Add default

Author: martijn00

CHANGELOG.md

@@ -43,6 +43,7 @@
 * Add unique
 * Add ISBN
 * Add singleLine
+* Add defaultValue
 
 ## 10.0.1
 * Fix regression (include l10n files)

README.md

@@ -55,6 +55,7 @@ Available built-in helper validators:
 - `FormBuilderValidators.aggregate()` - runs the validators in parallel, collecting all errors.
 - `FormBuilderValidators.log()` - runs the validator and logs the value at a specific point in the validation chain.
 - `FormBuilderValidators.skipWhen()` - runs the validator and skips the validation when a certain condition is met.
+- `FormBuilderValidators.defaultValue()` - runs the validator using the default value when the provided value is null.
 
 Available built-in type validators include:
 

lib/src/form_builder_validators.dart

@@ -119,6 +119,14 @@ class FormBuilderValidators {
     };
   }
 
+  /// [FormFieldValidator] that transforms the value to a default if it's null or empty before running the validator.
+  /// * [defaultValue] is the default value to transform to.
+  /// * [validator] is the validator to apply.
+  static FormFieldValidator<T> defaultValue<T>(
+    T defaultValue,
+    FormFieldValidator<T> validator,
+  ) => (valueCandidate) => validator(valueCandidate ?? defaultValue);
+
   /// [FormFieldValidator] that requires the field have a non-empty value.
   /// * [errorText] is the error message to display when the value is empty
   static FormFieldValidator<T> required<T>({

test/form_builder_validators_test.dart

@@ -1208,4 +1208,17 @@ void main() {
       expect(validator('The quick brown fox\n\rjumps'), isNotNull);
     }),
   );
+
+    testWidgets(
+    'FormBuilderValidators.defaultValue',
+    (WidgetTester tester) => testValidations(tester, (context) {
+      final validator = FormBuilderValidators.defaultValue<String>('default', FormBuilderValidators.alphabetical());
+      // Pass
+      expect(validator(null), isNull);
+      expect(validator('hello'), isNull);
+      // Fail
+      expect(validator('123'), isNotNull);
+      expect(validator(''), isNotNull);
+    }),
+  );
 }