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验证器（Validation）

通过浏览器默认行为或自定义样式和 JavaScript，通过 HTML5 表单验证向用户提供有价值的、可操作的反馈。

当前页
我们知道，目前无法访问客户端自定义验证样式和工具提示，因为它们未向辅助技术公开。在我们处理解决方案时，我们建议使用服务器端选项或默认浏览器验证方法。

工作原理

以下是表单验证器与 Bootstrap 的工作原理：

  • HTML表单验证器通过CSS的两个伪类 :invalid和 :valid来使用。它适用于<input>、<select>和<textarea>元素。
  • Bootstrap 将:invalid和 :valid 样式的范围限定为 .was-validated父类，通常应用于 <form>。否则，任何没有值的必填字段在页面加载时都会显示为无效。这样，您可以选择何时激活它们（通常在尝试提交表单后）。
  • 要重置表单的外观（例如，在使用 Ajax 进行动态表单提交的情况下），请在提交后再次从<form>中删除.was-validated类。
  • 作为回调，可以使用.is-invalid和.is-valid类代替服务器端验证的伪类。它们不需要 .was-validated父类。
  • 由于 CSS 工作方式的限制，如果没有自定义 JavaScript 的帮助，我们（目前）无法将样式应用于 DOM 中表单控件之前的 <label> 。
  • 所有现代浏览器都支持约束验证API，这是一系列用于验证表单控件的JavaScript方法。
  • 反馈消息可能会使用 浏览器默认值（每个浏览器都不同，并且无法通过 CSS 设置样式）或我们的自定义反馈样式以及其他 HTML 和 CSS。
  • 您可以在 JavaScript 中提供带有setCustomValidity的自定义有效性消息。

考虑到这一点，请考虑以下有关自定义表单验证样式、可选服务器端类和浏览器默认值的演示。

自定义样式

对于自定义Bootstrap表单验证消息，您需要将 novalidate 布尔属性添加到<form>。这将禁用浏览器默认反馈工具提示，但仍提供对 JavaScript 中表单验证 API 的访问。尝试提交下面的表格;我们的 JavaScript 将拦截提交按钮并将反馈传递给您。尝试提交时，您将看到应用于表单控件的 :invalid和:valid样式。

自定义反馈样式应用自定义颜色、边框、焦点样式和背景图标，以更好地传达反馈。<select>背景图标仅适用于.form-select，而不适用于.form-control。

Looks good!
Looks good!
@
Please choose a username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.
You must agree before submitting.
html 
<form class="row g-3 needs-validation" novalidate>
  <div class="col-md-4">
    <label for="validationCustom01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationCustom01" value="Mark" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationCustom02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationCustom02" value="Otto" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationCustomUsername" class="form-label">Username</label>
    <div class="input-group has-validation">
      <span class="input-group-text" id="inputGroupPrepend">@</span>
      <input type="text" class="form-control" id="validationCustomUsername" aria-describedby="inputGroupPrepend" required>
      <div class="invalid-feedback">
        Please choose a username.
      </div>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationCustom03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationCustom03" required>
    <div class="invalid-feedback">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationCustom04" class="form-label">State</label>
    <select class="form-select" id="validationCustom04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div class="invalid-feedback">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationCustom05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationCustom05" required>
    <div class="invalid-feedback">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input" type="checkbox" value="" id="invalidCheck" required>
      <label class="form-check-label" for="invalidCheck">
        Agree to terms and conditions
      </label>
      <div class="invalid-feedback">
        You must agree before submitting.
      </div>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>
// Example starter JavaScript for disabling form submissions if there are invalid fields
(() => {
  'use strict'

  // Fetch all the forms we want to apply custom Bootstrap validation styles to
  const forms = document.querySelectorAll('.needs-validation')

  // Loop over them and prevent submission
  Array.from(forms).forEach(form => {
    form.addEventListener('submit', event => {
      if (!form.checkValidity()) {
        event.preventDefault()
        event.stopPropagation()
      }

      form.classList.add('was-validated')
    }, false)
  })
})()

