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SASS组件开发

SASS预处理器,增加了css所没有的编程能力,带来了前端开发的效率提高,以及扩展了css的编写技巧。

组件开发

设计一个表单提示层(包括成功success,警告warning,错误等状态error)组件,css需要定义基本样式字体(font-)、外内边距(padding,margin)、显示方式(display)、边框(border)以及其他相关的内容,再为单独的状态定义需要的样式。

css组件开发

先定义基本样式,再对每一个状态定义一套样式

<code>.tips { /* 基本颜色设置 */
  padding: 15px;
  margin-bottom: 20px;
  border-radius: 4px;
}

//成功状态
.tips-success{
    background-color: #47a447;
    color: #fff;
}

//警告状态
.tips-warning{
    background-color: #ed9c28;
    color: #fff;
}

//错误状态
.tips-error{
    background-color: #ed9c28;
    color: #fff;
}
</code>

每一种状态文字和边框颜色需要单独设置,稍显繁琐。后期扩展其它状态,如信息info、危险dange等,就是工作成本的提高。幸好SASS提供了编程能力,为我们解决这种担忧,提高了工作效率。

sass组件开发

组件是对数据和方法的简单封装。

变量默认值!default

先来看一段js的变量声明代码

<code>var a = 1;
console.log(a);//1
</code>

再看一段sass代码,是不是很简单。

<code>$color:blue;
$color:red; !default;//变量申明带有!default,表示当前值为缺省值
p{
    color:$color;//输出blue
}
</code>

声明!default,在这里输出blue,很有趣吧。简单说下它的作用:假设变量申明带有!default,表示此变量为默认值,可被全局的普通声明覆盖。这点还不能体现它的伟大作用。

@mixin应用
  • 先声明@mixin
  • 在需要的地方使用@include来声明调用mixins。

    <code>/* mixin */
    @mixin tips($background,$text-color,$tipsStylePadding) {
        background-color: $background;
        color: $text-color;
        padding: $tipsStylePadding;
        margin-bottom: 20px;
        border-radius: 4px;
    }
    </code>

调用功能模块,当前的组件可扩展出多个组件样式。

<code>//成功状态
.tips-success { 
  @include tips($background,$text-color,$tipsStylePadding);
}

//警告状态
.tips-warning {
  @include tips($background,$text-color,$tipsStylePadding);
}

//错误状态
.tips-error {
  @include tips($background,$text-color,$tipsStylePadding);
}

//信息状态(再扩展一个)
.tips-info {
  @include tips($background,$text-color);,$tipsStylePadding
}
</code>

@include在需要的地方随意调用,不够规范,后期难以维护。

组件实例
  • 现在我们新建个scss文件,这里暂且叫做_tips.scss。

    <code>/* 变量
    ---------------------------------*/
    $background:         #47a447 !default;
    $text-color:         #fff !default;
    $tipsStylePadding:   15px !default;
    /* mixin
    ---------------------------------*/
    @mixin tips($background,$text-color,$tipsStylePadding) {
        background-color: $background;
        color: $text-color;
        padding: $tipsStylePadding;
        margin-bottom: 20px;
        border-radius: 4px;
    }
    /*样式
    ---------------------------------*/
    //成功状态
    .tips-success { 
      @include tips($background,$text-color,$tipsStylePadding);
    }
    
    //警告状态
    .tips-warning {
      @include tips($background,$text-color,$tipsStylePadding);
    }
    
    //错误状态
    .tips-error {
      @include tips($background,$text-color,$tipsStylePadding);
    }
    
    //信息状态(再扩展一个)
    .tips-info {
      @include tips($background,$text-color,$tipsStylePadding);
    }
    </code>

接下来我们要在所需要的文件,调用这个文件,这个组件就开发完了

<code>//导入_tpis.scss
@import '_tips';    
</code>

问题?

  • 组件是重复可调用的,也是对数据和方法的简单封装
  • 如果我们对默认的padding为15px不满意,要改为5px,怎么弄

重新覆写

重新覆写,会产生相同的代码,这不是我们想要的组件

<code>//导入_tips.scss
@import '_tips';
.tips-success{
     padding:5px;
}
/*编译后样式
---------------------------------*/
.tips-success{ 
    background-color: #47a447;
    color: #fff;
    padding: 15px;
    margin-bottom: 20px;
    border-radius: 4px;
}
.tips-success{
    padding: 5px;
}
</code>

修改参数

改变@include的参数,同样会产生相同的代码,也不是我们想要的组件

<code>//导入_tips.scss
@import '_tips';
.tips-success{
   @include tips($tipsStyleBorder,5px);
}
/*编译后样式
---------------------------------*/
.tips-success{ 
    background-color: #47a447;
    color: #fff;
    padding: 15px;
    margin-bottom: 20px;
    border-radius: 4px;
}
.tips-success{
    background-color: #47a447;
    color: #fff;
    padding: 5px;
    margin-bottom: 20px;
    border-radius: 4px;
}
</code>

正确解决方法

这里就需要使用 !default;特性

<code>//申明$tpisStylePadding为5px
$tpisStylePadding:  5px;

//导入_tips.scss
@import '_tips';

/*编译后样式
---------------------------------*/
.tips-success {
    background-color: #47a447;
    color: #fff;
    padding: 5px;
    margin-bottom: 20px;
    border-radius: 4px;
}
</code>

变量设计原则

  • 所有变量为默认值,后面加有!default,以方便覆盖;
  • 有些变量为开关变量,值只能是true或false,可以用来表示是否输出样式,应用于兼容及控制代码;
  • 有些变量为复合变量,一个变量会有几个值,以减少变量个数。

参考文档

 

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