Javascript文件删除和读取目录-异步递归 [英] Javascript file dropping and reading directories - Asynchronous Recursion
问题描述
因此,我正在尝试创建文件删除器Web应用程序.现在,用户可以将文件拖放到屏幕上,而我可以读取它们,包括已删除目录中的所有文件.但是,我不知道脚本何时读完文件.
So I'm trying to create a file dropper web application. Right now, a user can drop files on the screen and I can read them, including all the files in a directory that was dropped. But, I don't know when the script is done reading the files.
一些代码:
第一个函数处理一个'drop'事件,并将循环遍历每个文件,并将其发送到另一个将读取其内容的函数.
This first function handles a 'drop' event and will loop through each file and send it to another function that will read its contents.
function readDrop( evt )
{
for( var i = 0; i < evt.dataTransfer.files.length; i++)
{
var entry = evt.dataTransfer.items[i].webkitGetAsEntry();
if(entry)
readContents(entry, "");
}
//Do stuff after all files and directories have been read.
}
此函数是递归FileEntry读取器.如果是文件,我将读取FileEntry.如果它是目录,它将循环浏览内容并通过此函数.
This function is a recursive FileEntry reader. If it is a file, I will read the FileEntry. If it is a directory, it will loop through the contents and pass it through this function.
function readContents(entry, path)
{
if( entry.isFile )
{
readFileData( entry, path, function(fileData)
{
_MyFiles.push( fileData );
});
}
else if( entry.isDirectory )
{
var directoryReader = entry.createReader();
var path = path + entry.name;
directoryReader.readEntries(function(results)
{
for( var j = 0; j < results.length; j++ )
{
readContents(entry, path);
}
}, errorHandler)
}
}
这是我读取文件的功能.回调只是将fileData对象推送到全局数组
And here is my function for reading the files. The callback just pushes the fileData object to a global array
function readFileData(entry, path, callback)
{
var fileData = {"name": entry.name, "size": 0, "path": path, "file": entry};
entry.file(function(file)
{
fileData["size"] = file.size;
callback( fileData );
}
}
我不确定该从哪里去,以便在读取所有文件和目录后可以进行回调.
I'm not sure where to go from here so that I can have a callback when all files and directories have been read.
推荐答案
FileSystem API似乎不太适合完全递归遍历的任务,这也许就是其他供应商未采用它的部分原因.无论如何,通过Promises的神秘组合,我认为我能够实现这一目标:
The FileSystem API doesn't seem well suited for the task of a full recursive traversal, perhaps that's part of the reason why other vendors are not adopting it. Anyway, with an arcane combination of Promises I think I was able to accomplish this goal:
function traverse_directory(entry) {
let reader = entry.createReader();
// Resolved when the entire directory is traversed
return new Promise((resolve_directory) => {
var iteration_attempts = [];
(function read_entries() {
// According to the FileSystem API spec, readEntries() must be called until
// it calls the callback with an empty array. Seriously??
reader.readEntries((entries) => {
if (!entries.length) {
// Done iterating this particular directory
resolve_directory(Promise.all(iteration_attempts));
} else {
// Add a list of promises for each directory entry. If the entry is itself
// a directory, then that promise won't resolve until it is fully traversed.
iteration_attempts.push(Promise.all(entries.map((entry) => {
if (entry.isFile) {
// DO SOMETHING WITH FILES
return entry;
} else {
// DO SOMETHING WITH DIRECTORIES
return traverse_directory(entry);
}
})));
// Try calling readEntries() again for the same dir, according to spec
read_entries();
}
}, errorHandler );
})();
});
}
traverse_directory(my_directory_entry).then(()=> {
// AT THIS POINT THE DIRECTORY SHOULD BE FULLY TRAVERSED.
});
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