Bootstrap表单验证

Bootstrap表单验证使用JavaScript和jQuery来实现，并且需要与HTML5表单一起使用。它提供了一些内置的验证规则，例如必填字段、电子邮件格式、文件格式等。此外，它还允许开发人员自定义验证规则以满足特定的需求。

虽然目前客户端的自定义验证样式和工具提示是无障碍的，自从它们不暴露于辅助技术。在处理解决方案时，建议使用服务器端选项或默认浏览器验证方法。

一、工作原理

下面是Bootstrap表单验证的工作原理：

1、HTML表单验证是通过CSS的两个伪类：invalid和：valid应用的。它适用于input、select和textarea元素。

2、Bootstrap 作用域：invalid和：valid样式到父.was-validated类，通常应用于form。否则，任何不带值的必填字段在页面加载时显示为无效。这样，您可以选择何时激活它们（通常在尝试提交表单之后）。

3、要重置表单的外观（例如，在使用AJAX提交动态表单的情况下），请在提交后再次从form中移除.was-validated类。

4、As a fallback, .is-invalid and .is-valid 作为回退，.is-invalid and .is-valid类可以代替伪类用于服务器端验证。它们不需要.was-validated的父类。

5、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）无法将样式应用到DOM中表单控件之前的label。

6、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。

7、反馈消息可以利用 浏览器默认值（每个浏览器的默认值不同，通过CSS不可改变）或我们的自定义反馈样式以及额外的HTML和CSS。

8、可以在JavaScript中使用setCustomValidity提供自定义有效性消息。

接下来请结合以下示例，了解Bootstrap的自定义表单验证样式、可选服务器端类和浏览器默认值。

二、自定义样式

对于自定义Bootstrap表单验证消息，需要将novalidate布尔属性添加到form。这将禁用浏览器默认的反馈工具提示，但仍提供对JavaScript中表单验证api的访问。尝试提交以下表格；我们的JavaScript将截获提交按钮并向您传递反馈。尝试提交时，您将看到：invalid和：valid样式应用于表单控件。

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来更好地传达反馈。select的背景图标仅适用于.form-select，而不适用于.form-control。

<form class="needs-validation" novalidate>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationCustom01">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-6 mb-3">
<label for="validationCustom02">Last name</label>
<input type="text" class="form-control" id="validationCustom02" value="Otto" required>
<div class="valid-feedback">
Looks good!
</div>
</div>
</div>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationCustom03">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 mb-3">
<label for="validationCustom04">State</label>
<select class="custom-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 mb-3">
<label for="validationCustom05">Zip</label>
<input type="text" class="form-control" id="validationCustom05" required>
<div class="invalid-feedback">
Please provide a valid zip.
</div>
</div>
</div>
<div class="form-group">
<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>
<button class="btn btn-primary" type="submit">Submit form</button>
</form>
<script>
// Example starter JavaScript for disabling form submissions if there are invalid fields
(function() {
'use strict';
window.addEventListener('load', function() {
// Fetch all the forms we want to apply custom Bootstrap validation styles to
var forms = document.getElementsByClassName('needs-validation');
// Loop over them and prevent submission
var validation = Array.prototype.filter.call(forms, function(form) {
form.addEventListener('submit', function(event) {
if (form.checkValidity() === false) {
event.preventDefault();
event.stopPropagation();
}
form.classList.add('was-validated');
}, false);
});
}, false);
})();
</script>

三、浏览器默认值

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？很好，你可以使用浏览器的默认值。试着提交下面的表格。根据您的浏览器和操作系统，您将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，但是您仍然可以通过JavaScript自定义反馈文本。

<form>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationDefault01">First name</label>
<input type="text" class="form-control" id="validationDefault01" value="Mark" required>
</div>
<div class="col-md-6 mb-3">
<label for="validationDefault02">Last name</label>
<input type="text" class="form-control" id="validationDefault02" value="Otto" required>
</div>
</div>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationDefault03">City</label>
<input type="text" class="form-control" id="validationDefault03" required>
</div>
<div class="col-md-3 mb-3">
<label for="validationDefault04">State</label>
<select class="custom-select" id="validationDefault04" required>
<option selected disabled value="">Choose...</option>
<option>...</option>
</select>
</div>
<div class="col-md-3 mb-3">
<label for="validationDefault05">Zip</label>
<input type="text" class="form-control" id="validationDefault05" required>
</div>
</div>
<div class="form-group">
<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>
<button class="btn btn-primary" type="submit">Submit form</button>
</form>

四、服务器端

我们建议使用客户端验证，但如果需要服务器端验证，可以用.is-invalid和.is-valid指示无效和有效的表单字段。注意。这些类也支持无效反馈。

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（注意，如果该字段已指向其他表单文本，则此属性允许引用多个id）。

若要解决边界半径的问题，输入组需要额外的.has-validation。

<form>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationServer01">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-6 mb-3">
<label for="validationServer02">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>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationServer03">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 mb-3">
<label for="validationServer04">State</label>
<select class="custom-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 mb-3">
<label for="validationServer05">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>
<div class="form-group">
<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>
<button class="btn btn-primary" type="submit">Submit form</button>
</form>

