An observable, computed objects written in Dart with built-in validation


  obsobject: ^1.3.0


An object will notify to all listeners/observers after its value changed.


var a = Observable('test');
a.listen(() {
a.value = 'First test';

Output result:
First test


It's an observable too, but its value will be calculated from other observable object.
It's smart to know which observable object that it's depend on, and auto rebuild value when value of dependencies has changed.


var a = Observable(false);
var b = Observable(1);
var c = Computed(() => a.value ? b.value*10 : 0);

print(c.value); //result 0, depend on only 'a';
b.value = 2;
print(c.value); //result 0, depend on only 'a'
print(c.value);//result 20, depend on 'a', 'b'

Computed object is only recalculate if there are listeners on it or when access to its value.
And the calculation is a async process, so observable can change value many times, but Computed just run one


var a = Observable(0);
var b = Computed(() => a.value);
for(var i=0; i<1000; i++) a.value=i;
print(b.rebuildCount); //result 1

Computed is just give readonly value, thus there are an object Commission used to read+write value


Built-in validate:

  • required: value can not null, empty string, zero
  • email: value must be valid email address
  • range: check number value, string length, array length
  • pattern: check string matched RegExp
  • contains: value must in array
  • unique: value not exist in array
  • true: value must be true
  • custom: check value by a custom function
  • async: check value by a async function
  • all: combine and check all validators
  • least: combine and check all validators but it stopped at the first invalid
  • not: negative a validator
  • async: validate value by an async process

Observable has a property valid error validStatus, they're observables value of validation status.

Validator also has features:

  • condition: used to check something before execute validate
  • message: custom message, default message, support for localize
  • And easy way to custom or extends new validation


//use with Validator....
var email = Observable('',
            validator: ValidatorLeast([ValidatorRequired(), ValidatorEmail()])

//use with Map data config
var email = Observable('',
            validator: Validator.convert({
'least': {
    'validators': {'required': 'Email is required', 'email': true}
//current status
//current invalid message
//listen on validation
email.listen(() {
  if (email.valid) {
    //do something

Flutter widget

  • Create a statefull widget to update UI when observable change value, take look a sample here

  • Or use StreamBuilder with observable.stream

    //observable defined in model layer or global
    final count = Observable(0);
    //in build context of widget
      builder: ...,
      stream: count.stream,

View more details in Wiki, API