javascript 检查 Angular 指令是否存在
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Check if an Angular directive exists
提问by Monkey34
We're doing a lot of work around dynamic directives in our Angular project, and one thing that came up as a nice-to-have was a way to have a generic directive that can list many different types of similar objects (e.g., messages, users, comments, etc.), by delegating to specific directives based on the objects' types.
我们在 Angular 项目中围绕动态指令做了很多工作，其中一件很高兴的事情是拥有一个通用指令，该指令可以列出许多不同类型的相似对象（例如，消息、用户、评论等），根据对象的类型委托给特定的指令。
We call this directive, object-listand it will hopefully delegate to a number of different directives, if we can get it working properly.
我们称这个指令object-list为，如果我们可以让它正常工作，它有望委托给许多不同的指令。
The main issue we need to tackle is whether or not a directive that this object-listdirective has been provided exists in our system. The way we've been checking this is by issuing a $compileagainst the target directive, linking it to a scope, and checking its HTML contents (e.g., var tmpElement = $compile('<div my-message'></div>')(scope);). This seems to work when the template for the target directive is referenced by the templateoption, but when we instead try to point to a templateUrl, the HTML contents are empty.
我们需要解决的主要问题是object-list我们的系统中是否存在提供该指令的指令。我们一直在检查这一点的方法是$compile针对目标指令发出 a ，将其链接到范围，并检查其 HTML 内容（例如，var tmpElement = $compile('<div my-message'></div>')(scope);）。当目标指令的模板由template选项引用时，这似乎有效，但是当我们尝试指向A时templateUrl，HTML内容为空。
Here's a Plunker, with the templateUrlapproach in place (not working). You can comment it out and uncomment the templateline to see the alert show up.
这是一个Plunker，templateUrl方法已经到位（不起作用）。您可以将其注释掉并取消注释该template行以查看警报显示。
http://plnkr.co/edit/wD4ZspbGSo68v4eRViTp
http://plnkr.co/edit/wD4ZspbGSo68v4eRViTp
Is there another way to check the existence of a directive? I'll admit, this does seem a bit of a hack.
有没有另一种方法来检查指令的存在？我承认，这确实有点像黑客。
回答by Buu Nguyen
You can use $injector.hasto check if a provider or instance exists.
您可以$injector.has用来检查提供者或实例是否存在。
app.directive('objectList', function ($compile, $injector) {
return {
template: 'OK',
link: function (scope, element, attrs) {
var exist = $injector.has('myMessageDirective');
...
}
};
});
