link editor: preset link from attributes (#597)

lib/src/widgets/toolbar/link_dialog.dart

@@ -4,16 +4,26 @@ import '../../models/themes/quill_dialog_theme.dart';
 import '../../translations/toolbar.i18n.dart';
 
 class LinkDialog extends StatefulWidget {
-  const LinkDialog({this.dialogTheme, Key? key}) : super(key: key);
+  const LinkDialog({this.dialogTheme, this.link, Key? key})
+      : super(key: key);
 
   final QuillDialogTheme? dialogTheme;
+  final String? link;
 
   @override
   LinkDialogState createState() => LinkDialogState();
 }
 
 class LinkDialogState extends State<LinkDialog> {
-  String _link = '';
+  late String _link;
+  late TextEditingController _controller;
+
+  @override
+  void initState() {
+    super.initState();
+    _link = widget.link ?? '';
+    _controller = TextEditingController(text: _link);
+  }
 
   @override
   Widget build(BuildContext context) {
@@ -27,6 +37,7 @@ class LinkDialogState extends State<LinkDialog> {
             floatingLabelStyle: widget.dialogTheme?.labelTextStyle),
         autofocus: true,
         onChanged: _linkChanged,
+        controller: _controller,
       ),
       actions: [
         TextButton(

lib/src/widgets/toolbar/link_style_button.dart

@@ -99,7 +99,10 @@ class _LinkStyleButtonState extends State<LinkStyleButton> {
     showDialog<String>(
       context: context,
       builder: (ctx) {
-        return LinkDialog(dialogTheme: widget.dialogTheme);
+        final link = widget.controller
+            .getSelectionStyle()
+            .attributes[Attribute.link.key]?.value;
+        return LinkDialog(dialogTheme: widget.dialogTheme, link: link);
       },
     ).then(_linkSubmitted);
   }