我创建了一个简单的小型库来简化图像的加载。
检查演示
请参阅下面的库代码：
// Simple Image Loader Library
window.Loader = (function () {
var imageCount = 0;
var loading = false;
var total = 0;
// this object will hold all image references
var images = {};
// user defined callback, called each time an image is loaded (if it is not defined the empty function wil be called)
function onProgressUpdate() {};
// user defined callback, called when all images are loaded (if it is not defined the empty function wil be called)
function onComplete() {};
function onLoadImage(name) {
++imageCount;
console.log(name + " loaded");
// call the user defined callback when an image is loaded
onProgressUpdate();
// check if all images are loaded
if (imageCount == total) {
loading = false;
console.log("Load complete.");
onComplete();
}
};
function onImageError(e) {
console.log("Error on loading the image: " + e.srcElement);
}
function loadImage(name, src) {
try {
images[name] = new Image();
images[name].onload = function () {
onLoadImage(name);
};
images[name].onerror = onImageError;
images[name].src = src;
} catch (e) {
console.log(e.message);
}
}
function getImage(/**String*/ name){
if(images[name]){
return (images[name]);
}
else{
return undefined;
}
}
// pre-load all the images and call the onComplete callback when all images are loaded
// optionaly set the onProgressUpdate callback to be called each time an image is loaded (useful for loading screens)
function preload( /**Array*/ _images, /**Callback*/ _onComplete, /**Callback <optional>*/ _onProgressUpdate) {
if (!loading) {
console.log("Loading...");
loading = true;
try {
total = _images.length;
onProgressUpdate = _onProgressUpdate || (function(){});
onComplete = _onComplete || (function(){});
for (var i = 0; i < _images.length; ++i) {
loadImage(_images[i].name, _images[i].src);
}
} catch (e) {
console.log(e.message);
}
} else {
throw new Error("Acess denied: Cannot call the load function while there are remaining images to load.");
}
}
// percentage of progress
function getProgress() {
return (imageCount / total)*100;
};
// return only the public stuff to create our Loader object
return {
preload: preload,
getProgress: getProgress,
getImage: getImage,
images: images // have access to the array of images might be useful but is not necessary
};
})();
这个怎么运作
为了确保图像已加载并且您的应用程序可以使用它们，库具有该Loader.preload方法。
preload 方法将接收一个对象数组，每个对象都包含您要加载的图像的名称和 src 属性。或者，您可以设置onComplete回调（在加载所有图像时调用）和onProgressUpdate回调（在每次加载图像时调用）。如果您想为您的onProgressUpdate应用程序创建加载屏幕，则回调很有用。
使用Loader.getProgress()获取随时加载的图像的百分比。
要获取加载的图像的引用，请调用Loader.getImage(name)其中 name 是图像的名称属性（字符串）。
如果您出于某种原因需要遍历所有图像，请使用Loader.images. 它是在其属性中包含对图像的所有引用的对象。
像这样使用：
var images = [{name: "img1", src: "http://...a.."},
{name: "img2", src: "http://...b.."},
...
{name: "imgN", src: "http://...N.."}];
function onProgressUpdate(progress){
...
drawProgressBar(progress); // just an example of what you can do
...
}
function onComplete(){
...
// get an Image from Loader object
var texture = Loader.getImage("img2");
// or use this:
var texture = Loader.images.img2; // or still Loader.images["img2"]
...
// iterate over the images
for (var img in Loader.images){
console.log(Loader.images[img].src);
}
....
}
Loader.preload(images, onComplete, onProgressUpdate);
如果没有，请检查演示。