[英]Updating global variable via callback
我有以下功能
var urls = '';
handleFiles(f,function(url){
urls = urls + url + ',';
console.log("urls is " + urls);
});
上载后我得到了网址并更新了我的网址。 但是我的Urls从未更新过,它显示了上次上传文件的网址。
更新1这是我现在完整的代码。
var urls = '';
document.getElementById('question-file-selector').addEventListener('change',handleFileSelect,false);
function handleFileSelect(evt){
var files = evt.target.files; //File list object
// Loop through file list, render image files as thumbnails
for (var i = 0,f;f = files[i];i++){
handleFiles(f,function(url){
urls = urls + url + ',';
console.log("urls is " + urls);
});
// Only process image files
if (!f.type.match('image.*')){
$('#list').append('<img class="file-thumb" src="/static/download168.png"/>');
continue;
}
var reader = new FileReader();
//Closure to capture file information
reader.onload = (function(theFile){
return function(e){
//Render thumbnail
$('#list').append('<img class="thumb" src="'+e.target.result+'" title="'+escape(theFile.name)+'"/>');
};
})(f);
reader.readAsDataURL(f);
}
}
console.log("Url is",urls);`
还有我的ajax功能
//Code for Image upload
// Custom jQuery xhr instance to support our progress bar.
var xhr_with_progress = function() {
var xhr = new XMLHttpRequest();
xhr.upload.addEventListener("progress",
function(evt) {
if (!evt.lengthComputable) return;
var percentComplete = evt.loaded / evt.total;
$("#progress-bar div.progress-bar").css('width', String(100*percentComplete) + "%");
}, false);
return xhr;
};
$.support.cors = true;//For cross origin transfer
//Event listners to avoid default drag and drop reaction of browser
window.addEventListener("dragover",function(e){
e = e || event;
e.preventDefault();
},false);
window.addEventListener("drop",function(e){
e = e || event;
e.preventDefault();
},false);
function handleFiles(file,callback){
var filename = file.name;
$.ajax({
type:'GET',
data:{"filename":file.name, "FileType":"question_file"},
url:'/dashboard/generateuploadurl/',
contentType:"application/json",
dataType:"json",
async:false,
success: function(data){
if(data.UploadUrl){
console.log("upload url successfully created for " + file.name + " file");
console.log(data.UploadUrl);
handleUpload(data.UploadUrl, file, data.Filename,callback);
}
},
error: function(data){
console.log("error occured while creating upload url for " + file.name + ' file');
console.log(data);
},
});
}
function handleUpload(UploadUrl, file, Filename,callback){
$.ajax({
xhr:xhr_with_progress,
url:UploadUrl,
type:'PUT',
data:file,
cache:false,
contentType:false,
processData:false,
success: function(data){
console.log('https://7c.ssl.cf6.rackcdn.com/'+ Filename);
callback('https://7c.ssl.cf6.rackcdn.com/'+ Filename);
},
error: function(data){
alert("error occured while uploading " + file.name );
console.log(data);
},
});
}
使用诺言之类的工具可以最好地解决多个异步操作的协调工作。 因此,从长远来看,我建议您阅读有关诺言以及如何使用诺言的内容。
没有承诺,这是一种蛮力方式,您可以通过使用计数器来知道何时完成了最后一个异步操作,然后使用urls
变量INSIDE来完成所有handleFiles()
操作的完成时间,该变量最后一次回调或从那里调用函数,将urls
变量传递给该函数:
document.getElementById('question-file-selector').addEventListener('change', handleFileSelect, false);
function handleFileSelect(evt) {
var files = evt.target.files; //File list object
var urls = "";
// Loop through file list, render image files as thumbnails
var doneCnt = 0;
for (var i = 0, f; f = files[i]; i++) {
handleFiles(f, function (url) {
urls = urls + url + ',';
console.log("urls is " + urls);
++doneCnt;
if (doneCnt === files.length) {
// The last handleFiles async operation is now done
// final value is in urls variable here
// you can use it here and ONLY here
// Note: this code here will get executed LONG after the
// handleFileSelect() function has already finished executing
}
});
// Only process image files
if (!f.type.match('image.*')) {
$('#list').append('<img class="file-thumb" src="/static/download168.png"/>');
continue;
}
var reader = new FileReader();
//Closure to capture file information
reader.onload = (function (theFile) {
return function (e) {
//Render thumbnail
$('#list').append('<img class="thumb" src="' + e.target.result + '" title="' + escape(theFile.name) + '"/>');
};
})(f);
reader.readAsDataURL(f);
}
}
// You can't use the urls variable here. It won't be set yet.
哦 请从您的ajax调用中删除async: false
。 出于多种原因,这是一件可怕的事情。
这是使用内置在jQuery中的Promise的版本:
document.getElementById('question-file-selector').addEventListener('change', handleFileSelect, false);
function handleFileSelect(evt) {
var files = evt.target.files; //File list object
// Loop through file list, render image files as thumbnails
var promises = [];
for (var i = 0, f; f = files[i]; i++) {
promises.push(handleFiles(f));
// Only process image files
if (!f.type.match('image.*')) {
$('#list').append('<img class="file-thumb" src="/static/download168.png"/>');
continue;
}
var reader = new FileReader();
//Closure to capture file information
reader.onload = (function (theFile) {
return function (e) {
//Render thumbnail
$('#list').append('<img class="thumb" src="' + e.target.result + '" title="' + escape(theFile.name) + '"/>');
};
})(f);
reader.readAsDataURL(f);
}
$.when.apply($, promises).then(function() {
var results = Array.prototype.slice.call(arguments);
// all handleFiles() operations are complete here
// results array contains list of URLs (some could be empty if there were errors)
});
}
function handleFiles(file) {
var filename = file.name;
return $.ajax({
type: 'GET',
data: {
"filename": file.name,
"FileType": "question_file"
},
url: '/dashboard/generateuploadurl/',
contentType: "application/json",
dataType: "json"
}).then(function(data) {
if (data.UploadUrl) {
console.log("upload url successfully created for " + file.name + " file");
console.log(data.UploadUrl);
return handleUpload(data.UploadUrl, file, data.Filename);
}
}, function(err) {
console.log("error occured while creating upload url for " + file.name + ' file');
console.log(err);
// allow operation to continue upon error
});
}
function handleUpload(UploadUrl, file, Filename) {
return $.ajax({
xhr: xhr_with_progress,
url: UploadUrl,
type: 'PUT',
data: file,
cache: false,
contentType: false,
processData: false
}).then(function(data) {
console.log('https://7c.ssl.cf6.rackcdn.com/' + Filename);
return 'https://7c.ssl.cf6.rackcdn.com/' + Filename;
}, function(err) {
console.log("error occured while uploading " + file.name);
console.log(err);
// allow operation to continue upon error
});
}
由于我无法运行此代码对其进行测试,因此这里可能会出现一两个错误,但是您应该能够调试这些错误或告诉我们错误发生的位置,我们可以帮助您对其进行调试。 从概念上讲,这是您解决协调多个异步操作的这类问题的方式。
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