我试图在 javascript、html 和 css 中创建一个下拉菜单，但是当我运行代码时， Canvas 上没有显示任何内容。是因为文件之间没有正确通信吗？
HTML:
<!DOCTYPE html>
<html>
<head>
<title>DropdownMenu</title>
<link rel='stylesheet' type='text/css' href='Stylesheetdropdown.css'/>
</head>
<body>
<canvas id="canvas" width="5000" height="5000">
</canvas>
<script type='text/javascript' src='DropdownMenu.js'></script>
</body>
<body>
<div class = "dropdown">
<button onclick = "dropdown()" class = "drpdwnbtn">Menu</button>
<div id = "myMenu" class = "drpdwncntnt">
<p>100</p>
<p>200</p>
<p>300</p>
</div>
</div>
</body>
</html>
Javascript:
function dropdown() {
document.getElementById("myMenu").classList.toggle("show");
}
window.onclick = function (event) {
if (!event.target.matches('.drpdwnbtn')) {
var dropdowns = document.getElementsByClassName("drpdwncntnt"),
i,
openDropdown = dropdowns[i];
for (i = 0; i < dropdowns.length; i += 1) {
if (openDropdown.classList.contains('show')) {
openDropdown.classList.remove('show');
}
}
}
};
CSS:
.drpdwnbtn {
background-color: #4CAF50;
color: white;
padding: 16px;
font-size: 16px;
border: none;
cursor: pointer;
}
.drpdwnbtn:hover, .drpdwnbtn:focus {
background-color: #E0FFFF;
}
.dropdown {
position: relative;
display: inline-block;
}
.drpdwncntnt {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 160px;
overflow: auto;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
}
.drpdwncntnt a {
color: black;
padding: 12px 16px;
text-decoration: none;
display: block;
}
.dropdown a:hover {background-color: #f1f1f1}
.show {display:block;}
最佳答案
您的 Canvas 位于菜单 div 上方，您的 html 应如下所示:
<div class = "dropdown">
<button onclick = "dropdown()" class = "drpdwnbtn">Menu</button>
<div id = "myMenu" class = "drpdwncntnt">
<p>100</p>
<p>200</p>
<p>300</p>
</div>
</div>
<canvas id="canvas" width="5000" height="5000">
</canvas>
，所以这是一个有效的 fiddle :
关于javascript - 在 Javascript 中创建下拉菜单 - Canvas 上没有显示，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45214232/