Angular JS - 指令中的数据绑定不起作用

Question

I have an issue with a data binding inside a directive, which call another directive.

Here is the main directive :

var app = angular.module('app');

app.directive("myMainDirective", function ($http) {
return {
    scope: {
        paramId: '='
    },
    link: function (scope) {
        $http.get('some/url/' + scope.paramId+ '.json'
        ).success(function (data) {
                scope.idFromServer = data;
            });
    },
    template: '<span other-directive id="idFromServer"></span>'
}
});

Here is the other directive :

var app = angular.module('app');

app.directive("otherDirective", ['$http', function(http) {
return {
    template: "<span>{{name}}</span>",
    scope: {
        id: "="
    },
    link: function(scope) {
        http.get('another/url/' + scope.id + '.json').then(function(result) {
            scope.name = result.data.name;
        }, function(err) {
            scope.name = "unknown";
        });
    }
}
}])

And the html code wich call the main directive :

<span my-main-directive param-id="myObject.id"></span>

When calling "other-directive", the "idFromServer" is not bind, and is "undefined", so it results to diplay "undefined".

I'm probably missing something stupid, but I don't see what ... (My piece of code is probabley not the best, I'm pretty new to angularjs, and specially the directives, and I tried a lot of ways to accomplish what I want.)

Answer 1

Per my comments, here's one way that might work, using a scope.$watch:

scope.$watch('id', function(id) {
    $http.get('some/url/' + id + '.json')
        .success(function (data) {
            scope.idFromServer = data;
        });
};

This would go inside the link function on the nested directive.

Answer 2

One of the way I'd suggest is don't use two way( = ) binding on idFromServer variable, use {{idFromServer}} Interpolation directive to assign value to attribute, & then use $attr.$observe it will call when interpolation is evaluated.

myMainDirective

app.directive("myMainDirective", function ($http) {
return {
    scope: {
        paramId: '='
    },
    link: function (scope) {
        $http.get('some/url/' + scope.paramId+ '.json'
        ).success(function (data) {
                scope.idFromServer = data;
            });
    },
    template: '<span other-directive id="{{idFromServer}}"></span>'
}
});

otherDirective

app.directive("otherDirective", ['$http', function(http) {
    return {
        template: "<span>{{name}}</span>",
        scope: true, //isolated scope
        link: function(scope, element, attr) {
            attr.$observe(attr.id, function(newVal) {
                http.get('another/url/' + newVal + '.json').then(function(result) {
                    scope.name = result.data.name;
                }, function(err) {
                    scope.name = "unknown";
                });
            });
        }
    }
}])

Answer 3

Since javascript is asynchronous, your two ajax requests are running at basically the same time and id is undefined when the request in other-directive runs.

If you want to try testing this, just set a default value for idFromServer . The request in other-directive will run with the default value.

EDIT: in response to your comment, that is quite a broad question and there are many solutions. The best answer I can give you is simply, never ever run any logic in your link function, just define the directive's behavior and properties - that's what the link function is for. The template is used right away and you can't change that.

In this case, you could get the data prepared in a parent scope and pass the data in attributes.