浏览器默认值（Browser defaults）

对自定义验证反馈消息或编写 JavaScript 来更改表单行为不感兴趣？一切都很好，您可以使用浏览器默认值。尝试提交下面的表格。根据您的浏览器和操作系统，您会看到略有不同的反馈风格。

虽然这些反馈样式不能用 CSS 设置样式，但您仍然可以通过 JavaScript 自定义反馈文本。

@
html 
<form class="row g-3">
  <div class="col-md-4">
    <label for="validationDefault01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationDefault01" value="Mark" required>
  </div>
  <div class="col-md-4">
    <label for="validationDefault02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationDefault02" value="Otto" required>
  </div>
  <div class="col-md-4">
    <label for="validationDefaultUsername" class="form-label">Username</label>
    <div class="input-group">
      <span class="input-group-text" id="inputGroupPrepend2">@</span>
      <input type="text" class="form-control" id="validationDefaultUsername" aria-describedby="inputGroupPrepend2" required>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationDefault03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationDefault03" required>
  </div>
  <div class="col-md-3">
    <label for="validationDefault04" class="form-label">State</label>
    <select class="form-select" id="validationDefault04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
  </div>
  <div class="col-md-3">
    <label for="validationDefault05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationDefault05" required>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input" type="checkbox" value="" id="invalidCheck2" required>
      <label class="form-check-label" for="invalidCheck2">
        Agree to terms and conditions
      </label>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

服务端（Server-side）

我们建议使用客户端验证，但如果您需要服务器端验证，您可以使用.is-invalid和.is-valid指示无效和有效的表单字段。请注意，这些类也支持.invalid-feedback。

对于无效字段，请确保使用 aria-describedby将无效反馈/错误消息与相关表单字段相关联（请注意，此属性允许引用多个id，以防该字段已指向其他表单文本）。

要修复 边框半径问题，输入组需要一个额外的 .has-validation类。

Looks good!
Looks good!
@
Please choose a username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.
You must agree before submitting.
html 
<form class="row g-3">
  <div class="col-md-4">
    <label for="validationServer01" class="form-label">First name</label>
    <input type="text" class="form-control is-valid" id="validationServer01" value="Mark" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationServer02" class="form-label">Last name</label>
    <input type="text" class="form-control is-valid" id="validationServer02" value="Otto" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationServerUsername" class="form-label">Username</label>
    <div class="input-group has-validation">
      <span class="input-group-text" id="inputGroupPrepend3">@</span>
      <input type="text" class="form-control is-invalid" id="validationServerUsername" aria-describedby="inputGroupPrepend3 validationServerUsernameFeedback" required>
      <div id="validationServerUsernameFeedback" class="invalid-feedback">
        Please choose a username.
      </div>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationServer03" class="form-label">City</label>
    <input type="text" class="form-control is-invalid" id="validationServer03" aria-describedby="validationServer03Feedback" required>
    <div id="validationServer03Feedback" class="invalid-feedback">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationServer04" class="form-label">State</label>
    <select class="form-select is-invalid" id="validationServer04" aria-describedby="validationServer04Feedback" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div id="validationServer04Feedback" class="invalid-feedback">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationServer05" class="form-label">Zip</label>
    <input type="text" class="form-control is-invalid" id="validationServer05" aria-describedby="validationServer05Feedback" required>
    <div id="validationServer05Feedback" class="invalid-feedback">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input is-invalid" type="checkbox" value="" id="invalidCheck3" aria-describedby="invalidCheck3Feedback" required>
      <label class="form-check-label" for="invalidCheck3">
        Agree to terms and conditions
      </label>
      <div id="invalidCheck3Feedback" class="invalid-feedback">
        You must agree before submitting.
      </div>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

