An elegant / performant way to "Touch" a file in (update ModifiedTime) in WinRT?

Question

An elegant / performant way to "Touch" a file in (update ModifiedTime) WinRT?

I have some code which needs to delete files that are older than 30 days. This works well, but in some cases, I need to update the time on the file to reset the 30 day window, and prevent deletion. On the basicProperties list, the ModifiedTime is read-only, so I need to find another way to update it...

Method 1: Rename twice

    // Ugly, and may have side-effects depending on what's using the file
    // Sometimes gives access denied...
    public static async Task TouchFileAsync(this StorageFile file)
    {
       var name = file.Name;
       await file.RenameAsync("~" + name).AsTask().ContinueWith(
            async (task) => { await file.RenameAsync(name); }
       );
    }

Method 2: Modify a file property

    // Sometimes works, but currently throwing an ArgumentException for
    // me, and I have no idea why. Also tried many other properties:
    // http://msdn.microsoft.com/en-us/library/windows/desktop/bb760658(v=vs.85).aspx
    public static async Task TouchFileAsync(this StorageFile file)
    {
        var prop = new KeyValuePair<string, object>("System.Comment", DateTime.Now.Ticks.ToString());
        await file.Properties.SavePropertiesAsync(new[] { prop });
    }

Method 3: Use a Win32 API via P/Invoke?

Not sure if this would work on ARM devices?
Pass certification?
Be performant?
Is there a best way to do this? Code sample?

Anyone got any other ideas? I'm a bit stuck :-)

Many thanks, Jon

What is the Argument Exception? Also, why are you adding a generic comment, is that just for the example or is the process for deletion as trivial as "the doc hasnt been vhanged in x days"? — Zack Weiner, Oct 12 '12 at 13:56
I agree that comment isn't the best. It was a late night ;-) The exception was a vanilla ArgumentException with a really generic HResult (sorry, cant remember what). No helpful error message was attached. — Jon Rea, Oct 15 '12 at 15:58

score 2 · Answer 1 · answered Jan 09 '15 at 16:21

I just had a need for this and here is my solution.

usage

await storageFileToTouch.TouchAsync();

code

public static class StorageFileExtensions
{
    /// <summary>
    ///     Touches a file to update the DateModified property.
    /// </summary>
    public static async Task TouchAsync(this StorageFile file)
    {
        using (var touch = await file.OpenTransactedWriteAsync())
        {
            await touch.CommitAsync();
        }
    }
}

score 1 · Answer 2 · answered Oct 12 '12 at 14:20

Assuming you're planning on combing a list of files that exist locally on an RT machine, and not somewhere in that cloud (otherwise we woudln't have to worry about the WinRT doc mod process), You could easily use the Application Data Container provided to each app to store very thin data (key value pairs fit very well).

In this way you would store a future delete date for each file that needed to be persisted, so that the next time it was raised for deletion, before the deletion process occurs, the app checks the App Storage Data. Then you wont need to worry about the permissions of the files you're iterating over, when you're only trying to make sure they don't get deleted from your process.

Windows.Storage.ApplicationDataContainer localSettings = Windows.Storage.ApplicationData.Current.LocalSettings;

// Create a setting in a container

Windows.Storage.ApplicationDataContainer container = 
   localSettings.CreateContainer("FilesToPersist", Windows.Storage.ApplicationDataCreateDisposition.Always);

StorageFile file = fileYouWantToPersist; 

if (localSettings.Containers.ContainsKey("FilesToPersist"))
{

   localSettings.Containers["FilesToPersist"].Values[file.FolderRelativeId] = DateTime.Now.AddDays(30);
}

// Read data from a setting in a container

bool hasContainer = localSettings.Containers.ContainsKey("FilesToPersist");
bool hasSetting = false;

if (hasContainer)
{
   hasSetting = localSettings.Containers["FilesToPersist"].Values.ContainsKey(file.FolderRelativeId);
    if(hasSettings)
    {
         string dt =    localSettings.Containers["FilesToPersist"].Values[file.FolderRelativeId];
         if(Convert.ToDateTime(dt) < DateTime.Now)
         {
             //Delete the file
         }
    }
}

Resources:

http://msdn.microsoft.com/en-us/library/windows/apps/windows.storage.applicationdata.aspx

http://lunarfrog.com/blog/2011/10/10/winrt-storage-accesscache/

I agree that would work, and +1 for a creative alternative. However pushing a long list of files into an AppSettings bucket isn't really what I had in mind. After browsing around, and asking a Microsoft contact, I don't actually think it's possible. Apparently, it's actually by-design, as they want to disallow artificial manipulation of the file-system. Eventually we went with an alternative solution using our application's database, which removed the need to change the files modified-date. — Jon Rea, Oct 15 '12 at 15:51

An elegant / performant way to "Touch" a file in (update ModifiedTime) in WinRT?

2 Answers2