AngularJs Protractor：滑出菜单中的元素不可见

我带着更多量角器问答回来了。因此，我在尝试查找滑出菜单内的元素时遇到了一个问题。

html 片段：

<div class="ng-scope" ui-view="navmenu">
<nav class="menu slide-menu-left ng-scope">
  <md-content class="md-default-theme" style="display: table" ng-click="slideMenuLeft()" tabindex="0">
    <button class="md-button md-default-theme" ng-transclude="" 
            style="width:50%;height:72px;border-right:1px solid #ddd;border-bottom:1px solid #ddd" 
            ng-click="checkmap()" tabindex="0">

以下是我尝试从此菜单中获取按钮的方法：

element(by.css('Button[ng-click="logoff()"]'));
element(by.xpath('/html/body/section/div[@class="ng-scope"]/nav[@class="menu slide-menu-left ng-scope"]/md-content/button[@ng-click="logoff()"]'));

量角器不喜欢并继续告诉我这一点：

Stacktrace:
  ElementNotVisibleError: element not visible
  (Session info: chrome=40.0.2214.115)
  (Driver info: chromedriver=2.14.313457 (3d645c400edf2e2c500566c9aa096063e707c9cf),platform=Windows NT 6.3 x86_64) (WARNING: The server did not provide any stacktrace information)
Command duration or timeout: 31 milliseconds
Build info: version: '2.45.0', revision: '5017cb8', time: '2015-02-26 23:59:50'

谁能就我可能做错的事情提出建议？

您需要先打开菜单，然后才能找到并单击子菜单：

element(by.css('nav.menu > md-content')).click();
element(by.css('nav.menu > md-content > button[ng-click="logoff()"]')).click();

您可能还需要使用elementToBeClickable 预期状况 to 等待子菜单变得可点击（需要量角器1.7或以上）：

var EC = protractor.ExpectedConditions;
var logoff = element(by.css('nav.menu > md-content > button[ng-click="logoff()"]'));

browser.wait(EC.elementToBeClickable(logoff), 10000);
logoff.click();