Added digits feature

You can set minimum digits for integer values so that "1" displays as
"01" or "001" depending on the `digits` value.

Author: akhokhlushin

example/lib/main.dart

@@ -48,6 +48,14 @@ class HorizontalSpinBoxPage extends StatelessWidget {
             ),
             padding: const EdgeInsets.all(16),
           ),
+          Padding(
+            child: SpinBox(
+              value: 5,
+              digits: 2,
+              decoration: InputDecoration(labelText: '2 digits'),
+            ),
+            padding: const EdgeInsets.all(16),
+          ),
           Padding(
             child: SpinBox(
               max: 10.0,

lib/src/base_spin_box.dart

@@ -35,6 +35,7 @@ abstract class BaseSpinBox extends StatefulWidget {
   double get step;
   double get value;
   int get decimals;
+  int get digits;
   ValueChanged<double>? get onChanged;
   bool Function(double value)? get canChange;
   VoidCallback? get beforeChange;
@@ -57,7 +58,9 @@ abstract class BaseSpinBoxState<T extends BaseSpinBox> extends State<T> {
       min: widget.min, max: widget.max, decimals: widget.decimals);
 
   static double _parseValue(String text) => double.tryParse(text) ?? 0;
-  String _formatText(double value) => value.toStringAsFixed(widget.decimals);
+  String _formatText(double value) {
+    return value.toStringAsFixed(widget.decimals).padLeft(widget.digits, '0');
+  }
 
   Map<ShortcutActivator, VoidCallback> get bindings {
     return {
@@ -100,7 +103,7 @@ abstract class BaseSpinBoxState<T extends BaseSpinBox> extends State<T> {
     if (v == _value) return;
 
     if (widget.canChange?.call(v) == false) {
-      controller.text = _cachedValue.toStringAsFixed(widget.decimals);
+      controller.text = _formatText(_cachedValue);
       setState(() {
         _value = _cachedValue;
       });

lib/src/cupertino/spin_box.dart

@@ -55,6 +55,7 @@ class CupertinoSpinBox extends BaseSpinBox {
     this.value = 0,
     this.interval = const Duration(milliseconds: 100),
     this.acceleration,
+    this.digits = 0,
     this.decimals = 0,
     bool? enabled,
     this.readOnly = false,
@@ -130,6 +131,12 @@ class CupertinoSpinBox extends BaseSpinBox {
   @override
   final int decimals;
 
+  /// The number of digits used for formatting the value.
+  ///
+  /// Defaults to `0`.
+  @override
+  final int digits;
+
   /// The interval used for auto-incrementing and -decrementing.
   ///
   /// When holding down the increment and decrement buttons, respectively.

lib/src/material/spin_box.dart

@@ -57,6 +57,7 @@ class SpinBox extends BaseSpinBox {
     this.interval = const Duration(milliseconds: 100),
     this.acceleration,
     this.decimals = 0,
+    this.digits = 0,
     bool? enabled,
     this.readOnly = false,
     this.autofocus = false,
@@ -132,6 +133,12 @@ class SpinBox extends BaseSpinBox {
   @override
   final int decimals;
 
+  /// The number of digits used for formatting the value.
+  ///
+  /// Defaults to `0`.
+  @override
+  final int digits;
+
   /// The interval used for auto-incrementing and -decrementing.
   ///
   /// When holding down the increment and decrement buttons, respectively.