Question

我目前正在制作一个拖放式JavaScript引擎。我目前正在制作一个“边界”功能，因此drag-object受到具有类.bound的容器的限制。当我创建拖动对象时，我也会发现它是否有界限：

function makeObj(e) {
    obj = new Object();
    obj.element = e;

    obj.boundX = e.parentNode.offsetWidth - e.offsetWidth;
    obj.boundY = e.parentNode.offsetHeight - e.offsetHeight;

    obj.posX = event.clientX - e.offsetLeft;
    obj.posY = event.clientY - e.offsetTop;

    var curleft = curtop = 0;
    if (e.offsetParent) {
        do {
            curleft += e.offsetLeft;
            curtop += e.offsetTop;
            //alert(e.id + ":" + e.innerHTML);
            if(~e.className.search(/bound/)) {
                obj.boundX = curleft - obj.element.offsetLeft;
                obj.boundY = curtop - obj.element.offsetTop;
                return obj;
            }

        } while (e = e.offsetParent);
    }

    return obj;
}

我的循环有效，但设置界限不会。

我希望这个html能影响这个功能：

<div id="center" class="bound">
    <h1>Hello World! <hr /></h1>
    <div id="box" class="bound">
        <p class="drag square" id="one"> One </p>
        <p class="drag square" id="two"> Two </p>
    </div>
</div>

和这个html一样多：

<div id="center"> <!-- Difference is here -->
    <h1>Hello World! <hr /></h1>
    <div id="box" class="bound">
        <p class="drag square" id="one"> One </p>
        <p class="drag square" id="two"> Two </p>
    </div>
</div>

区别在于.bound类，其中position: relative已设置。

这是CSS：

@charset "utf-8";
/* CSS Document */


* {
    padding: 0px;
    margin: 0px;
}    

.drag {
    position: absolute;
    -webkit-user-select: none;
    -moz-user-select: none;
    user-select: none;
}

.bound {
    position: relative;
}

.square {
    width: 100px;
    height: 100px;
    background: red;
    cursor:move;
}

#center {
    width: 500px;
    height: 300px;
    margin: auto;
    margin-top: 50px;
    background-color:#ccc;
    text-align: center;
    border-radius: 25px;
    -moz-border-radius: 25px;
}

#box {
    background-color: #FF3;
    height: 278px;
    border-radius: 0 0 25px 25px;
    -moz-border-radius: 0 0 25px 25px;
    opacity: 0.5;
}

如何使position:属性不影响引擎的工作方式 - 这样任何位置都能正常工作。绝对，相对，静态等？如何使我的.drag对象具有除绝对之外的任何位置？

我会发布下面的整个引擎（以及一个jsfiddle链接）以防它有用：

http://jsfiddle.net/Upvdm/1/

// JavaScript Document

var dragObj;

document.addEventListener("mousedown", down, false);

function down(event) {
    if(~event.target.className.search(/drag/)) {
        dragObj = makeObj(event.target);
        dragObj.element.style.zIndex="100";
        document.addEventListener("mousemove", freeMovement, false);
    }
}

function freeMovement(event) {

    if (typeof(dragObj.element.mouseup) == "undefined")
        document.addEventListener("mouseup", drop, false);
    //Prevents redundantly adding the same event handler repeatedly

dragObj.element.style.left = Math.max(0, Math.min(event.clientX - dragObj.posX, dragObj.boundX)) + "px";
    dragObj.element.style.top = Math.max(0, Math.min(event.clientY - dragObj.posY, dragObj.boundY)) + "px";
}

function drop() {
    dragObj.element.style.zIndex="1";

    document.removeEventListener("mousemove", freeMovement, false);
    document.removeEventListener("mouseup", drop, false);
    //alert("DEBUG_DROP");
}

function makeBoundlessObj(e) {
    obj = new Object();
    obj.element = e;

    obj.boundX = e.parentNode.offsetWidth - e.offsetWidth;
    obj.boundY = e.parentNode.offsetHeight - e.offsetHeight;

    obj.posX = event.clientX - e.offsetLeft;
    obj.posY = event.clientY - e.offsetTop;

    return obj;
}

function makeObj(e) {
    obj = new Object();
    obj.element = e;

    obj.boundX = e.parentNode.offsetWidth - e.offsetWidth;
    obj.boundY = e.parentNode.offsetHeight - e.offsetHeight;

    obj.posX = event.clientX - e.offsetLeft;
    obj.posY = event.clientY - e.offsetTop;

    var curleft = curtop = 0;
    if (e.offsetParent) {
        do {
            curleft += e.offsetLeft;
            curtop += e.offsetTop;
            //alert(e.id + ":" + e.innerHTML);
            if(~e.className.search(/bound/)) {
                obj.boundX = curleft - obj.element.offsetLeft;
                obj.boundY = curtop - obj.element.offsetTop;
                return obj;
            }

        } while (e = e.offsetParent);
    }

    return obj;
}

function findPos(obj) { // Donated by `lwburk` on StackOverflow
    var curleft = curtop = 0;
    if (obj.offsetParent) {
        do {
            curleft += obj.offsetLeft;
            curtop += obj.offsetTop;
        } while (obj = obj.offsetParent);
        return { x: curleft, y: curtop };
    }
}

非常感谢您的阅读和帮助！

Answer 1

while (e = e.offsetParent);

应该是

while (e == e.offsetParent); //alternatively, use ===

在类C语言（如JavaScript）中，=表示“将变量的值放在左侧变量的右侧”。但是，==表示“双方的价值是否匹配？”

JavaScript只考虑一些事情（如0，空字符串，null和undefined）为false，其他所有内容为true。因此，表达式e = e.offsetParent将始终返回true。测试它，它适用于您发送的JSFiddle示例。

定位的类型确实影响了我的JavaScript

1 个答案: