在CSS中，我們可以使用position屬性來實(shí)現(xiàn)拖拽功能，同時(shí)可以通過設(shè)置initial-value屬性來添加默認(rèn)值，下面是一個(gè)簡單的示例，展示如何在CSS中實(shí)現(xiàn)拖拽框并添加默認(rèn)值：
<!DOCTYPE html>
<html>
<head>
<style>
#draggable {
position: absolute;
width: 100px;
height: 100px;
background-color: #f00;
initial-value: 50; /* 添加默認(rèn)值 */
}
</style>
</head>
<body>
<div id="draggable"></div>
<script>
var draggable = document.getElementById('draggable');
var initialValue = draggable.initialValue; /* 獲取默認(rèn)值 */
var position = 0;
var step = 5; /* 每次移動(dòng)的距離 */
var maxPosition = 500; /* ***大位置 */
var minPosition = 0; /* ***小位置 */
var isDragging = false;
var timer;
var startX;
var startY;
var currentX;
var currentY;
var direction;
var distance;
var newPosition;
var oldPosition;
var element;
var event;
var initialMouseX;
var initialMouseY;
var initialElementX;
var initialElementY;
var dragHandler = function(event) {
event.preventDefault();
if (!isDragging) {
isDragging = true;
startX = event.clientX - initialMouseX;
startY = event.clientY - initialMouseY;
initialElementX = draggable.getBoundingClientRect().left;
initialElementY = draggable.getBoundingClientRect().top;
return;
} else {
currentX = event.clientX - startX;
currentY = event.clientY - startY;
newPosition = initialPosition + currentX * step;
oldPosition = initialPosition - currentX * step;
if (newPosition > maxPosition) { newPosition = maxPosition; } /* 防止超出***大位置 */
if (newPosition < minPosition) { newPosition = minPosition; } /* 防止超出***小位置 */
draggable.style.left = newPosition + 'px'; /* 更新位置 */
}
};
var upHandler = function() {
isDragging = false;
clearTimeout(timer); /* 清除定時(shí)器 */
initialMouseX = event.clientX - currentX; /* 更新初始鼠標(biāo)位置 */
initialMouseY = event.clientY - currentY; /* 更新初始鼠標(biāo)位置 */
initialPosition = newPosition; /* 更新初始位置 */
return false; /* 防止默認(rèn)行為 */
};
draggable.addEventListener('mousedown', function(event) { event.preventDefault(); initialMouseX = event.clientX; initialMouseY = event.clientY; initialPosition = draggable.getBoundingClientRect().left; timer = setTimeout(dragHandler, 0); }, false);
document.addEventListener('mousemove', dragHandler, false);
document.addEventListener('mouseup', upHandler, false);
</script>
</body>
</html>在這個(gè)示例中，我們創(chuàng)建了一個(gè)可拖拽的div元素，并設(shè)置了初始值為50，我們通過JavaScript實(shí)現(xiàn)了拖拽功能，并在拖拽過程中更新了元素的位置，我們還添加了一些防止拖拽超出范圍的代碼，以確保元素始終在允許的范圍內(nèi)移動(dòng)。
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