScroll
         containerScroll.viewTreeObserver.addOnScrollChangedListener {
-            val progress = containerScroll.scrollX.toFloat() / (container.width - containerScroll.width)
+            thumbnailScrollProgress = containerScroll.scrollX.toFloat() / (container.width - containerScroll.width)
-            presentations.values.forEach {it.setScrollProgress(progress)}
+            presentations.values.forEach {it.setScrollProgress(thumbnailScrollProgress)}
         }
+        savedInstanceState?.getFloat("thumbnailScrollProgress")?.let { thumbnailScrollProgress = it }
+        containerScroll.scrollTo((thumbnailScrollProgress * (container.width - containerScroll.width)).toInt(), 0)
 
+        savedInstanceState?.getFloat("pagesPerLandscape")?.let { pagesPerLandscape = it }
         val pageZoomLevels = arrayOf(1F, 1.5F, 2F, 2.5F, 3F, 3.5F, 4F, 5F, 6F, 8F, 10F)
         val chipGroupPages = binding.appBarMain.contentMain.chipGroupPages
         pageZoomLevels.forEach { pages ->
@@ -203,7 +226,7 @@ class MainActivity : AppCompatActivity() {
             chip.text = "$pages pages"
             chip.isCheckable = true
             chip.isChecked = (pages == pagesPerLandscape)
-            chip.setOnCheckedChangeListener { _, checked -> if (checked) pagesPerLandscape = pages }
+            chip.setOnCheckedChangeListener { _, checked -> if (checked) setPagesPerLandscape(pages) }
             chipGroupPages.addView(chip)
         }
         binding.appBarMain.contentMain.chipAutoCrop.setOnCheckedChangeListener { _, checked ->