In a Silverlight app I need to download a large amount of files. When a file finished downloading I need to update an ObservableCollection object. This is the code I am using :
private void downloadFiles(List<string> files)
{
foreach (var file in files)
{
string _file = file;
new WebClient().OpenReadTaskAsync(new Uri(_file)).ContinueWith(t1 =>
{
Stream stream = t1.Result;
byte[] buffer = new byte[stream.Length];
stream.ReadAsync(buffer, 0, (int)stream.Length).ContinueWith(t2 =>
{
myObservableCollection.Add(_file); //An Exception is thrown.
});
});
}
}
When trying to add to myObservableCollection An exception is thrown:
Cannot change ObservableCollection during a CollectionChanged or PropertyChanged event.
One way to fix that is to await on each OpenReadTaskAsync, but then I won't be maximizing the I/O. I also came across a ReaderWriterLock which look like it can help, but unfortunately it's not avaible in Silverlight.
How can I handle this issue ?
You could serialize updating the ObservableCollection on the UI thread using this:
string _file = file;
var ui = TaskScheduler.FromCurrentSynchronizationContext();
...
.ContinueWith(t2 =>
{
myObservableCollection.Add(_file); //An Exception is thrown.
}
, ui );
Related
This one is hard to explain, so I give you some actual and pseudo code:
try
{
// If source (a string) points towards a file that is available with
// StorageFile.GetFileFromPathAsync(), just open the file that way.
// If that is not possible, use the path to look up an Access Token
// and use the file from the StorageFolder gotten via that token.
StorageFile file = await GetFileFromAccessList(source);
if (file != null)
{
bitmap = new BitmapImage();
using (IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.Read))
{
await bitmap.SetSourceAsync(fileStream);
}
}
}
catch (Exception e)
{
string s = e.Message;
bitmap = null;
}
with the following method:
public async Task<StorageFile> GetFileFromAccessList(string path)
{
StorageFile result = null;
if (String.IsNullOrEmpty(path) == false)
try
{
// Try to access to file directly...
result = await StorageFile.GetFileFromPathAsync(path);
}
catch (Exception)
{
result = null;
try
{
// See if the folder this thing is in is in the access list...
StorageFolder folder = await GetFolderFromAccessList(Path.GetFullPath(path));
// If there is a folder, try that.
if (folder != null)
result = await folder.GetFileAsync(Path.GetFileName(path));
}
catch (Exception)
{
result = null;
}
}
return result;
}
The resulting bitmap is used in Image.SetSource() as an ImageSource.
Now what kills me: this call works perfectly, fast and rock solid for files stored within the apps folder or KnownFolders. So it works like a charm when I don't need an Access Token. Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.GetFolderAsync(token)
However, it breaks if I have to use an access token, just not all the time
This code does not break immediately: it breaks when I try to open more than 5-7 source files at the same time.
Repeat that: this works if I display 5-7 images. If I try to open more, it freezes the PC. No such problem occurs when I open StorageFiles without tokens.
I can access such files using normal file operations. I can create bitmaps from them, process them, the work.
I just cannot make them a source of an XAML Image.
Any thoughts?
Ah clarity.
So it turns out that using the DataContextChanged event to refresh the bitmap through Image.SetSource() is the murder weapon.
The solution: declare a property of type BitmapSource. Bind the Image.Source to that property. Update the property with the loaded bitmap upon Image.Loaded and Image.DataContextChanged. Works stable and fast now in all conditions I was able to test.
I have register a global exception handler, and it fires and contains all of the information I need with the exception of the Request.Content which is always empty... I need the values that were passed in when I am debugging...
Public class MyExceptionLogger : ExceptionLogger
{
public override void Log(ExceptionLoggerContext context)
{
try
{
... other code
var methodName = context.Request.Method.ToString();
var errorUri = context.Request.RequestUri.ToString();
var errorMessage = context.Exception.Message;
var errorStackTrace = context.Exception.StackTrace.ToString();
var payload = context.Request.Content.ReadAsStringAsync().Result;
..... other code
}
}
}
What is the proper way to retrieve the Request.Content from global error handler ? In the code above the Content property has already been read by the model binders and as such is always empty.