五、支持的元素

验证样式可用于以下表单控件和组件：

• <input>s 和 s 与<textarea>.form-control
• <select>s 与 或.form-control.custom-select
• .form-checks
• .custom-checkboxs 和 s.custom-radio
• .custom-file

<form class="was-validated">
<div class="mb-3">
<label for="validationTextarea">Textarea</label>
<textarea class="form-control is-invalid" id="validationTextarea" placeholder="Required example textarea" required></textarea>
<div class="invalid-feedback">
Please enter a message in the textarea.
</div>
</div>
<div class="custom-control custom-checkbox mb-3">
<input type="checkbox" class="custom-control-input" id="customControlValidation1" required>
<label class="custom-control-label" for="customControlValidation1">Check this custom checkbox</label>
<div class="invalid-feedback">Example invalid feedback text</div>
</div>
<div class="custom-control custom-radio">
<input type="radio" class="custom-control-input" id="customControlValidation2" name="radio-stacked" required>
<label class="custom-control-label" for="customControlValidation2">Toggle this custom radio</label>
</div>
<div class="custom-control custom-radio mb-3">
<input type="radio" class="custom-control-input" id="customControlValidation3" name="radio-stacked" required>
<label class="custom-control-label" for="customControlValidation3">Or toggle this other custom radio</label>
<div class="invalid-feedback">More example invalid feedback text</div>
</div>
<div class="mb-3">
<select class="custom-select" required>
<option value="">Choose...</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>
<div class="invalid-feedback">Example invalid custom select feedback</div>
</div>
<div class="custom-file mb-3">
<input type="file" class="custom-file-input" id="validatedCustomFile" required>
<label class="custom-file-label" for="validatedCustomFile">Choose file...</label>
<div class="invalid-feedback">Example invalid custom file feedback</div>
</div>
<div class="mb-3">
<div class="input-group is-invalid">
<div class="input-group-prepend">
<span class="input-group-text" id="validatedInputGroupPrepend">@</span>
</div>
<input type="text" class="form-control is-invalid" aria-describedby="validatedInputGroupPrepend" required>
</div>
<div class="invalid-feedback">
Example invalid input group feedback
</div>
</div>
<div class="mb-3">
<div class="input-group is-invalid">
<div class="input-group-prepend">
<label class="input-group-text" for="validatedInputGroupSelect">Options</label>
</div>
<select class="custom-select" id="validatedInputGroupSelect" required>
<option value="">Choose...</option>
<option value="1">One</option>
<option value="2">Two</option>
<option value="3">Three</option>
</select>
</div>
<div class="invalid-feedback">
Example invalid input group feedback
</div>
</div>
<div class="input-group is-invalid">
<div class="custom-file">
<input type="file" class="custom-file-input" id="validatedInputGroupCustomFile" required>
<label class="custom-file-label" for="validatedInputGroupCustomFile">Choose file...</label>
</div>
<div class="input-group-append">
<button class="btn btn-outline-secondary" type="button">Button</button>
</div>
</div>
<div class="invalid-feedback">
Example invalid input group feedback
</div>
</form>

六、工具提示

如果表单布局允许，可以将.{valid|invalid}-feedback类替换为.{valid|invalid}-tooltip类，以在样式化的工具提示中显示验证反馈。确保在工具提示定位时有一个带有position: relative的父级。在下面的示例中，我们的列类已经有了这种设置，但是您的项目可能需要另一种设置。

<form class="needs-validation" novalidate>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationTooltip01">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-6 mb-3">
<label for="validationTooltip02">Last name</label>
<input type="text" class="form-control" id="validationTooltip02" value="Otto" required>
<div class="valid-tooltip">
Looks good!
</div>
</div>
</div>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationTooltip03">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 mb-3">
<label for="validationTooltip04">State</label>
<select class="custom-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 mb-3">
<label for="validationTooltip05">Zip</label>
<input type="text" class="form-control" id="validationTooltip05" required>
<div class="invalid-tooltip">
Please provide a valid zip.
</div>
</div>

七、定制

验证状态可以通过 Sass 和地图进行自定义。位于我们的$form-validation-states_variables.scssvalidinvalid文件中，此 Sass 映射被循环以生成默认/验证状态。包括一个嵌套地图，用于自定义每个州的颜色和图标。虽然浏览器不支持其他状态，但使用自定义样式的浏览器可以轻松添加更复杂的表单反馈。

注意：不建议在不修改 mixin 的情况下自定义form-validation-state。

// Sass map from `_variables.scss`
// Override this and recompile your Sass to generate different states
$form-validation-states: map-merge(
(
"valid": (
"color": $form-feedback-valid-color,
"icon": $form-feedback-icon-valid
),
"invalid": (
"color": $form-feedback-invalid-color,
"icon": $form-feedback-icon-invalid
)
),
$form-validation-states
);
// Loop from `_forms.scss`
// Any modifications to the above Sass map will be reflected in your compiled
// CSS via this loop.
@each $state, $data in $form-validation-states {
@include form-validation-state($state, map-get($data, color), map-get($data, icon));
}

八、输入组验证

若要通过验证检测输入组内哪些元素需要圆角，输入.has-validation组需要一个附加类。

<div class="input-group has-validation">
<div class="input-group-prepend">
<span class="input-group-text">@</span>
</div>
<input type="text" class="form-control" required>
<div class="invalid-feedback">
Please choose a username.
</div>
</div>