表单

概述

🌐 Overview

Bootstrap 的表单控件通过类扩展了我们重新设计的表单样式。使用这些类可以选择使用它们的自定义显示，从而在不同浏览器和设备上实现更一致的渲染效果。

🌐 Bootstrap’s form controls expand on our Rebooted form styles with classes. Use these classes to opt into their customized displays for a more consistent rendering across browsers and devices.

请确保在所有输入字段上使用适当的 type 属性（例如，电子邮件地址使用 email 或数字信息使用 number），以利用诸如电子邮件验证、数字选择等更新的输入控件。

🌐 Be sure to use an appropriate type attribute on all inputs (e.g., email for email address or number for numerical information) to take advantage of newer input controls like email verification, number selection, and more.

这里有一个快速示例来演示 Bootstrap 的表单样式。继续阅读以获取有关必需类、表单布局等的文档。

🌐 Here’s a quick example to demonstrate Bootstrap’s form styles. Keep reading for documentation on required classes, form layout, and more.

<form>
  <div class="mb-3">
    <label for="exampleInputEmail1" class="form-label">Email address</label>
    <input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp">
    <div id="emailHelp" class="form-text">We'll never share your email with anyone else.</div>
  </div>
  <div class="mb-3">
    <label for="exampleInputPassword1" class="form-label">Password</label>
    <input type="password" class="form-control" id="exampleInputPassword1">
  </div>
  <div class="mb-3 form-check">
    <input type="checkbox" class="form-check-input" id="exampleCheck1">
    <label class="form-check-label" for="exampleCheck1">Check me out</label>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

禁用表格

🌐 Disabled forms

在输入框上添加 disabled 布尔属性以防止用户交互并使其看起来更淡。

🌐 Add the disabled boolean attribute on an input to prevent user interactions and make it appear lighter.

<input class="form-control" id="disabledInput" type="text" placeholder="Disabled input here..." disabled>

向 <fieldset> 添加 disabled 属性以禁用其中的所有控件。浏览器会将 <fieldset disabled> 内的所有原生表单控件（<input>、<select> 和 <button> 元素）视为禁用，从而阻止这些控件的键盘和鼠标交互。

🌐 Add the disabled attribute to a <fieldset> to disable all the controls within. Browsers treat all native form controls (<input>, <select>, and <button> elements) inside a <fieldset disabled> as disabled, preventing both keyboard and mouse interactions on them.

然而，如果你的表单还包括类似按钮的自定义元素，例如 <a class="btn btn-*">...</a>，这些元素将只被赋予 pointer-events: none 样式，这意味着它们仍然可以通过键盘获得焦点并操作。在这种情况下，你必须通过添加 tabindex="-1" 来手动修改这些控件，以防止它们获得焦点，并添加 aria-disabled="disabled" 来向辅助技术指示它们的状态。

🌐 However, if your form also includes custom button-like elements such as <a class="btn btn-*">...</a>, these will only be given a style of pointer-events: none, meaning they are still focusable and operable using the keyboard. In this case, you must manually modify these controls by adding tabindex="-1" to prevent them from receiving focus and aria-disabled="disabled" to signal their state to assistive technologies.

<form>
  <fieldset disabled>
    <legend>Disabled fieldset example</legend>
    <div class="mb-3">
      <label for="disabledTextInput" class="form-label">Disabled input</label>
      <input type="text" id="disabledTextInput" class="form-control" placeholder="Disabled input">
    </div>
    <div class="mb-3">
      <label for="disabledSelect" class="form-label">Disabled select menu</label>
      <select id="disabledSelect" class="form-select">
        <option>Disabled select</option>
      </select>
    </div>
    <div class="mb-3">
      <div class="form-check">
        <input class="form-check-input" type="checkbox" id="disabledFieldsetCheck" disabled>
        <label class="form-check-label" for="disabledFieldsetCheck">
          Can’t check this
        </label>
      </div>
    </div>
    <button type="submit" class="btn btn-primary">Submit</button>
  </fieldset>
</form>

无障碍

🌐 Accessibility

确保所有表单控件都有适当的可访问名称，以便将其用途传达给辅助技术的用户。实现这一点的最简单方法是使用 <label> 元素，或者在按钮的情况下，在 <button>...</button> 内容中包含足够描述性的文本。

🌐 Ensure that all form controls have an appropriate accessible name so that their purpose can be conveyed to users of assistive technologies. The simplest way to achieve this is to use a <label> element, or—in the case of buttons—to include sufficiently descriptive text as part of the <button>...</button> content.

在无法包含可见的 <label> 或适当文本内容的情况下，仍然有提供可访问名称的替代方法，例如：

🌐 For situations where it’s not possible to include a visible <label> or appropriate text content, there are alternative ways of still providing an accessible name, such as:

• <label> 元素使用 .visually-hidden 类被隐藏
• 使用 aria-labelledby 指向可以作为标签的现有元素
• 提供 title 属性
• 使用 aria-label 明确设置元素的可访问名称

如果这些都不存在，辅助技术可能会使用 placeholder 属性作为 <input> 和 <textarea> 元素可访问名称的备用方法。本节的示例提供了一些建议的、特定情况的做法。

🌐 If none of these are present, assistive technologies may resort to using the placeholder attribute as a fallback for the accessible name on <input> and <textarea> elements. The examples in this section provide a few suggested, case-specific approaches.

虽然使用视觉上隐藏的内容（.visually-hidden、aria-label，甚至 placeholder 内容，一旦表单字段有内容就会消失）对辅助技术用户有好处，但对于某些用户来说，缺乏可见的标签文本仍可能是一个问题。通常，某种形式的可见标签是最佳的方法，这对于可访问性和可用性都是如此。

🌐 While using visually hidden content (.visually-hidden, aria-label, and even placeholder content, which disappears once a form field has content) will benefit assistive technology users, a lack of visible label text may still be problematic for certain users. Some form of visible label is generally the best approach, both for accessibility and usability.

CSS

许多表单变量在通用层级上设置，以便由各个表单组件重复使用和扩展。你最常看到这些变量的形式是 $input-btn-* 和 $input-* 变量。

🌐 Many form variables are set at a general level to be re-used and extended by individual form components. You’ll see these most often as $input-btn-* and $input-* variables.

Sass 变量

🌐 Sass variables

$input-btn-* 变量是在我们的 按钮 和表单组件之间共享的全局变量。你会发现这些变量经常被重新分配为其他组件特定变量的值。

$input-btn-padding-y:         .375rem;
$input-btn-padding-x:         .75rem;
$input-btn-font-family:       null;
$input-btn-font-size:         $font-size-base;
$input-btn-line-height:       $line-height-base;

$input-btn-focus-width:         $focus-ring-width;
$input-btn-focus-color-opacity: $focus-ring-opacity;
$input-btn-focus-color:         $focus-ring-color;
$input-btn-focus-blur:          $focus-ring-blur;
$input-btn-focus-box-shadow:    $focus-ring-box-shadow;

$input-btn-padding-y-sm:      .25rem;
$input-btn-padding-x-sm:      .5rem;
$input-btn-font-size-sm:      $font-size-sm;

$input-btn-padding-y-lg:      .5rem;
$input-btn-padding-x-lg:      1rem;
$input-btn-font-size-lg:      $font-size-lg;

$input-btn-border-width:      var(--#{$prefix}border-width);