Add folder selection

lib/main.dart

@@ -1,4 +1,6 @@
+import 'package:file_picker/file_picker.dart';
 import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 import 'package:sheetless/sheetview.dart';
 
 import 'sheet.dart';
@@ -31,6 +33,40 @@ class MyHomePage extends StatefulWidget {
 }
 
 class _MyHomePageState extends State<MyHomePage> {
+  Future<String?> getSavedSheetsPath() async {
+    final prefs = await SharedPreferences.getInstance();
+    return prefs.getString("sheets-path");
+  }
+
+  Future<void> saveSheetsPath(String path) async {
+    final prefs = await SharedPreferences.getInstance();
+    prefs.setString("sheets-path", path);
+  }
+
+  Future<String?> askForSheetsPath() async {
+    return await FilePicker.platform.getDirectoryPath();
+  }
+
+  Future<String> findAndSaveSheetsPath() async {
+    String? savedSheetsPath = await getSavedSheetsPath();
+    if (savedSheetsPath != null) {
+      return savedSheetsPath;
+    }
+
+    String? selectedSheetsPath = await askForSheetsPath();
+    if (selectedSheetsPath != null) {
+      await saveSheetsPath(selectedSheetsPath);
+      return selectedSheetsPath;
+    }
+
+    return "No path selected";
+  }
+
+  Future<List<Sheet>> acquireSheets() async {
+    var sheetsPath = await findAndSaveSheetsPath();
+    return loadSheetsSorted(sheetsPath);
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -38,7 +74,7 @@ class _MyHomePageState extends State<MyHomePage> {
         title: const Text("My Sheets"),
       ),
       body: FutureBuilder(
-          future: loadSheetsSorted(),
+          future: acquireSheets(),
           builder: (BuildContext context, AsyncSnapshot<List<Sheet>> snapshot) {
             if (snapshot.hasData) {
               return SheetsWidget(

lib/sheet.dart

@@ -11,17 +11,16 @@ class Sheet {
   Sheet(this.author, this.name, this.path);
 }
 
-Future<List<Sheet>> loadSheetsSorted() async {
-  var sheets = await _loadSheets();
+Future<List<Sheet>> loadSheetsSorted(String path) async {
+  var sheets = await _loadSheets(path);
   sheets.sort((left, right) => left.name.compareTo(right.name));
   return sheets;
 }
 
-Future<List<Sheet>> _loadSheets() async {
-  // TODO: Handle directory not found
-  var dir = Directory("/home/julian/Nextcloud/jhome/Klavier-Noten/");
+Future<List<Sheet>> _loadSheets(String path) async {
+  var dir = Directory(path);
   if (!dir.existsSync()) {
-    throw Exception("Folder does not exist");
+    throw Exception("Specified path '$path' does not exist");
   }
   final List<Sheet> sheets = List.empty(growable: true);
   await for (final FileSystemEntity x in dir.list()) {