How can I consistently get the posted body from an exception ?
Should I retrieve and save the posted body in a custom MessageHandler ?
Thanks
Greg
In experimenting with reading the buffer of the request.Content in a custom message handler.. It appears that if I read it with this code:
var payload = context.Request.Content.ReadAsStringAsync().Result;
and do NOTHING with it... The buffer will not be emptied when the model binders read it, because its always there in my exception logger now... I don't know if this is by design or what but its exasperating !
just got some Problems with Loading Xaml Files by Runtime.
For your Information my Code-Snippet to Load the File as Content of a Usercontrol:
public UserControl LoadXaml(FileInfo paramFile)
{
FileInfo _XamlFile = paramFile;
UIElement rootElement;
FileStream s = new FileStream(_XamlFile.FullName, FileMode.Open);
rootElement = (UIElement)XamlReader.Load(s);
s.Close();
UserControl uc = new UserControl();
if (rootElement.GetType() == typeof(Window))
{
uc.Content = (rootElement as Window).Content;
}
else
{
uc = rootElement as UserControl;
}
return uc;
}
private void lstPDFDokumente_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var _XamlFile = ((System.Windows.Controls.ListBox)sender).SelectedItem as FileInfo;
if (_XamlFile != null)
{
layoutGrid.Children.Clear();
System.Windows.Controls.UserControl rootElement;
rootElement = XamlController.LoadXaml(_XamlFile);
layoutGrid.Children.Add(rootElement);
}
}
This works fine while Events and x:Class="..." are deleted by hand.
The Problems I try to solve are:
If there is a x:Class="..." at the root element the XamlReader throws the first exception.
When the XamlReader reaches a Control which contains an event, for Example Click or TextChanged, it throws another Exception.
What i try to figure out is how to load a XamlFile, show it inside of a Control in the main Window and to show some of the attributes like Name,Height,Width and so on.
Just read dozens of Websites but never found a topic about to make a preview or things like that.
One of the solutions i tried is to read the Xaml File as XML and delete that code.
The Problem was to get a list of all possible Events in C#.
If there are some Questions to that Code, feel free to ask :)
Greetings
Daniel
I am trying to use the sitecore API to serialize and restore sitecore items. I have created a WCF app to retrieve an Item name given a ID or sitecore path (/sitecore/content/home), retrieve a list of the names of the items children give an id or path. I can also Serialize the content tree.
public void BackupItemTree(string id)
{
Database db = Sitecore.Configuration.Factory.GetDatabase("master");
Item itm = db.GetItem(id);
Sitecore.Data.Serialization.Manager.DumpTree(itm);
}
The above code works great. After running it can see that the content tree has been serialized.
However when I try to restore the serialized items useing the following:
public void RestoreItemTree(string path)
{
try
{
using (new Sitecore.SecurityModel.SecurityDisabler())
{
Database db = Sitecore.Configuration.Factory.GetDatabase("master");
Data.Serialization.LoadOptions opt = new Data.Serialization.LoadOptions(db);
opt.ForceUpdate = true;
Sitecore.Data.Serialization.Manager.LoadItem(path, opt);
//Sitecore.Data.Serialization.Manager.LoadTree(path, opt);
}
}
catch (Exception ex)
{
throw ex;
}
}
With this code I get no errors. It runs, but if I check SiteCore it didn't do anything. I have tested using the Office Core example. The path I sent in, which might be the issue is:
C:\inetpub\wwwroot\sitecoretest\Data\serialization\master\sitecore\content\Home\Standard-Items\Teasers\Our-Clients.item
and
C:\inetpub\wwwroot\sitecorebfahnestockinet\Data\serialization\master\sitecore\content\Home\Standard-Items\Teasers\Our-Clients
Neither seems to do anything. I changed the teaser title of the item and am trying to restore to before the but every time the change is still present.
