added map cache

lib/widgets/base_layer_widget.dart

@@ -1,22 +1,24 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_map/flutter_map.dart';
+import 'package:flutter_map_tile_caching/flutter_map_tile_caching.dart';
 
 class BaseLayer extends StatelessWidget {
   const BaseLayer({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
-    return TileLayerWidget(
-      options: TileLayerOptions(
-        backgroundColor: Colors.transparent,
-        //urlTemplate: 'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png',
-        urlTemplate: 'https://cyberjapandata.gsi.go.jp/xyz/std/{z}/{x}/{y}.png',
-        //urlTemplate: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}',
-        //subdomains: ['a', 'b', 'c'],
-        //subdomains: ['TileMatrix', 'TileCol', 'TileRow'],
-
-      ),
-    );
+    return TileLayer(
+                    urlTemplate: "https://cyberjapandata.gsi.go.jp/xyz/std/{z}/{x}/{y}.png",
+                    tileProvider: FMTC.instance('OpenStreetMap (A)').getTileProvider(
+                              FMTCTileProviderSettings(
+                                behavior: CacheBehavior.values
+                                    .byName('cacheFirst'),
+                                cachedValidDuration: Duration(
+                                        days: 14
+                                      ),
+                              ),
+                            ),
+                  );
   }
 }