Add IntTextInputFormatter

stevia/lib/src/widgets/foundation/text_input_formatters.dart

@@ -0,0 +1,54 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:sugar/sugar.dart';
+import 'dart:math' as math;
+
+/// A [IntTextInputFormatter] validates whether the text being edited is an integer in a given [Range].
+///
+/// There is **no** guarantee that the text being edited is an integer since it may be empty or `-`.
+///
+/// Empty text and a single `-` are ignored. Furthermore, a [IntTextInputFormatter] trims all commas separating parts of
+/// the integer, and leading and trailing whitespaces. For example, both ` ` and `-` are allowed while ` 1,000 ` is trimmed
+/// to `1000`.
+///
+///
+/// It is recommended to use set the enclosing [TextField]'s `keyboardType` to [TextInputType.number].
+///
+/// ```dart
+/// TextField(
+///   keyboardType: TextInputType.number,
+///   inputFormatters: [ IntTextInputFormatter(Interval.closedOpen(0, 5)) ], // 0 <= value < 5
+/// );
+/// ```
+class IntTextInputFormatter extends TextInputFormatter {
+  final Range<int> _range;
+
+  /// Creates a [IntTextInputFormatter] in the given [Range].
+  IntTextInputFormatter(this._range): super();
+
+  @override
+  TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue) {
+    if (newValue.text.isEmpty || newValue.text == '-') {
+      return newValue;
+    }
+
+    final trimmed = newValue.text.trim().replaceAll(',', '');
+    return switch (int.tryParse(trimmed)) {
+      final value? when _range.contains(value) => switch (newValue.text.length == trimmed.length) {
+        true => newValue,
+        false => TextEditingValue(
+          text: trimmed,
+          selection: newValue.selection.copyWith(
+            baseOffset: math.min(newValue.selection.start, trimmed.length),
+            extentOffset: math.min(newValue.selection.end, trimmed.length),
+          ),
+          composing: !newValue.composing.isCollapsed && trimmed.length > newValue.composing.start ? TextRange(
+            start: newValue.composing.start,
+            end: math.min(newValue.composing.end, trimmed.length),
+          ): TextRange.empty,
+        )
+      },
+      _ => oldValue,
+    };
+  }
+}

stevia/lib/widgets.dart

@@ -13,9 +13,10 @@
 /// * [StreamValueBuilder]
 ///
 /// ## Foundation
-/// General-purpose widgets.
+/// General-purpose widgets and Flutter services.
 ///
 /// * [ColorFilters]
+/// * [IntTextInputFormatter]
 ///
 /// ## Resizable
 /// Widgets that contain children which can be resized either horizontally or vertically.
@@ -38,6 +39,7 @@ export 'src/widgets/async/future/future_builder.dart' show
 export 'src/widgets/async/stream_value_builder.dart';
 
 export 'src/widgets/foundation/color_filters.dart' hide Matrix5;
+export 'src/widgets/foundation/text_input_formatters.dart';
 
 export 'src/widgets/resizable/resizable_box.dart';
 export 'src/widgets/resizable/resizable_icon.dart';

stevia/test/src/widgets/foundation/text_input_formatters_test.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/material.dart' hide Interval;
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:stevia/stevia.dart';
+import 'package:sugar/sugar.dart';
+
+void main() {
+  group('IntTextInputFormatter', () {
+    late Widget widget;
+
+    setUp(() => widget = MaterialApp(
+      home: Scaffold(
+        body: TextField(
+          keyboardType: TextInputType.number,
+          inputFormatters: [ IntTextInputFormatter(Interval.closedOpen(-50, 50)) ],
+        ),
+      )
+    ));
+
+    for (final (actual, expected) in [
+      ('-50', '-50'),
+      ('-51', ''),
+      ('49', '49'),
+      ('50', ''),
+      ('-', '-'),
+      ('0.0', ''),
+      ('  0   ', '0'),
+      ('1,0', '10'),
+      ('  1,0 ', '10'),
+    ]) {
+      testWidgets('values', (tester) async {
+        await tester.pumpWidget(widget);
+        await tester.enterText(find.byType(TextField), actual);
+
+        expect(find.text(expected), findsOneWidget);
+      });
+    }
+
+    testWidgets('empty string', (tester) async {
+      await tester.pumpWidget(widget);
+      await tester.enterText(find.byType(TextField), '1');
+      await tester.enterText(find.byType(TextField), '');
+
+      expect(find.text(''), findsOneWidget);
+    });
+  });
+}