number static method

Validator number({ bool allowNull = false, int allowedDecimals = 0, bool allowNegatives = true, })

Creates a validator that checks if a control's value is a valid number.

This validator can be applied to controls with String or num (int, double) values. It provides fine-grained control over what constitutes a valid number:

• allowNull: If true, a null control value is considered valid. Defaults to false.
• allowedDecimals: Specifies the maximum number of digits allowed after the decimal point. Defaults to 0, meaning only integers are allowed. For example, allowedDecimals: 2 would allow numbers like 123.45 or 123.4 but not 123.456.
• allowNegatives: If true, negative numbers (e.g., -10) are considered valid. Defaults to true.

The validation error is exposed under the ValidationMessage.number key. Possible error values include NumberValidatorError.nullValue (if allowNull is false and the value is null), NumberValidatorError.unsignedNumber (if allowNegatives is false and the number is negative), NumberValidatorError.invalidDecimals (if the number of decimal places exceeds allowedDecimals), or NumberValidatorError.invalidNumber (for non-numeric input or invalid formatting).

Examples:

Basic Usage (Integer only, not null, positive):

final control = FormControl<String>(validators: [Validators.number()]);

control.value = '123';
print(control.valid); // true

control.value = '-123';
print(control.valid); // true (allowNegatives is true by default)

control.value = '12.34';
print(control.valid); // false (allowedDecimals is 0 by default)

control.value = 'abc';
print(control.valid); // false

control.value = null;
print(control.valid); // false (allowNull is false by default)

Allowing Decimals:

final decimalControl = FormControl<String>(
  validators: [Validators.number(allowedDecimals: 2)],
);

decimalControl.value = '12.34';
print(decimalControl.valid); // true

decimalControl.value = '12.345';
print(decimalControl.valid); // false (too many decimal places)

decimalControl.value = '12';
print(decimalControl.valid); // true (integers are valid when decimals are allowed)

Disallowing Negative Numbers:

final positiveControl = FormControl<String>(
  validators: [Validators.number(allowNegatives: false)],
);

positiveControl.value = '100';
print(positiveControl.valid); // true

positiveControl.value = '-50';
print(positiveControl.valid); // false

Allowing Null Values:

final nullableControl = FormControl<String>(
  validators: [Validators.number(allowNull: true)],
);

nullableControl.value = null;
print(nullableControl.valid); // true

nullableControl.value = '123';
print(nullableControl.valid); // true

Using with double type controls:

final doubleControl = FormControl<double>(
  validators: [Validators.number(allowedDecimals: 2)],
);

doubleControl.value = 123.45;
print(doubleControl.valid); // true

doubleControl.value = 123.456;
print(doubleControl.valid); // false

Implementation

static Validator<dynamic> number({
  bool allowNull = false,
  int allowedDecimals = 0,
  bool allowNegatives = true,
}) => NumberValidator(
  allowNull: allowNull,
  allowedDecimals: allowedDecimals,
  allowNegatives: allowNegatives,
);