Angular Translate async timing issue with $transla

问题:

I am using the excellent Angular Translate ($translate) directive/service to deal with multiple Locale Languages and since I have multiple locale files I use the convenient $translateProvider.useStaticFilesLoader to load my translation files through a structure of localeAbbr.json, for example en.json, es.json, etc... I built a Plunker to show my open source project and that project uses the locale through Git raw files (pointing to the actual Github repository, meaning not local to the plunker demo). My project is built as a Directive and a Service, I made a small Plunker to show my timing issue with the JSON file loading.

All that to say that it seems $translateProvider.useStaticFilesLoader works asynchronous while I would really need it to be synchronous because by the time the plunker runs, the JSON files are not yet parsed while I already called a $translate.instant() on my messages.

I have a Plunker showing the problem.

And here is part of my quick Service demo:

app.factory('validationService', ['$filter', '$translate', function ($filter, $translate) {
  var service = this;
  var validationSummary = [];
  var errorMessages = [
    'INVALID_ALPHA',
    'INVALID_ALPHA_SPACE',
    'INVALID_ALPHA_NUM',
    'INVALID_BOOLEAN'
  ];

  //var $translate = $filter('translate');

  for(var i=0, ln=errorMessages.length; i < ln; i++) {
    validationSummary.push({  
      field: i,
      message: $translate.instant(errorMessages[i])
    });
  }

  // attach public functions
  service.getValidationSummary = getValidationSummary;
  return service;

  // function declaration
  function getValidationSummary() {
    return validationSummary;
  }
}]);

The $translateProvider configuration

app.config(['$translateProvider', function ($translateProvider) {
  $translateProvider.useStaticFilesLoader({
    prefix: 'https://rawgit.com/ghiscoding/angular-validation/master/locales/validation/',
    suffix: '.json'
    });

    // load English ('en') table on startup
    $translateProvider.preferredLanguage('en').fallbackLanguage('en');
}]);

Call my Service through the Controller:

app.controller("TestController", function($scope, validationService) {
  var vm = this;
  vm.displayValidationSummary = true;

  vm.validationSummary = validationService.getValidationSummary();
});

and finally the HTML using the controller:

<div class="alert alert-danger alert-dismissable" ng-show="vm.displayValidationSummary">
  <button type="button" class="close" data-dismiss="alert" aria-hidden="true" ng-click="displayValidationSummary = false">&times;</button>
  <h4><strong>{{ 'ERRORS' | translate }}!</strong></h4>
  <ul>
      <li ng-repeat="item in vm.validationSummary">{{item.field }}: {{item.message}}</li>
  </ul>
</div>

Since I'm using AngularJS 1.3+, I also found that $translate only gets translated once, so the author suggest to use translateFilter.$stateful = true; and I tried but that doesn't seem to help.

Again here is the Plunker

I have been spending weeks on trying to find and code all kind of solution but I never got it to work and I'm really sad of seeing my raw translation code :(

Please Help!!!

EDIT
I realized that my question was not covering everything related to my problem. On top of the translation delay problem, I also have to pass extra arguments and that is a huge problem passing them to the translation anonymous function. By the time the promise is finished, the state of my arguments have already changed. For example:

$translate(validator.message).then(function(translation) {
    // only log the invalid message in the $validationSummary
    addToValidationSummary(formElmObj, translation);

    // error Display
    if(!isValid) {
      updateErrorMsg(translation, isValid);
    }else if(!!formElmObj && formElmObj.isValid) {
      addToValidationSummary(formElmObj, '');
    }
}, function(data) {
    throw 'Failed to translate' + data;
});

回答1:

When working with AngularJS, or JavaScript for that matter you really need to embrace the asynchronous paradigm. In order to make dealing with asynchronous code less cumbersome you can employ the use of Promises. Angular gives you a service called $q which does the heavy lifting for you

https://docs.angularjs.org/api/ng/service/$q

getting ones head around Promises can take time but well worth the effort in the long run.

Essentially what you need to do with your validationService is to make use of $translate's promise api which will give you the translation you require based on the supplied key when it is in a position to do so. What this boils down to is that you ask $translate for all of the translationId's you wish to get a translation for and when all have been fetched you populate the validationSummary array with your messages.

app.factory('validationService', ['$q', '$translate', function ($q, $translate) {

  var translationsPromises = [], 
    validationSummary = [],
    errorMessages = [
      'INVALID_ALPHA',
      'INVALID_ALPHA_SPACE',
      'INVALID_ALPHA_NUM',
      'INVALID_BOOLEAN'
    ];


  angular.forEach(errorMessages, function(val, key) {
    translationsPromises.push($translate(val));
  });

  $q.all(translationsPromises)
    .then(function(translations) {
      angular.forEach(translations, function(val, key) {
        validationSummary.push({
          filed: key,
          message: val
        });
      });
    })
    .catch(function (err) {
      console.error('Failed to translate error messages for validation summary', err);  
    });

  // function declaration
  function getValidationSummary() {
    return validationSummary;
  }

  return {
    getValidationSummary: getValidationSummary
  };

}]);

I've forked your plunker and modified it to include the above sample

http://plnkr.co/edit/7DCwvY9jloXwfetKtcDA?p=preview

Another observation is that you are using the translate filter in the HTML. Please be aware that this can prove to be expensive if you have a large DOM as Angular will make the call to translate each key on every digest. An approach to consider would be to provide your vm with a labels object and use the $filter service to populate them upon controller instantiation.

回答2:

I found out the answer to my problem of passing extra arguments to the anonymous function of the promise is to use Closures, in this way the variables are the same before the promise and inside it too. So I basically have to wrap my $translate call into the closure, something like the following:

(function(formElmObj, isValid, validator) {
    $translate(validator.message).then(function(translation) {
        message = message.trim();

        // only log the invalid message in the $validationSummary
        addToValidationSummary(formElmObj, message);

        // error Display
        if(!isValid) {
          updateErrorMsg(message, isValid);
        }else if(!!formElmObj && formElmObj.isValid) {
          addToValidationSummary(formElmObj, '');
        }
    }, function(data) {
        throw 'Failed to translate' + data;
    });
})(formElmObj, isValid, validator);

and now finally, my variables are correct and keep the value at that point in time :)

回答3:

While it is true that $translateProvider.useStaticFilesLoader does not return a promise, I looked inside the $translate service and found that it provides a handy callback onReady() which does return a promise. This callback is invoked when the $translate service has finished loading the currently selected language, and is useful for making sure that instant translations will work as expected after page initialization:

$translate.onReady(function () {
    // perform your instant translations here
    var translatedMsg = $translate.instant('INVALID_ALPHA');
});