Improve update message dialog

lib/utils/ui_utils.dart

@@ -93,6 +93,7 @@ Future<String> askUserString({
   @required String defaultValue,
   @required String hint,
   int maxLength = 200,
+  int minLength = 1,
 }) async {
   assert(context != null);
   assert(title != null);
@@ -105,35 +106,13 @@ Future<String> askUserString({
 
   final confirm = await showDialog<bool>(
       context: context,
-      builder: (c) => AlertDialog(
-            title: Text(title),
-            content: AutoSizeDialogContentWidget(
-              child: Column(
-                children: <Widget>[
-                  Text(message),
-                  TextField(
-                    controller: controller,
-                    maxLines: null,
-                    maxLength: maxLength,
-                    keyboardType: TextInputType.text,
-                    decoration: InputDecoration(
-                      labelText: hint,
-                      alignLabelWithHint: true,
-                    ),
-                  )
-                ],
-              ),
-            ),
-            actions: <Widget>[
-              FlatButton(
-                child: Text(tr("Cancel").toUpperCase()),
-                onPressed: () => Navigator.pop(c, false),
-              ),
-              FlatButton(
-                child: Text(tr("OK")),
-                onPressed: () => Navigator.pop(c, true),
-              ),
-            ],
+      builder: (c) => _InputTextDialog(
+            title: title,
+            message: message,
+            controller: controller,
+            maxLength: maxLength,
+            minLength: minLength,
+            hint: hint,
           ));
 
   if (confirm == null || !confirm) return null;
@@ -141,6 +120,65 @@ Future<String> askUserString({
   return controller.text;
 }
 
+class _InputTextDialog extends StatefulWidget {
+  final String title;
+  final String message;
+  final TextEditingController controller;
+  final int maxLength;
+  final int minLength;
+  final String hint;
+
+  const _InputTextDialog({
+    Key key,
+    @required this.title,
+    @required this.message,
+    @required this.controller,
+    @required this.maxLength,
+    @required this.minLength,
+    @required this.hint,
+  }) : super(key: key);
+
+  @override
+  __InputTextDialogState createState() => __InputTextDialogState();
+}
+
+class __InputTextDialogState extends State<_InputTextDialog> {
+  @override
+  Widget build(BuildContext c) => AlertDialog(
+        title: Text(widget.title),
+        content: AutoSizeDialogContentWidget(
+          child: Column(
+            children: <Widget>[
+              Text(widget.message),
+              TextField(
+                controller: widget.controller,
+                maxLines: null,
+                maxLength: widget.maxLength,
+                keyboardType: TextInputType.text,
+                onChanged: (s) => setState(() {}),
+                decoration: InputDecoration(
+                  labelText: widget.hint,
+                  alignLabelWithHint: true,
+                ),
+              )
+            ],
+          ),
+        ),
+        actions: <Widget>[
+          FlatButton(
+            child: Text(tr("Cancel").toUpperCase()),
+            onPressed: () => Navigator.pop(c, false),
+          ),
+          FlatButton(
+            child: Text(tr("OK")),
+            onPressed: widget.controller.text.length >= widget.minLength
+                ? () => Navigator.pop(c, true)
+                : null,
+          ),
+        ],
+      );
+}
+
 /// Show an alert dialog to get user confirmation for something
 ///
 /// Return value of this function is never null