支持的元素

验证样式可用于以下窗体控件和组件：

  • 带有 .form-control的 <input>和 <textarea>（在输入组中最多包含一个.form-control）
  • 带有 .form-select的<select>
  • .form-check
Please enter a message in the textarea.
Example invalid feedback text
More example invalid feedback text
Example invalid select feedback
Example invalid form file feedback
html 
<form class="was-validated">
  <div class="mb-3">
    <label for="validationTextarea" class="form-label">Textarea</label>
    <textarea class="form-control" id="validationTextarea" placeholder="Required example textarea" required></textarea>
    <div class="invalid-feedback">
      Please enter a message in the textarea.
    </div>
  </div>

  <div class="form-check mb-3">
    <input type="checkbox" class="form-check-input" id="validationFormCheck1" required>
    <label class="form-check-label" for="validationFormCheck1">Check this checkbox</label>
    <div class="invalid-feedback">Example invalid feedback text</div>
  </div>

  <div class="form-check">
    <input type="radio" class="form-check-input" id="validationFormCheck2" name="radio-stacked" required>
    <label class="form-check-label" for="validationFormCheck2">Toggle this radio</label>
  </div>
  <div class="form-check mb-3">
    <input type="radio" class="form-check-input" id="validationFormCheck3" name="radio-stacked" required>
    <label class="form-check-label" for="validationFormCheck3">Or toggle this other radio</label>
    <div class="invalid-feedback">More example invalid feedback text</div>
  </div>

  <div class="mb-3">
    <select class="form-select" required aria-label="select example">
      <option value="">Open this select menu</option>
      <option value="1">One</option>
      <option value="2">Two</option>
      <option value="3">Three</option>
    </select>
    <div class="invalid-feedback">Example invalid select feedback</div>
  </div>

  <div class="mb-3">
    <input type="file" class="form-control" aria-label="file example" required>
    <div class="invalid-feedback">Example invalid form file feedback</div>
  </div>

  <div class="mb-3">
    <button class="btn btn-primary" type="submit" disabled>Submit form</button>
  </div>
</form>

工具提示

如果您的表单布局允许，您可以用 .{valid|invalid}-feedback 类 替换 .{valid|invalid}-tooltip类，用于在样式化工具提示中显示验证反馈。确保有一个带有position: relative的父项，以便进行工具提示定位。在下面的示例中，我们的列类已经有此功能，但您的项目可能需要替换设置。

Looks good!
Looks good!
@
Please choose a unique and valid username.
Please provide a valid city.
Please select a valid state.
Please provide a valid zip.
html 
<form class="row g-3 needs-validation" novalidate>
  <div class="col-md-4 position-relative">
    <label for="validationTooltip01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationTooltip01" value="Mark" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-md-4 position-relative">
    <label for="validationTooltip02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationTooltip02" value="Otto" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-md-4 position-relative">
    <label for="validationTooltipUsername" class="form-label">Username</label>
    <div class="input-group has-validation">
      <span class="input-group-text" id="validationTooltipUsernamePrepend">@</span>
      <input type="text" class="form-control" id="validationTooltipUsername" aria-describedby="validationTooltipUsernamePrepend" required>
      <div class="invalid-tooltip">
        Please choose a unique and valid username.
      </div>
    </div>
  </div>
  <div class="col-md-6 position-relative">
    <label for="validationTooltip03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationTooltip03" required>
    <div class="invalid-tooltip">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3 position-relative">
    <label for="validationTooltip04" class="form-label">State</label>
    <select class="form-select" id="validationTooltip04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div class="invalid-tooltip">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3 position-relative">
    <label for="validationTooltip05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationTooltip05" required>
    <div class="invalid-tooltip">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

CSS

变量

Added in v5.3.0

作为 Bootstrap 不断发展的 CSS 变量方法的一部分，表单现在使用本地 CSS 变量进行验证，以增强实时自定义。CSS 变量的值是通过 Sass 设置的，因此仍然支持 Sass 自定义。

scss/_root.scss 
--#{$prefix}form-valid-color: #{$form-valid-color};
--#{$prefix}form-valid-border-color: #{$form-valid-border-color};
--#{$prefix}form-invalid-color: #{$form-invalid-color};
--#{$prefix}form-invalid-border-color: #{$form-invalid-border-color};

