多選與單選（Checks & radios）
使用我們重構過的勾選組件，建立跨瀏覽器、跨設備皆一致的復選框（checkbox）及單選按鈕（radio）。
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方法
瀏覽器默認的復選框和單選按鈕被.form-check所取代，這是一系列用于兩種輸入類型的類，它們改進了HTML元素的布局和行為，提供了更好的自定義和跨瀏覽器一致性。復選框用于在列表中選擇一個或多個選項，而單選按鈕用于從多個選項中選擇一個選項。
在結構上，我們的input和label是兄弟元素，而不是label中的input。由于必須指定id和屬性才能將input和label關聯起來，因此這會稍微詳細一些。我們對所有input狀態使用同級選擇器（~），例如：checked或：disabled。當與.form-check-label類結合使用時，我們可以根據input的狀態輕松地為每個項設置文本樣式。
復選框
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="flexCheckDefault">
<label class="form-check-label" for="flexCheckDefault">
Default checkbox
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="flexCheckChecked" checked>
<label class="form-check-label" for="flexCheckChecked">
Checked checkbox
</label>
</div>不確定
當通過JavaScript手動設置時，復選框可以利用不確定偽類 :indeterminate（沒有可用的HTML屬性來指定它）。
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="flexCheckIndeterminate">
<label class="form-check-label" for="flexCheckIndeterminate">
Indeterminate checkbox
</label>
</div>禁用
添加disabled屬性，相關的label將自動設置為與較淺顏色匹配的樣式，以幫助指示輸入的狀態。
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="flexCheckDisabled" disabled>
<label class="form-check-label" for="flexCheckDisabled">
Disabled checkbox
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="flexCheckCheckedDisabled" checked disabled>
<label class="form-check-label" for="flexCheckCheckedDisabled">
Disabled checked checkbox
</label>
</div>單選按鈕
<div class="form-check">
<input class="form-check-input" type="radio" name="flexRadioDefault" id="flexRadioDefault1">
<label class="form-check-label" for="flexRadioDefault1">
Default radio
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" name="flexRadioDefault" id="flexRadioDefault2" checked>
<label class="form-check-label" for="flexRadioDefault2">
Default checked radio
</label>
</div>禁用
添加disabled屬性，相關的label將自動設置為與較淺顏色匹配的樣式，以幫助指示輸入的狀態。
<div class="form-check">
<input class="form-check-input" type="radio" name="flexRadioDisabled" id="flexRadioDisabled" disabled>
<label class="form-check-label" for="flexRadioDisabled">
Disabled radio
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" name="flexRadioDisabled" id="flexRadioCheckedDisabled" checked disabled>
<label class="form-check-label" for="flexRadioCheckedDisabled">
Disabled checked radio
</label>
</div>開關
開關具有自定義復選框的標記，但使用.form-switch類來呈現切換開關。開關還支持disabled屬性。
<div class="form-check form-switch">
<input class="form-check-input" type="checkbox" id="flexSwitchCheckDefault">
<label class="form-check-label" for="flexSwitchCheckDefault">Default switch checkbox input</label>
</div>
<div class="form-check form-switch">
<input class="form-check-input" type="checkbox" id="flexSwitchCheckChecked" checked>
<label class="form-check-label" for="flexSwitchCheckChecked">Checked switch checkbox input</label>
</div>
<div class="form-check form-switch">
<input class="form-check-input" type="checkbox" id="flexSwitchCheckDisabled" disabled>
<label class="form-check-label" for="flexSwitchCheckDisabled">Disabled switch checkbox input</label>
</div>
<div class="form-check form-switch">
<input class="form-check-input" type="checkbox" id="flexSwitchCheckCheckedDisabled" checked disabled>
<label class="form-check-label" for="flexSwitchCheckCheckedDisabled">Disabled checked switch checkbox input</label>
</div>默認 (疊放)
默認情況下，任何數量的直接同級復選框和單選按鈕都將垂直堆疊，并使用 .form-check適當隔開。
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="defaultCheck1">
<label class="form-check-label" for="defaultCheck1">
Default checkbox
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="checkbox" value="" id="defaultCheck2" disabled>
<label class="form-check-label" for="defaultCheck2">
Disabled checkbox
</label>
</div><div class="form-check">
<input class="form-check-input" type="radio" name="exampleRadios" id="exampleRadios1" value="option1" checked>
<label class="form-check-label" for="exampleRadios1">
Default radio
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" name="exampleRadios" id="exampleRadios2" value="option2">
<label class="form-check-label" for="exampleRadios2">
Second default radio
</label>
</div>
<div class="form-check">
<input class="form-check-input" type="radio" name="exampleRadios" id="exampleRadios3" value="option3" disabled>
<label class="form-check-label" for="exampleRadios3">
Disabled radio
</label>
</div>內聯
通過將.form-check-inline添加到.form-check，將復選框或單選框在同一水平行上分組顯示。
<div class="form-check form-check-inline">
<input class="form-check-input" type="checkbox" id="inlineCheckbox1" value="option1">
<label class="form-check-label" for="inlineCheckbox1">1</label>
</div>
<div class="form-check form-check-inline">
<input class="form-check-input" type="checkbox" id="inlineCheckbox2" value="option2">
<label class="form-check-label" for="inlineCheckbox2">2</label>
</div>
<div class="form-check form-check-inline">
<input class="form-check-input" type="checkbox" id="inlineCheckbox3" value="option3" disabled>
<label class="form-check-label" for="inlineCheckbox3">3 (disabled)</label>
