ngClass未在指令中成功更新

Question

我创建了一个指令，它创建一个带有ul元素的弹出窗口，但是ng-class = isVisible没有返回正确的值。它是有效的，如果我在我的页面上只使用了一个指令，但是当它在多个时，它不起作用。

我的问题是，使用此范围函数时不会更新ngClass。

function _isElementVisible(el, parent) {
var eap,
    rect = el.getBoundingClientRect(),
    docEl = parent,
    vWidth = docEl.clientWidth,
    vHeight = docEl.clientHeight,
    efp = function (x, y) { return document.elementFromPoint(x, y) },
    contains = "contains" in el ? "contains" : "compareDocumentPosition",
    has = contains == "contains" ? 1 : 0x14;

// Return false if it's not in the viewport
if (rect.right < 0 || rect.bottom < 0
    || rect.left > vWidth || rect.top > vHeight)
    return false;

// Return true if any of its four corners are visible
return (
    (eap = efp(rect.left, rect.top)) == el || el[contains](eap) == has
    || (eap = efp(rect.right, rect.top)) == el || el[contains](eap) == has
    || (eap = efp(rect.right, rect.bottom)) == el || el[contains](eap) == has
    || (eap = efp(rect.left, rect.bottom)) == el || el[contains](eap) == has
    );
}

scope.isVisible = function (index) {
if (!scope.active)
    return false;

return _isElementVisible(jqElm.find('.modal li')[index], jqElm.find('.modal')[0]);
}

<li ng-repeat="item in items" ng-class="{'visible': isVisible($index)}"></li>