这些变量也是颜色模式自适应的，这意味着它们在深色模式下会改变颜色。

Sass variables

scss/_variables.scss 
$form-feedback-margin-top:          $form-text-margin-top;
$form-feedback-font-size:           $form-text-font-size;
$form-feedback-font-style:          $form-text-font-style;
$form-feedback-valid-color:         $success;
$form-feedback-invalid-color:       $danger;

$form-feedback-icon-valid-color:    $form-feedback-valid-color;
$form-feedback-icon-valid:          url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 8 8'><path fill='#{$form-feedback-icon-valid-color}' d='M2.3 6.73.6 4.53c-.4-1.04.46-1.4 1.1-.8l1.1 1.4 3.4-3.8c.6-.63 1.6-.27 1.2.7l-4 4.6c-.43.5-.8.4-1.1.1z'/></svg>");
$form-feedback-icon-invalid-color:  $form-feedback-invalid-color;
$form-feedback-icon-invalid:        url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 12 12' width='12' height='12' fill='none' stroke='#{$form-feedback-icon-invalid-color}'><circle cx='6' cy='6' r='4.5'/><path stroke-linejoin='round' d='M5.8 3.6h.4L6 6.5z'/><circle cx='6' cy='8.2' r='.6' fill='#{$form-feedback-icon-invalid-color}' stroke='none'/></svg>");
scss/_variables.scss 
$form-valid-color:                  $form-feedback-valid-color;
$form-valid-border-color:           $form-feedback-valid-color;
$form-invalid-color:                $form-feedback-invalid-color;
$form-invalid-border-color:         $form-feedback-invalid-color;
scss/_variables-dark.scss 
$form-valid-color-dark:             $green-300;
$form-valid-border-color-dark:      $green-300;
$form-invalid-color-dark:           $red-300;
$form-invalid-border-color-dark:    $red-300;

Sass 混合（Sass mixins）

通过我们的 loop, 将两个 mixin 组合在一起，以生成我们的表单验证反馈样式。

scss/mixins/_forms.scss 
@mixin form-validation-state-selector($state) {
  @if ($state == "valid" or $state == "invalid") {
    .was-validated #{if(&, "&", "")}:#{$state},
    #{if(&, "&", "")}.is-#{$state} {
      @content;
    }
  } @else {
    #{if(&, "&", "")}.is-#{$state} {
      @content;
    }
  }
}

@mixin form-validation-state(
  $state,
  $color,
  $icon,
  $tooltip-color: color-contrast($color),
  $tooltip-bg-color: rgba($color, $form-feedback-tooltip-opacity),
  $focus-box-shadow: 0 0 $input-btn-focus-blur $input-focus-width rgba($color, $input-btn-focus-color-opacity),
  $border-color: $color
) {
  .#{$state}-feedback {
    display: none;
    width: 100%;
    margin-top: $form-feedback-margin-top;
    @include font-size($form-feedback-font-size);
    font-style: $form-feedback-font-style;
    color: $color;
  }

  .#{$state}-tooltip {
    position: absolute;
    top: 100%;
    z-index: 5;
    display: none;
    max-width: 100%; // Contain to parent when possible
    padding: $form-feedback-tooltip-padding-y $form-feedback-tooltip-padding-x;
    margin-top: .1rem;
    @include font-size($form-feedback-tooltip-font-size);
    line-height: $form-feedback-tooltip-line-height;
    color: $tooltip-color;
    background-color: $tooltip-bg-color;
    @include border-radius($form-feedback-tooltip-border-radius);
  }

  @include form-validation-state-selector($state) {
    ~ .#{$state}-feedback,
    ~ .#{$state}-tooltip {
      display: block;
    }
  }

  .form-control {
    @include form-validation-state-selector($state) {
      border-color: $border-color;

      @if $enable-validation-icons {
        padding-right: $input-height-inner;
        background-image: escape-svg($icon);
        background-repeat: no-repeat;
        background-position: right $input-height-inner-quarter center;
        background-size: $input-height-inner-half $input-height-inner-half;
      }

