Use SAF for Android

lib/sheet.dart

@@ -11,27 +11,34 @@ class Sheet {
   Sheet(this.author, this.name, this.path);
 }
 
-Future<List<Sheet>> loadSheetsSorted(String path) async {
-  var sheets = await _loadSheets(path);
+Future<List<Sheet>> loadSheetsSorted(List<String> sheetsDirectoryFiles) async {
+  var sheets = await _loadSheets(sheetsDirectoryFiles);
   sheets.sort((left, right) => left.name.compareTo(right.name));
   return sheets;
 }
 
-Future<List<Sheet>> _loadSheets(String path) async {
-  var dir = Directory(path);
-  if (!dir.existsSync()) {
-    throw Exception("Specified path '$path' does not exist");
-  }
+Future<List<Sheet>> _loadSheets(List<String> sheetsDirectoryFiles) async {
   final List<Sheet> sheets = List.empty(growable: true);
-  await for (final FileSystemEntity x in dir.list()) {
-    if (x is Directory) {
-      var authorName = p.basename(x.path);
-      await for (final FileSystemEntity a in x.list()) {
-        if (a is File) {
-          var sheetName = p.basenameWithoutExtension(a.path);
-          sheetName = sheetName.capitalize();
-          sheets.add(Sheet(authorName, sheetName, a.path));
+  var authorDirectories = sheetsDirectoryFiles
+      .map((e) => Directory(e))
+      .where((element) => element.existsSync());
+
+  for (Directory authorDirectory in authorDirectories) {
+    var authorName = p.basename(authorDirectory.path);
+    // Ignore hidden directories
+    if (authorName.startsWith(".")) {
+      continue;
+    }
+
+    await for (final FileSystemEntity sheetFile in authorDirectory.list()) {
+      if (sheetFile is File) {
+        var sheetName = p.basenameWithoutExtension(sheetFile.path);
+        // Ignore hidden files
+        if (sheetName.startsWith(".")) {
+          continue;
         }
+        sheetName = sheetName.capitalize();
+        sheets.add(Sheet(authorName, sheetName, sheetFile.path));
       }
     }
   }