在 iOS Phonegap 应用程序上序列化文件传输
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【中文标题】在 iOS Phonegap 应用程序上序列化文件传输【英文标题】:Serialising file transfers on iOS Phonegap application 【发布时间】:2012-10-04 19:32:01 【问题描述】:我有一个适用于 ios 的 phonegap 应用程序,它从服务器下载图像和 pdf 文件,因为它们必须在本地可用。
我使用 jQuery 解析以找到我需要下载的资产列表,然后使用 Phonegap API 启动 FileTransfer,如下所示:
// assets is an array that has all pdf and image urls to be downloaded.
assets.map(downloadFile);
function downloadFile(file_url)
console.log('Downloading file:'+file_url);
var fileTransfer = new FileTransfer();
fileTransfer.download(
file_url,
get_local_file_path(file_url),
download_success,
function(error)
stopspin();
console.log('ERROR downloading: '+ error.source);
$('#notify-user').html('Downloading failed. <a href="#" onclick="checkLatestIssue()">Try again?</a>')
);
现在,资产每次最多可以有 50 个。我可以看到所有文件传输请求都是立即发送的,有时,某些文件传输请求会超时,从而使我无法通过本地资源渲染下载。
有没有一种方法可以使所有这些问题的连续下载与大约 5 次并行下载?
【问题讨论】:
【参考方案1】:我在我的应用程序上所做的是创建一个需要下载的文件的全局数组,然后启动从数组前面抓取第一个元素并下载它的代码。完成后,它会检查数组中是否还有要处理的项目,如果是,则重新开始该过程。如果没有,它会完成下载并继续执行应用程序接下来需要执行的任何操作。
为我们的文件创建一个空白数组以供下载
data_to_process = [];
将图像和视频添加到从 API 返回的“结果”数组中
// add images to array
$.each( result.images_to_download, function( index, value )
index = index + 1;
data_to_process.push(
"type": "images",
"filename": value,
"msg": "Downloading image "+index+" of "+result.images_to_download.length+"..."
);
);
// add videos to array
$.each( result.videos_to_download, function( index, value )
index = index + 1;
data_to_process.push(
"type": "videos",
"filename": value,
"msg": "Downloading video "+index+" of "+result.videos_to_download.length+"..."
);
);
这是处理文件的代码 注意:这里有一些不需要的代码,用于根据文件的内容将文件放在某些目录中,更新下载进度的百分比指示器等:
// values for percentages
start_data_length = data_to_process.length;
current_iteration = 0;
// set writing to false
writing = false;
// what we do after each iteration in the data array
var finish_processing = function()
// increment iteration count
current_iteration++;
// set percent value
var percent = current_iteration / start_data_length * 100;
percent = Math.round( percent );
$('#update_percent').html( percent );
// remove from array after process
data_to_process.splice( 0, 1 );
// set writing back to false so we can start another iteration
writing = false;
// checks if we need to process the next part of the array or not
var check_to_process = function()
// console.log('checking if we need to process');
// if we still have items in the array to process
if ( data_to_process.length > 0 )
// if we're currently not working on an item
if ( writing === false )
// process next item in array
process_download_data();
else
// not ready yet, wait .5 seconds and check again
// console.log('busy - waiting to process');
setTimeout( check_to_process, 500 );
else
// console.log('nothing left to process');
// processes the downloaded data
var process_download_data = function()
// set writing to true
writing = true;
// current item to process is first item in array
var current_item = data_to_process[0];
if ( current_item.msg )
$('#update_item').html(current_item.msg);
else
$('#update_item').html('Processing update data...');
// console.log( 'processing this: '+ current_item.filename );
// if something didn't work right..
var broke = function(error)
// console.log( 'error' );
// console.log( error );
// cycle to next item in array
finish_processing();
// get the directory of current item's "type"
var get_directory = function( fileSystem )
fileSystem.root.getDirectory( current_item.type, create:true,exclusive:false, get_file, broke );
// get the file
var get_file = function( dirEntry )
// if texts
if ( current_item.type == 'texts' )
dirEntry.getFile( current_item.filename+".txt", create: true, exclusive: false, create_text_writer, broke);
// if images
else if ( current_item.type == 'images' )
var localFileName = current_item.filename.substring(current_item.filename.lastIndexOf('/')+1);
dirEntry.getFile( localFileName, create: true, exclusive: false, create_file_writer, broke);
// if videos
else if ( current_item.type == 'videos' )
var localFileName = current_item.filename.substring(current_item.filename.lastIndexOf('/')+1);
dirEntry.getFile( localFileName, create: true, exclusive: false, create_file_writer, broke);
// if audios
else if ( current_item.type == 'resources' )
var localFileName = current_item.filename.substring(current_item.filename.lastIndexOf('/')+1);
dirEntry.getFile( localFileName, create: true, exclusive: false, create_file_writer, broke);
// if audios
else if ( current_item.type == 'audios' )
var localFileName = current_item.filename.substring(current_item.filename.lastIndexOf('/')+1);
dirEntry.getFile( localFileName, create: true, exclusive: false, create_file_writer, broke);
// write to file using filetransfer
var create_file_writer = function( fileEntry )
if ( current_item.remove === true )
fileEntry.remove( function(entry)
// what to do when image is deleted
finish_processing();
,broke);
else
var localPath = fileEntry.fullPath;
// console.log('Writing to: '+localPath+' from: '+current_item.filename);
var ft = new FileTransfer();
ft.download( current_item.filename, localPath, function(entry)
// what to do when image is downloaded
finish_processing();
,broke);
// create writer for "texts" type
var create_text_writer = function( fileEntry )
fileEntry.createWriter( write_text_file, broke );
// write to file for "texts" type
var write_text_file = function( writer )
// write new contents
writer.write( current_item.data );
// add item where it needs to be in the document
if ( current_item.append === true )
$('#'+current_item.marker).nextAll().remove();
// appending
// console.log('Appending data to: #'+current_item.id);
$('#'+current_item.id).append( current_item.data );
else
// adding
// console.log('Adding data to: #'+current_item.id);
$('#'+current_item.id).html( current_item.data );
// console.log('finished writing: '+current_item.filename);
finish_processing();
// request persistent filesystem
window.requestFileSystem( LocalFileSystem.PERSISTENT, 0, get_directory, broke );
// check if we need to process the next item yet
check_to_process();
// process data from the update
process_download_data();
【讨论】:
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