      &:focus {
        border-color: $border-color;
        box-shadow: $focus-box-shadow;
      }
    }
  }

  // stylelint-disable-next-line selector-no-qualifying-type
  textarea.form-control {
    @include form-validation-state-selector($state) {
      @if $enable-validation-icons {
        padding-right: $input-height-inner;
        background-position: top $input-height-inner-quarter right $input-height-inner-quarter;
      }
    }
  }

  .form-select {
    @include form-validation-state-selector($state) {
      border-color: $border-color;

      @if $enable-validation-icons {
        &:not([multiple]):not([size]),
        &:not([multiple])[size="1"] {
          --#{$prefix}form-select-bg-icon: #{escape-svg($icon)};
          padding-right: $form-select-feedback-icon-padding-end;
          background-position: $form-select-bg-position, $form-select-feedback-icon-position;
          background-size: $form-select-bg-size, $form-select-feedback-icon-size;
        }
      }

      &:focus {
        border-color: $border-color;
        box-shadow: $focus-box-shadow;
      }
    }
  }

  .form-control-color {
    @include form-validation-state-selector($state) {
      @if $enable-validation-icons {
        width: add($form-color-width, $input-height-inner);
      }
    }
  }

  .form-check-input {
    @include form-validation-state-selector($state) {
      border-color: $border-color;

      &:checked {
        background-color: $color;
      }

      &:focus {
        box-shadow: $focus-box-shadow;
      }

      ~ .form-check-label {
        color: $color;
      }
    }
  }
  .form-check-inline .form-check-input {
    ~ .#{$state}-feedback {
      margin-left: .5em;
    }
  }

  .input-group {
    > .form-control:not(:focus),
    > .form-select:not(:focus),
    > .form-floating:not(:focus-within) {
      @include form-validation-state-selector($state) {
        @if $state == "valid" {
          z-index: 3;
        } @else if $state == "invalid" {
          z-index: 4;
        }
      }
    }
  }
}

Sass 映射（Sass map）

这是来自_variables.scss的验证 Sass 映射。重写或扩展此设置以生成不同的或其他状态。

scss/_variables.scss 
$form-validation-states: (
  "valid": (
    "color": var(--#{$prefix}form-valid-color),
    "icon": $form-feedback-icon-valid,
    "tooltip-color": #fff,
    "tooltip-bg-color": var(--#{$prefix}success),
    "focus-box-shadow": 0 0 $input-btn-focus-blur $input-focus-width rgba(var(--#{$prefix}success-rgb), $input-btn-focus-color-opacity),
    "border-color": var(--#{$prefix}form-valid-border-color),
  ),
  "invalid": (
    "color": var(--#{$prefix}form-invalid-color),
    "icon": $form-feedback-icon-invalid,
    "tooltip-color": #fff,
    "tooltip-bg-color": var(--#{$prefix}danger),
    "focus-box-shadow": 0 0 $input-btn-focus-blur $input-focus-width rgba(var(--#{$prefix}danger-rgb), $input-btn-focus-color-opacity),
    "border-color": var(--#{$prefix}form-invalid-border-color),
  )
);

$form-validation-states的映射可以包含三个可选参数，用于覆盖工具提示和焦点样式。

Sass 循环（Sass loop）

用于迭代$form-validation-states映射值以生成验证样式。对上述 Sass 映射的任何修改都将通过此循环反映在您编译的 CSS 中。

scss/forms/_validation.scss 
@each $state, $data in $form-validation-states {
  @include form-validation-state($state, $data...);
}

自定义

验证状态可以通过 Sass 使用 $form-validation-states映射进行自定义。位于我们的_variables.scss文件中，这个 Sass 映射是我们生成默认 valid/invalid验证状态的方式。包括一个嵌套映射，用于自定义每个状态的颜色、图标、工具提示颜色和焦点阴影。虽然浏览器不支持其他状态，但使用自定义样式的用户可以轻松添加更复杂的表单反馈。