feat(validators): maxLength and minLength can now validate Iterable values length

Author: danvick

packages/form_builder_validators/lib/src/form_builder_validators.dart

@@ -111,15 +111,20 @@ class FormBuilderValidators {
 
   /// [FormFieldValidator] that requires the length of the field's value to be
   /// greater than or equal to the provided minimum length.
-  static FormFieldValidator<String> minLength(
+  static FormFieldValidator<T> minLength<T>(
     BuildContext context,
     int minLength, {
     bool allowEmpty = false,
     String? errorText,
   }) {
     assert(minLength > 0);
-    return (valueCandidate) {
-      final valueLength = valueCandidate?.length ?? 0;
+    return (T? valueCandidate) {
+      assert(valueCandidate is String ||
+          valueCandidate is Iterable ||
+          valueCandidate == null);
+      var valueLength = 0;
+      if (valueCandidate is String) valueLength = valueCandidate.length;
+      if (valueCandidate is Iterable) valueLength = valueCandidate.length;
       return valueLength < minLength && (!allowEmpty || valueLength > 0)
           ? errorText ??
               FormBuilderLocalizations.of(context).minLengthErrorText(minLength)
@@ -129,17 +134,24 @@ class FormBuilderValidators {
 
   /// [FormFieldValidator] that requires the length of the field's value to be
   /// less than or equal to the provided maximum length.
-  static FormFieldValidator<String> maxLength(
+  static FormFieldValidator<T> maxLength<T>(
     BuildContext context,
     int maxLength, {
     String? errorText,
   }) {
     assert(maxLength > 0);
-    return (valueCandidate) => null != valueCandidate &&
-            valueCandidate.length > maxLength
-        ? errorText ??
-            FormBuilderLocalizations.of(context).maxLengthErrorText(maxLength)
-        : null;
+    return (T? valueCandidate) {
+      assert(valueCandidate is String ||
+          valueCandidate is Iterable ||
+          valueCandidate == null);
+      var valueLength = 0;
+      if (valueCandidate is String) valueLength = valueCandidate.length;
+      if (valueCandidate is Iterable) valueLength = valueCandidate.length;
+      return null != valueCandidate && valueLength > maxLength
+          ? errorText ??
+              FormBuilderLocalizations.of(context).maxLengthErrorText(maxLength)
+          : null;
+    };
   }
 
   /// [FormFieldValidator] that requires the field's value to be a valid email address.

packages/form_builder_validators/test/form_builder_validators_test.dart

@@ -104,9 +104,10 @@ void main() {
           }));
 
   testWidgets(
-      'FormBuilderValidators.maxLength',
+      'FormBuilderValidators.maxLength for String',
       (WidgetTester tester) => testValidations(tester, (context) {
-            final validator = FormBuilderValidators.maxLength(context, 5);
+            final validator =
+                FormBuilderValidators.maxLength<String>(context, 5);
             // Pass
             expect(validator(null), isNull);
             expect(validator(''), isNull);
@@ -116,10 +117,12 @@ void main() {
             expect(validator('something long'), isNotNull);
             expect(validator('123456'), isNotNull);
           }));
+
   testWidgets(
-      'FormBuilderValidators.minLength',
+      'FormBuilderValidators.minLength for String',
       (WidgetTester tester) => testValidations(tester, (context) {
-            final validator = FormBuilderValidators.minLength(context, 5);
+            final validator =
+                FormBuilderValidators.minLength<String>(context, 5);
             // Pass
             expect(validator('12345'), isNull);
             expect(validator('123456'), isNull);
@@ -129,11 +132,45 @@ void main() {
             expect(validator(''), isNotNull);
             expect(validator('two'), isNotNull);
             // Advanced
-            final validatorAllowEmpty =
-                FormBuilderValidators.minLength(context, 5, allowEmpty: true);
+            final validatorAllowEmpty = FormBuilderValidators.minLength<String>(
+                context, 5,
+                allowEmpty: true);
             expect(validatorAllowEmpty(null), isNull);
             expect(validatorAllowEmpty(''), isNull);
           }));
+  testWidgets(
+      'FormBuilderValidators.maxLength for Iterable',
+          (WidgetTester tester) => testValidations(tester, (context) {
+        final validator =
+        FormBuilderValidators.maxLength<Iterable<String>>(context, 3);
+        // Pass
+        expect(validator(null), isNull);
+        expect(validator([]), isNull);
+        expect(validator(['one', 'two']), isNull);
+        expect(validator(['one', 'two', 'three']), isNull);
+        // Fail
+        expect(validator(['one', 'two', 'three', 'four']), isNotNull);
+      }));
+
+  testWidgets(
+      'FormBuilderValidators.minLength for Iterable',
+          (WidgetTester tester) => testValidations(tester, (context) {
+        final validator =
+        FormBuilderValidators.minLength<Iterable<String>>(context, 3);
+        // Pass
+        expect(validator(['one', 'two', 'three']), isNull);
+        expect(validator(['one', 'two', 'three', 'four']), isNull);
+        // Fail
+        expect(validator(null), isNotNull);
+        expect(validator([]), isNotNull);
+        expect(validator(['one', 'two']), isNotNull);
+        // Advanced
+        final validatorAllowEmpty = FormBuilderValidators.minLength<Iterable<String>>(
+            context, 3,
+            allowEmpty: true);
+        expect(validatorAllowEmpty(null), isNull);
+        expect(validatorAllowEmpty([]), isNull);
+      }));
 
   testWidgets(
       'FormBuilderValidators.email',