Implemented "cancel download" button.

Requires PR #165 to be merged in quickemu.

lib/src/pages/downloader.dart

@@ -33,6 +33,7 @@ class _DownloaderState extends State<Downloader> {
   late final Stream<double> _progressStream;
   bool _downloadFinished = false;
   var controller = StreamController<double>();
+  Process? _process;
 
   @override
   void initState() {
@@ -83,6 +84,10 @@ class _DownloaderState extends State<Downloader> {
           _downloadFinished = true;
         });
       });
+
+      setState(() {
+        _process = process;
+      });
     });
     return controller.stream;
   }
@@ -125,6 +130,9 @@ class _DownloaderState extends State<Downloader> {
             ),
           ),
           CancelDismissButton(
+            onCancel: () {
+              _process?.kill();
+            },
             downloadFinished: _downloadFinished,
           ),
         ],

lib/src/widgets/downloader/cancel_dismiss_button.dart

@@ -4,9 +4,11 @@ class CancelDismissButton extends StatelessWidget {
   const CancelDismissButton({
     Key? key,
     required this.downloadFinished,
+    required this.onCancel,
   }) : super(key: key);
 
   final bool downloadFinished;
+  final VoidCallback onCancel;
 
   @override
   Widget build(BuildContext context) {
@@ -17,7 +19,7 @@ class CancelDismissButton extends StatelessWidget {
         children: [
           ElevatedButton(
             onPressed: !downloadFinished
-                ? null
+                ? onCancel
                 : () {
                     Navigator.of(context).pop();
                   },