</div><div class="form-check form-check-inline">
<input class="form-check-input" type="radio" name="inlineRadioOptions" id="inlineRadio1" value="option1">
<label class="form-check-label" for="inlineRadio1">1</label>
</div>
<div class="form-check form-check-inline">
<input class="form-check-input" type="radio" name="inlineRadioOptions" id="inlineRadio2" value="option2">
<label class="form-check-label" for="inlineRadio2">2</label>
</div>
<div class="form-check form-check-inline">
<input class="form-check-input" type="radio" name="inlineRadioOptions" id="inlineRadio3" value="option3" disabled>
<label class="form-check-label" for="inlineRadio3">3 (disabled)</label>
</div>無標簽
對于沒有標簽文本的復選框和收音機，省略wrapping.form復選框。記住，仍然要為輔助技術提供某種形式的可訪問名稱（例如，使用aria-label標簽）。有關詳細信息，請參見表單概述輔助功能部分。
<div>
<input class="form-check-input" type="checkbox" id="checkboxNoLabel" value="" aria-label="...">
</div>
<div>
<input class="form-check-input" type="radio" name="radioNoLabel" id="radioNoLabel1" value="" aria-label="...">
</div>切換按鈕
通過使用.btn樣式而不是
復選切換按鈕
<input type="checkbox" class="btn-check" id="btn-check" autocomplete="off">
<label class="btn btn-primary" for="btn-check">Single toggle</label><input type="checkbox" class="btn-check" id="btn-check-2" checked autocomplete="off">
<label class="btn btn-primary" for="btn-check-2">Checked</label><input type="checkbox" class="btn-check" id="btn-check-3" autocomplete="off" disabled>
<label class="btn btn-primary" for="btn-check-3">Disabled</label>
從外觀上看，這些復選框切換按鈕與按鈕插件切換按鈕相同。然而，輔助技術傳達的方式不同：屏幕閱讀器會將復選框切換宣布為“選中”/“未選中”（因為外觀如此，但它們本質上仍然是復選框），而按鈕插件切換按鈕將宣布為“按鈕”/“按下按鈕”。這兩種方法之間的選擇將取決于您正在創建的切換類型，以及當作為復選框或實際按鈕發布時，切換對用戶是否有意義。
單選切換按鈕
<input type="radio" class="btn-check" name="options" id="option1" autocomplete="off" checked>
<label class="btn btn-secondary" for="option1">Checked</label>
<input type="radio" class="btn-check" name="options" id="option2" autocomplete="off">
<label class="btn btn-secondary" for="option2">Radio</label>
<input type="radio" class="btn-check" name="options" id="option3" autocomplete="off" disabled>
<label class="btn btn-secondary" for="option3">Disabled</label>
<input type="radio" class="btn-check" name="options" id="option4" autocomplete="off">
<label class="btn btn-secondary" for="option4">Radio</label>輪廓樣式
支持.btn的不同變量，例如各種outline樣式是被支持的。
<input type="checkbox" class="btn-check" id="btn-check-outlined" autocomplete="off">
<label class="btn btn-outline-primary" for="btn-check-outlined">Single toggle</label><br>
<input type="checkbox" class="btn-check" id="btn-check-2-outlined" checked autocomplete="off">
<label class="btn btn-outline-secondary" for="btn-check-2-outlined">Checked</label><br>
<input type="radio" class="btn-check" name="options-outlined" id="success-outlined" autocomplete="off" checked>
<label class="btn btn-outline-success" for="success-outlined">Checked success radio</label>
<input type="radio" class="btn-check" name="options-outlined" id="danger-outlined" autocomplete="off">
<label class="btn btn-outline-danger" for="danger-outlined">Danger radio</label>Sass
Variables
$form-check-input-width: 1em;
$form-check-min-height: $font-size-base * $line-height-base;
$form-check-padding-start: $form-check-input-width + .5em;
$form-check-margin-bottom: .125rem;
$form-check-label-color: null;
$form-check-label-cursor: null;
$form-check-transition: null;
$form-check-input-active-filter: brightness(90%);
$form-check-input-bg: $input-bg;
$form-check-input-border: 1px solid rgba(0, 0, 0, .25);
$form-check-input-border-radius: .25em;
$form-check-radio-border-radius: 50%;
$form-check-input-focus-border: $input-focus-border-color;
$form-check-input-focus-box-shadow: $input-btn-focus-box-shadow;
$form-check-input-checked-color: $component-active-color;
$form-check-input-checked-bg-color: $component-active-bg;
$form-check-input-checked-border-color: $form-check-input-checked-bg-color;
$form-check-input-checked-bg-image: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20'><path fill='none' stroke='#{$form-check-input-checked-color}' stroke-linecap='round' stroke-linejoin='round' stroke-width='3' d='M6 10l3 3l6-6'/></svg>");
$form-check-radio-checked-bg-image: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='-4 -4 8 8'><circle r='2' fill='#{$form-check-input-checked-color}'/></svg>");
$form-check-input-indeterminate-color: $component-active-color;
$form-check-input-indeterminate-bg-color: $component-active-bg;
$form-check-input-indeterminate-border-color: $form-check-input-indeterminate-bg-color;
$form-check-input-indeterminate-bg-image: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 20 20'><path fill='none' stroke='#{$form-check-input-indeterminate-color}' stroke-linecap='round' stroke-linejoin='round' stroke-width='3' d='M6 10h8'/></svg>");
$form-check-input-disabled-opacity: .5;
$form-check-label-disabled-opacity: $form-check-input-disabled-opacity;
$form-check-btn-check-disabled-opacity: $btn-disabled-opacity;
$form-check-inline-margin-end: 1rem;