聚合物dom-如果之后会发生什么？
[英]Polymer dom-if what comes after the if?
问题描述
I have a demoMode Boolean property for my element, and I want to display some dummy data when the property is true and live data when it's false . 
我有一个demoMode布尔属性为我的元素，我希望在属性显示一些假数据true和实时数据时，它的false 。
I've tried: 我试过了：
<template dom-if if="{{_isDemo()}}">hello from demo</template>
<template dom-if if="{{_isLive()}}">hello from live</template>
where the functions are just {return this.demoMode;} and {return !(this.demoMode);} . 函数只是{return this.demoMode;}和{return !(this.demoMode);} 。
The live mode seems to always be showing no matter what. 无论如何，现场模式似乎总是显示出来。 I tried using square brackets ( [[]] ), curly brackets ( {{}} ), and even no brackets ( if="_isDemo()" ). 我尝试使用方括号（ [[]] ），大括号（ {{}} ），甚至没有括号（ if="_isDemo()" ）。 Do I need to use them? 我需要使用它们吗？
The way it currently works is there's the app, and there's a demo/index.html that sends the demo-mode attribute like: 它目前的工作方式是应用程序，并且有一个demo/index.html发送demo-mode属性，如：
<my-app demo-mode></my-app>
(I'm open to other ways of doing this, if anyone has input!) （如果有人提出意见，我会采取其他方式做到这一点！）
2 个解决方案
解决方案1
3 2017-03-02 04:44:38
As @montrealist indicated, the if property should evaluate to a Boolean. 正如@montrealist指出的那样， if属性应该计算为布尔值。 The binding does not need to be a Boolean itself; 绑定本身不需要布尔值; it could also be a computed binding / property that returns a Boolean. 它也可以是一个返回布尔值的计算绑定 / 属性 。
You're using a computed binding for the if condition, but the binding is missing a variable dependency (ie, an argument), so it's evaluated only once at initialization. 您正在为if条件使用计算绑定，但绑定缺少变量依赖项（即参数），因此在初始化时仅计算一次。 I assume demoMode has a falsy default value, which would cause _isLive() to always evalulate to true . 我假设demoMode有一个虚假的默认值，这将导致_isLive()始终评估为true 。
Since _isDemo() and _isLive() both depend on this.demoMode , your computed binding should be _isDemo(demoMode) and _isLive(demoMode) , respectively: 由于_isDemo()和_isLive()都依赖于this.demoMode ，因此您的计算绑定应分别为_isDemo(demoMode)和_isLive(demoMode) ：
HTMLImports.whenReady(() => { Polymer({ is: 'x-foo', properties: { demoMode: { type: Boolean, value: false } }, _isDemo: function(demo) { return demo; }, _isLive: function(demo) { return !demo; }, _toggleDemo: function() { this.demoMode = !this.demoMode; } }); });
<head> <base href="https://polygit.org/polymer+1.8.1/components/"> <script src="webcomponentsjs/webcomponents-lite.js"></script> <link rel="import" href="polymer/polymer.html"> </head> <body> <x-foo></x-foo> <dom-module id="x-foo"> <template> <button on-tap="_toggleDemo">Toggle Demo Mode</button> <template is="dom-if" if="{{_isDemo(demoMode)}}"> <h1>Demo Mode</h1> </template> <template is="dom-if" if="{{_isLive(demoMode)}}"> <h1>Live Mode</h1> </template> </template> </dom-module> </body>
I tried using square brackets (
[[]]), curly brackets ({{}}), and even no brackets (if="_isDemo()").[[]]），大括号（{{}}），甚至没有括号（if="_isDemo()"）。 Do I need to use them?
Yes, you need them. 是的，你需要它们。 Data bindings (including computed bindings) require the brackets (either square or curly). 数据绑定（包括计算绑定）需要括号（方形或卷曲）。 Normally, the curly brackets indicate a two-way data binding, while the square ones indicate one-way. 通常，大括号表示双向数据绑定，而方形表示单向。 For computed bindings, they both have the same effect. 对于计算绑定，它们都具有相同的效果。
解决方案2
1 2017-03-02 02:34:40
I don't think you can pass a function into the if . 我不认为你可以将函数传递给if 。 The API specifically mentions a boolean . API 专门提到了一个布尔值 。 From doc: 来自doc：
Elements can be conditionally stamped based on a boolean property by wrapping them in a custom HTMLTemplateElement type extension called dom-if
Just stick to properties. 坚持住房产。 Also, your syntax may be based on an older version of Polymer. 此外，您的语法可能基于旧版本的Polymer。 You need to declare the conditional template like so: 您需要声明条件模板，如下所示：
<template is="dom-if" if="{{demo}}">hello from demo!</template>
Here's a working plunkr (all the logic is inside name-tag.html ). 这是一个有效的plunkr （所有逻辑都在name-tag.html ）。
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