网络应用程序对于数据收集/摄取很有用。如果收集和存储数据的机制易于使用，则可以积累大量有用的数据进行数据处理。将数据从一个位置移动到另一个位置的一种简单方法是 Web 应用程序上的拖放功能。
在这篇文章中，我展示了三个示例，说明如何使用 JavaScript 拖放编程来移动和存储 HTML 元素数据和文件。
<!DOCTYPE html>
<html>
<head></head>
<body>
<h1>Example 0: Drag and Drop HTML text/elements</h1>
<div id="HTML_text" draggable="true" class="dragElement">HTML text</div>
<br><br>
<div id="dropArea" class="dropArea"> Drop for Example 0 & 1</div>
<style>
.dropArea { height: 200px;
width: 200px;
border-radius: 15px;
border: 0.25px solid black;
background-color: #7084c4;
}
.HTML_text { cursor: move; }
</style>
<script>
var example;
var other_data_related_to_dragEvent = {};
var html_element_drag_list_metaData = [];
// ----------------------------------------------------
// Drag functionality: Example 0
// ----------------------------------------------------
document.getElementById("HTML_text").addEventListener("dragstart", processEvent_drag_example0, false);
// document.getElementById("HTML_text").addEventListener("dragend", processEvent_drag_example0, false); // to stop
function processEvent_drag_example0(event) {
example = 0;
event.dataTransfer.setData('text/plain', event.target.id);
}
// ----------------------------------------------------
// ----------------------------------------------------
// Drop functionality: Example 0 and 1
// ----------------------------------------------------
document.getElementById("dropArea").addEventListener("drop", processEvent_drop, false);
document.getElementById("dropArea").addEventListener("dragover", processEvent_dragover, false);
function processEvent_drop(event) {
// Stop defaults and allow drop events
event.preventDefault();
// Detects files dragged from pc
html_element_drag_list_metaData.push(event.dataTransfer.files);
console.log('html_element_drag_list_metaData: ', html_element_drag_list_metaData);
// Detects html elements dragged from the html page
const data = event.dataTransfer.getData('text/plain');
console.log('data: ', data);
if (data.length != 0) {
// find the draggable element based on the data
const dragElement = document.getElementById(data);
console.log('dragElement: ', dragElement);
// Append the draggable element
event.target.appendChild(dragElement);
}
}
function processEvent_dragover(event) {
// Stop defaults and allow drop events
event.preventDefault();
}
// -------------------------------------------------
</script>
</body>
</html>
在示例 0 中，HTML 文本元素实际上已移至放置区域。 HTML 文本的 div 的 id 出现在变量数据中，因此可以跟踪 dropArea 内的元素 id。此示例对于组织/存储在 Web 应用程序上编写的现有 html 非常有用，但在大多数数据摄取情况下，人们希望组织/存储来自不同位置的数据。
此示例是拖动 HTML 元素和拖动文件之间的交叉示例。可以使用“浏览”按钮选择一个文件；将文件拖到浏览按钮或单击浏览按钮选择文件。选择文件后会出现一个表情符号，表情符号的出现以 HTML 元素的形式表示该文件。然后可以将代表文件的 HTML 元素 emoji 拖到 dropArea 进行数据摄取/存储。
<!DOCTYPE html>
<html>
<head></head>
<body>
<h1>Example 1: Click button create drag and drop elements</h1>
<input type="file" id="upload_file" accept="audio/*" style="display:block" multiple>
<div id="file_name" style="display:none"></div>
<div id="base64_string" style="display:none"></div>
<div id="base64_string_icon" draggable="true" class="dragElement" style="display:none">?</div>
<br><br>
<div id="dropArea" class="dropArea"> Drop for Example 0 & 1</div>
<style>
.dropArea { height: 200px;
width: 200px;
border-radius: 15px;
border: 0.25px solid black;
background-color: #7084c4;
}
.HTML_text { cursor: move; }
</style>
<script>
var example;
var other_data_related_to_dragEvent = {};
var html_element_drag_list_metaData = [];
// ----------------------------------------------------
// Drag functionality: Example 1
// ----------------------------------------------------
// The eventlistener needs to be always running, to detect which file the user selected with browse
document.getElementById("upload_file").addEventListener("change", previewInput_drop, false);
async function previewInput_drop(event) {
// Take the first file
const file = event.target.files[0]; // first file in the list of selected files, better for selecting multiple files at one time
