在不使上下文无效的情况下读取会话变量 [英] Read session variable without invalidating context

问题描述

有没有一种方法可以读取 Session 变量，而无需在模板更改时重新渲染它?

Is there a way to read from a Session variable without re-rendering the template when it changes?

场景:

我使用 jQuery 动态更改元素的样式，但是当创建新元素时，我想设置其默认样式(我知道在呈现元素时我可以调用相同的 jQuery 命令)

I change the style of elements dynamically using jQuery, but when a new element is created I want to set its default style (I know I could call the same jQuery command when the element is rendered)

示例:

<template name="image">
    <!-- How can I avoid -height- being reactive -->
    <img src="img.jpg" style="height: {{height}}">
</template>

Templates.image.height = function() {
    return Session.get("height");
};

Templates.controls.events = {
    'click #btn': function() {
        // Change the height of all exiting images
        $("img").css({height: Session.get("height")});
    }
};

我希望添加的每个新图像都将高度存储在会话变量中，而无需重新渲染 img.我能想到的所有解决方案都像是黑客攻击.

I would like every new image added to have the height stored in the session variable without re-rendering the img. All the solutions I can think of feel like hacks.

推荐答案

Session 将其值存储在 Session.keys 中，但它们是序列化的.要反序列化它们，您可以使用 parse 函数nofollow">https://github.com/meteor/meteor/blob/master/packages/session/session.js:

Session stores its values in Session.keys, but they're serialized. To deserialize them, you can use the parse function from https://github.com/meteor/meteor/blob/master/packages/session/session.js :

var parse = function (serialized) {
  if (serialized === undefined || serialized === 'undefined')
    return undefined;
  return EJSON.parse(serialized);
};

然后，代替 Session.get('key-name')，执行:parse(Session.keys['key-name']).这应该与 Session.get 相同，而不会使任何上下文无效.将所有这些放在一起，这是一种似乎有效的方法:

Then, instead of Session.get('key-name'), do: parse(Session.keys['key-name']). This should do the same as Session.get without invalidating any contexts. Putting all this together, here's an approach that seems to work:

Session._parse = function (serialized) {
  if (serialized === undefined || serialized === 'undefined')
    return undefined;
  return EJSON.parse(serialized);
};

Session.getNonReactive = function (key) {
  var self = this;
  return self._parse(self.keys[key]);
};    

更新 3/13/2013:Meteor 刚刚发布了 v0.5.8，并附带了一个新功能.这是执行此操作的新方法:

UPDATE 3/13/2013: Meteor just released v0.5.8, and with it a new function. Here's the new way to do this:

Session.getNonReactive = function (key) {
  return Deps.nonreactive(function () { return Session.get(key); });
};  

更新 15/2/2016Meter 目前已弃用，但它仍然有效.使用 Tracker 代替:

UPDATE 15/2/2016 Meter is currently deprecated, though it still works. Use Tracker instead:

Session.getNonReactive = function (key) {
  return Tracker.nonreactive(function () { return Session.get(key); });
};  

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