feat: Taking Snapshots of the map

It is now possible to take snapshots of the displayed map.

Fixes #25

Author: luis

example/lib/main.dart

@@ -16,6 +16,7 @@ import 'package:apple_maps_flutter_example/place_circle.dart';
 import 'package:apple_maps_flutter_example/place_polygon.dart';
 import 'package:apple_maps_flutter_example/place_polyline.dart';
 import 'package:apple_maps_flutter_example/scrolling_map.dart';
+import 'package:apple_maps_flutter_example/snapshot.dart';
 import 'package:flutter/material.dart';
 
 final List<ExamplePage> _allPages = <ExamplePage>[
@@ -32,6 +33,7 @@ final List<ExamplePage> _allPages = <ExamplePage>[
   PlaceCirclePage(),
   ScrollingMapPage(),
   MapUpdatePage(),
+  SnapshotPage(),
 ];
 
 class MapsDemo extends StatelessWidget {

example/lib/snapshot.dart

@@ -0,0 +1,71 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// ignore_for_file: public_member_api_docs
+
+import 'dart:typed_data';
+
+import 'package:apple_maps_flutter_example/page.dart';
+import 'package:flutter/material.dart';
+import 'package:apple_maps_flutter/apple_maps_flutter.dart';
+
+const CameraPosition _kInitialPosition =
+    CameraPosition(target: LatLng(-33.852, 151.211), zoom: 11.0);
+
+class SnapshotPage extends ExamplePage {
+  SnapshotPage()
+      : super(const Icon(Icons.camera_alt), 'Take a snapshot of the map');
+
+  @override
+  Widget build(BuildContext context) {
+    return _SnapshotBody();
+  }
+}
+
+class _SnapshotBody extends StatefulWidget {
+  @override
+  _SnapshotBodyState createState() => _SnapshotBodyState();
+}
+
+class _SnapshotBodyState extends State<_SnapshotBody> {
+  AppleMapController? _mapController;
+  Uint8List? _imageBytes;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.all(16),
+      child: Column(
+        crossAxisAlignment: CrossAxisAlignment.stretch,
+        children: [
+          SizedBox(
+            height: 180,
+            child: AppleMap(
+              onMapCreated: onMapCreated,
+              initialCameraPosition: _kInitialPosition,
+            ),
+          ),
+          TextButton(
+            child: Text('Take a snapshot'),
+            onPressed: () async {
+              final imageBytes = await _mapController?.takeSnapshot();
+              setState(() {
+                _imageBytes = imageBytes;
+              });
+            },
+          ),
+          Container(
+            decoration: BoxDecoration(color: Colors.blueGrey[50]),
+            height: 180,
+            child: _imageBytes != null ? Image.memory(_imageBytes!) : null,
+          ),
+        ],
+      ),
+    );
+  }
+
+  void onMapCreated(AppleMapController controller) {
+    _mapController = controller;
+  }
+}

ios/Classes/MapView/AppleMapController.swift

@@ -16,6 +16,8 @@ public class AppleMapController: NSObject, FlutterPlatformView {
     var options: [String: Any]
     var onCalloutTapGestureRecognizer: UITapGestureRecognizer?
     var currentlySelectedAnnotation: String?
+    var snapShotOptions: MKMapSnapshotter.Options = MKMapSnapshotter.Options()
+    var snapShot: MKMapSnapshotter?
 
     let availableCaps: Dictionary<String, CGLineCap> = [
         "buttCap": CGLineCap.butt,
@@ -78,7 +80,7 @@ public class AppleMapController: NSObject, FlutterPlatformView {
     }
 
     private func setMethodCallHandlers() {
-        channel.setMethodCallHandler({ [unowned self] (call: FlutterMethodCall, result: FlutterResult) -> Void in
+        channel.setMethodCallHandler({ [unowned self] (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
             if let args :Dictionary<String, Any> = call.arguments as? Dictionary<String,Any> {
                 switch(call.method) {
                 case "annotations#update":
@@ -151,6 +153,10 @@ public class AppleMapController: NSObject, FlutterPlatformView {
                 case "map#isMyLocationButtonEnabled":
                     result(self.mapView.isMyLocationButtonShowing ?? false)
                     break
+                case "map#takeSnapshot":
+                    self.takeSnapshot(onCompletion: { (snapshot: FlutterStandardTypedData?, error: Error?) -> Void in
+                        result(snapshot ?? error)
+                    })
                 case "map#getMinMaxZoomLevels":
                     result([self.mapView.minZoomLevel, self.mapView.maxZoomLevel])
                     break
@@ -341,3 +347,25 @@ extension AppleMapController: MKMapViewDelegate {
         return MKOverlayRenderer()
     }
 }
+
+extension AppleMapController {
+    private func takeSnapshot(onCompletion: @escaping (FlutterStandardTypedData?, Error?) -> Void) {
+        // MKMapSnapShotOptions setting.
+        snapShotOptions.region = self.mapView.region
+        snapShotOptions.size = self.mapView.frame.size
+        snapShotOptions.scale = UIScreen.main.scale
+        
+        // Set MKMapSnapShotOptions to MKMapSnapShotter.
+        snapShot = MKMapSnapshotter(options: snapShotOptions)
+        
+        snapShot?.cancel()
+        
+        snapShot?.start(completionHandler: {(snapshot: MKMapSnapshotter.Snapshot?, error: Error?) -> Void in
+            if let imageData = snapshot?.image.pngData() {
+                onCompletion(FlutterStandardTypedData.init(bytes: imageData), nil)
+            } else {
+                onCompletion(nil, error)
+            }
+        })
+    }
+}

lib/src/controller.dart

@@ -233,4 +233,9 @@ class AppleMapController {
     final doubles = List<double>.from(point?['point']);
     return Offset(doubles.first, doubles.last);
   }
+
+  /// Returns the image bytes of the map
+  Future<Uint8List?> takeSnapshot() {
+    return channel.invokeMethod<Uint8List>('map#takeSnapshot');
+  }
 }