// console.log("file :", file);
document.getElementById("file_name").innerHTML = file.name;
// ---------------------
const reader = new FileReader();
reader.onload = async function(e){
document.getElementById("base64_string").innerHTML = e.target.result;
document.getElementById("base64_string_icon").style.display = "block";
}
reader.readAsDataURL(file);
}
document.getElementById("base64_string_icon").addEventListener("dragstart", processEvent_drag_example1, false);
function processEvent_drag_example1(event) {
example = 1;
event.dataTransfer.setData('text/plain', event.target.id);
}
// ----------------------------------------------------
// ----------------------------------------------------
// Drop functionality: Example 0 and 1
// ----------------------------------------------------
document.getElementById("dropArea").addEventListener("drop", processEvent_drop, false);
document.getElementById("dropArea").addEventListener("dragover", processEvent_dragover, false);
function processEvent_drop(event) {
// Stop defaults and allow drop events
event.preventDefault();
// Detects files dragged from pc
html_element_drag_list_metaData.push(event.dataTransfer.files);
console.log('html_element_drag_list_metaData: ', html_element_drag_list_metaData);
// Detects html elements dragged from the html page
const data = event.dataTransfer.getData('text/plain');
console.log('data: ', data);
if (data.length != 0) {
// find the draggable element based on the data
const dragElement = document.getElementById(data);
console.log('dragElement: ', dragElement);
// Append the draggable element
event.target.appendChild(dragElement);
}
}
function processEvent_dragover(event) {
// Stop defaults and allow drop events
event.preventDefault();
}
// -------------------------------------------------
</script>
</body>
</html>
在此示例中，可以一次高效地将多个文件拖动到 dropArea。
<!DOCTYPE html>
<html>
<head></head>
<body>
<h1>Example 2: Drag and drop files</h1>
<input type="file" id="upload_file_dragdrop" style="display:block" class="dropArea1" multiple>
<br><br>
<button id="use_moved_data" onclick="use_moved_data()">use_moved_data</button>
<!-- ---------------------------------------- -->
<!-- CSS -->
<style>
.dropArea1 { height: 200px;
width: 200px;
border-radius: 15px;
border: 0.25px solid black;
background-color: #56b06e;
}
</style>
<!-- ---------------------------------------- -->
<script>
var other_data_related_to_dragEvent = {};
var html_element_drag_list_metaData = [];
// ----------------------------------------------------
// Drag and Drop functionality: Example 2
// ----------------------------------------------------
document.getElementById("upload_file_dragdrop").addEventListener("change", previewInput, false);
async function previewInput(event) {
// For multiple files
const allFiles = event.target.files;
// console.log("allFiles :", allFiles);
var i = 0;
while (i < allFiles.length) {
const file = allFiles[i];
// console.log("file :", file);
await obtain_fileInfo(file)
.then(base64str => { other_data_related_to_dragEvent[file.name] = base64str; })
.catch(error => console.error(error));
i = i + 1;
}
// ---------------------
}
async function obtain_fileInfo(file) {
var base64_string = await new Promise((resolve) => {
const reader = new FileReader();
reader.onload = async function(e){
resolve(e.target.result); // inside resolve is the value that the function returns
};
reader.readAsDataURL(file);
});
return base64_string;
}
// ----------------------------------------------------
async function use_moved_data() {
console.log('html_element_drag_list_metaData: ', html_element_drag_list_metaData);
console.log('other_data_related_to_dragEvent: ', other_data_related_to_dragEvent);
}
</script>
</body>
</html>
我们可以看到拖入dropArea的三个文件的base64字符串数据！然后可以将 Base64 字符串数据保存为 Blob 对象并通过 Internet 传输。
我希望这些拖放 HTML 元素和文件的方法对某人有所帮助。
祝你练习愉快！ ？
？ GitHub | ？练习 Datscy @ Dev.to | ？练习 Datscy @ Medium
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