检查是否加载了多个图像
我正在使用html5的canvas功能。我有一些图像要在画布上绘制,我需要检查它们是否已全部加载,然后才能使用它们。
我已在数组中声明它们,我需要一种方法来检查它们是否已同时加载,但我不知道如何执行此操作。
这是我的代码:
var color = new Array();
color[0] = new Image();
color[0].src = "green.png";
color[1] = new Image();
color[1].src = "blue.png";
目前要检查图像是否已加载,我必须像这样一张一张地执行:
color[0].onload = function(){
//code here
}
color[1].onload = function(){
//code here
}
如果我有更多图像,我稍后将在开发中,这将是一种非常低效的方法检查他们全部。
我如何同时检查它们?
I'm using the canvas feature of html5. I've got some images to draw on the canvas and I need to check that they have all loaded before I can use them.
I have declared them inside an array, I need a way of checking if they have all loaded at the same time but I am not sure how to do this.
Here is my code:
var color = new Array();
color[0] = new Image();
color[0].src = "green.png";
color[1] = new Image();
color[1].src = "blue.png";
Currently to check if the images have loaded, I would have to do it one by one like so:
color[0].onload = function(){
//code here
}
color[1].onload = function(){
//code here
}
If I had a lot more images, Which I will later in in development, This would be a really inefficient way of checking them all.
How would I check them all at the same time?
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如果您想在加载所有图像时调用一个函数,您可以尝试以下操作,它对我有用
If you want to call a function when all the images are loaded, You can try following, it worked for me
难道不能简单地使用循环并将相同的函数分配给所有加载吗?
Can't you simply use a loop and assign the same function to all onloads?
使用当所有图像和外部资源加载时触发的
window.onload
:因此,您可以安全地放置与图像相关的代码在
window.onload
中,因为此时所有图像都已加载。更多信息请点击此处。
Use the
window.onload
which fires when all images/frames and external resources are loaded:So, you can safely put your image-related code in
window.onload
because by the time all images have already loaded.More information here.
使用
Promise
的解决方案是:The solution with
Promise
would be:一种 hackish 方法是将 JS 命令添加到另一个文件中并将其放在页脚中。这样它会最后加载。
然而,使用 jQuery(document).ready 也比原生 window.onload 效果更好。
您正在使用 Chrome,不是吗?
A hackish way to do it is add the JS command in another file and place it in the footer. This way it loads last.
However, using jQuery(document).ready also works better than the native window.onload.
You are using Chrome aren't you?
仅
for 循环
中的onload
方法无法解决此任务,因为onload
方法在循环中异步执行。因此,如果您仅对循环中的最后一个图像进行某种回调,则可能会跳过循环中间的较大图像。您可以使用 Async Await 链接循环以同步跟踪图像加载。
但这种方法的缺点是它增加了加载时间,因为所有图像都是同步加载的。
您还可以使用简单的
for 循环
并在每次迭代后运行回调来更新/处理最新加载的图像值。这样您就不必等待只有在最大图像之后才加载较小图像的情况。或者只是使用这种方法在所有图像加载后进行回调。
这完全取决于您想做什么。希望它会对某人有所帮助。
Just
onload
method infor loop
does not solve this task, sinceonload
method is executing asynchronously in the loop. So that larger images in the middle of a loop may be skipped in case if you have some sort of callback just for the last image in the loop.You can use Async Await to chain the loop to track image loading synchronously.
But the disadvantage of this method that it increases loading time since all images are loading synchronously.
Also you can use simple
for loop
and run callback after each iteration to update/process latest loaded image value. So that you do not have to wait when smaller images are loaded only after the largest.Or just use this approach to make a callback after all images are loaded.
It all depends on what you want to do. Hope it will help to somebody.
试试这个代码:
try this code: