DirectoryReaderSync - Web APIs 编辑

Non-standard

This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The DirectoryReaderSync interface of the File System API lets you read the entries in a directory.

This interface has been abandonned: it was on a standard track and it proves not a good idea. Do not use it anymore.

About this document

This document was last updated on March 2, 2012 and follows the W3C Specifications (Working Draft) drafted on April 19, 2011.

This specification is pretty much abandoned, having failed to reach any substantial traction.

Basic concepts

Before you call the only method in this interface, readEntries(), create the DirectoryEntrySync object. But DirectoryEntrySync (as well as FileEntrySync) is not a data type that you can pass between a calling app and Web Worker thread. It's not a big deal, because you don't really need to have the main app and the worker thread see the same JavaScript object; you just need them to access the same files. You can do that by passing a list of  filesystem: URLs—which are just strings—instead of a list of entries. You can also use the filesystem: URL to look up the entry with resolveLocalFileSystemURL(). That gets you back to a DirectoryEntrySync (as well as FileEntrySync) object.

Example

In the following code snippet from HTML5Rocks, we create Web Workers and pass data from it to the main app.

// Taking care of the browser-specific prefixes.
  window.resolveLocalFileSystemURL = window.resolveLocalFileSystemURL ||
                                     window.webkitResolveLocalFileSystemURL;

// Create web workers
  var worker = new Worker('worker.js');
  worker.onmessage = function(e) {
    var urls = e.data.entries;
    urls.forEach(function(url, i) {
      window.resolveLocalFileSystemURL(url, function(fileEntry) {
        // Print out file's name.
        console.log(fileEntry.name);
      });
    });
  };

  worker.postMessage({'cmd': 'list'});

The following is Worker.js code that gets the contents of the directory.

// Taking care of the browser-specific prefixes.
self.requestFileSystemSync = self.webkitRequestFileSystemSync ||
                             self.requestFileSystemSync;

// Global for holding the list of entry file system URLs.
var paths = [];

function getAllEntries(dirReader) {
  var entries = dirReader.readEntries();

  for (var i = 0, entry; entry = entries[i]; ++i) {
    // Stash this entry's filesystem in URL
    paths.push(entry.toURL());

    // If this is a directory, traverse.
    if (entry.isDirectory) {
      getAllEntries(entry.createReader());
    }
  }
}

// Forward the error to main app.
function onError(e) {
  postMessage('ERROR: ' + e.toString());
}

self.onmessage = function(e) {
  var data = e.data;

  // Ignore everything else except our 'list' command.
  if (!data.cmd || data.cmd != 'list') {
    return;
  }

  try {
    var fs = requestFileSystemSync(TEMPORARY, 1024*1024 /*1MB*/);

    getAllEntries(fs.root.createReader());

    self.postMessage({entries: paths});
  } catch (e) {
    onError(e);
  }
};

Method overview

Method

readEntries()

Returns a lost of entries from a specific directory. Call this method until an empty array is returned.

EntrySync readEntries (
) raises (FileException);

Returns

Parameter

None

Exceptions

This method can raise a FileException with the following codes:

Browser compatibility

BCD tables only load in the browser

See also

Specification: File API: Directories and System SpecificationWD

Reference: File System API

Introduction: Basic Concepts About the File System API