Any help would be appreciated as the SiteCore documentation is very limited.
You can always check how the Sitecore code works using Reflector, the following method is called when you click "Revert Item" in back-end:
protected virtual Item LoadItem(Item item, LoadOptions options)
{
Assert.ArgumentNotNull(item, "item");
return Manager.LoadItem(PathUtils.GetFilePath(new ItemReference(item).ToString()), options);
}
In LoadOptions you can specify whether you want to overwrite ("Revert Item") or just update ("Update Item") it.
See Sitecore.Shell.Framework.Commands.Serialization.LoadItemCommand for more info.
You have the correct LoadOptions for forcing an overwrite (aka Revert).
I suspect that the path you are using for the .item file wrong. I would suggest modifying your method to take a path to a Sitecore item. Using that path, you should leverage other serialization APIs to determine where the file should be.
public void RestoreItemTree(string itemPath)
{
Sitecore.Data.Database db = Sitecore.Configuration.Factory.GetDatabase("master");
Sitecore.Data.Serialization.ItemReference itemReference = new Sitecore.Data.Serialization.ItemReference(db.Name, itemPath);
string path = Sitecore.Data.Serialization.PathUtils.GetFilePath(itemReference.ToString());
Sitecore.Data.Serialization.LoadOptions opt = new Sitecore.Data.Serialization.LoadOptions(db);
opt.ForceUpdate = true;
using (new Sitecore.SecurityModel.SecurityDisabler())
{
Sitecore.Data.Serialization.Manager.LoadItem(path, opt);
}
}
Took me a while to work out, but you have to remove .item when restoring the tree
try this
public void RestoreItemTree(string itemPath)
{
var db = Factory.GetDatabase("master");
var itemReference = new ItemReference(db.Name, itemPath);
var path = PathUtils.GetFilePath(itemReference.ToString());
if (!System.IO.File.Exists(path))
{
throw new Exception("File not found " + path);
}
var opt = new LoadOptions(db);
opt.ForceUpdate = true;
using (new SecurityDisabler())
{
Manager.LoadItem(path, opt);
Manager.LoadTree(path.Replace(".item", ""), opt);
}
}
I have a simple WCF service that exposes a REST endpoint, and fetches files from a BLOB container. The service returns the file as a stream. i stumbled this post about closing the stream after the response has been made :
http://devdump.wordpress.com/2008/12/07/disposing-return-values/
This is my code:
public class FileService
{
[OperationContract]
[WebGet(UriTemplate = "{*url}")]
public Stream ServeHttpRequest(string url)
{
var fileDir = Path.GetDirectoryName(url);
var fileName = Path.GetFileName(url);
var blobName = Path.Combine(fileDir, fileName);
return getBlob(blobName);
}
private Stream getBlob(string blobName)
{
var account = CloudStorageAccount.FromConfigurationSetting("ConnectingString");
var client = account.CreateCloudBlobClient();
var container = client.GetContainerReference("data");
var blob = container.GetBlobReference(blobName);
MemoryStream ms = new MemoryStream();
blob.DownloadToStream(ms);
ms.Seek(0, SeekOrigin.Begin);
return ms;
}
}
So I have two question :
Should I follow the pattern mentioned in the post ?
If I change my return type to Byte[], what are Cons/Pros ?
( My client is Silverlight 4.0, just in case it has any effect )
I'd consider changing your return type to byte[]. It's tidier.
Stream implements IDisposable, so in theory the consumer of your method will need to call your code in a using block:
using (var receivedStream = new FileService().ServeHttpRequest(someUrl))
{
// do something with the stream
}
If your client definitely needs access to something that Stream provides, then by all means go ahead and return that, but by returning a byte[] you keep control of any unmanaged resources that are hidden under the covers.
OperationBehaviorAttribute.AutoDisposeParameters is set to TRUE by default which calls dispose on all the inputs/outputs that are disposable. So everything just works.
This link :
http://devdump.wordpress.com/2008/12/07/disposing-return-values/
explains how to manually control the process.