UWP Check If File Exists

Question

I am currently working on a Windows 10 UWP App. The App needs to Check if a certain PDF File exists called "01-introduction", and if so open it. I already have the code for if the file does not exist. The Code Below is what i currently have:

        try
        {
            var test = await DownloadsFolder.CreateFileAsync("01-Introduction.pdf", CreationCollisionOption.FailIfExists); 
        }
        catch
        {

        }

This code Does not work correctly because to check if the file exists here, I attempt to create the file. However if the file does not already exist an empty file will be created. I do not want to create anything if the file does not exist, just open the PDF if it does.

If possible, i would like to look inside a folder which is in the downloads folder called "My Manuals".

Any help would be greatly appreciated.

Solution 1

public async Task<bool> IsFilePresent(string fileName)
{
    var item = await ApplicationData.Current.LocalFolder.TryGetItemAsync(fileName);
    return item != null;
}

But not support Win8/WP8.1

https://blogs.msdn.microsoft.com/shashankyerramilli/2014/02/17/check-if-a-file-exists-in-windows-phone-8-and-winrt-without-exception/

Solution 2

There are two methods

1) You can use StorageFolder.GetFileAsync() as this is also supported by Windows 8.1 and WP 8.1 devices.

try
{
   StorageFile file = await DownloadsFolder.GetFileAsync("01-Introduction.pdf");
}
catch
{
    Debug.WriteLine("File does not exits");
}

2) Or you can use FileInfo.Exists only supported for windows 10 UWP.

FileInfo fInfo = new FileInfo("01-Introduction.pdf");
if (!fInfo.Exists)
{
    Debug.WriteLine("File does not exits");
}

Solution 3

System.IO.File.Exists is UWP way too. I test now in Windows IOT. it just works.

Solution 4

This helped me in my case:

ApplicationData.Current.LocalFolder.GetFileAsync(path).AsTask().ContinueWith(item => { 
    if (item.IsFaulted)
        return; // file not found
    else { /* process file here */ }
});

Solution 5

This worked for me running my UWP C# app on Windows 10...

    StorageFolder app_StorageFolder = await StorageFolder.GetFolderFromPathAsync( @App.STORAGE_FOLDER_PATH );
    var item = await app_StorageFolder.TryGetItemAsync(relative_file_pathname);
    return item != null;

View more solutions

Comments

[Jay Zuo]

Is the "Swift Manuals" folder created by your app? By default, your app can only access files and folders in the user's Downloads folder that your app created. However, you can gain access to files and folders in the user's Downloads folder by calling a file picker (FileOpenPicker or FolderPicker) so that users can navigate and pick files or folders for your app to access.

[James Tordoff]

@JayZuo-MSFT Thank you for the clarification Jay. This is the problem we have been coming across. So we can get directory access to Downloads. We need to look at another approach and do a little more reading.

[Jay Zuo]

If you create a file or folder in the Downloads folder, we recommend that you add that item to your app's FutureAccessList so that your app can readily access that item in the future. For more info, please see File access permissions.

[James Tordoff]

Unfortunately (1) does not seem available within Windows 10 UWP there is no Definition ofr GetFileAsync for DownloadsFolder. (2) seems to be just what I am looking for, unfortunately I always return False, how do I specify which folder is to be searched for the FileInfo. I am only supporting Win10 and not backwards compatible at all.

[James Tordoff]

Thanks Ben, both you and Absolute have hit in the right direction, but unfortunately I am currently only returning False, I have commented above with Absolute, how can I confirm which Directory/Folder is being searched for the FileInfo ?

[AbsoluteSith]

Are you sure DownloadFolder is a StorageFolder type, if so it should have a definition. Try pasting your entire code, I'll check it out

[Archana]

DownloadFolder doesnt have GetFileAsync () method

[Ben Steele]

I think you may need to use the getfile functions to see if they return an object or null. Answer updated

[Peter Torr - MSFT]

That is not the Downloads folder.

[Reynevan]

It will throw an exception when the item is not found.

[lindexi]

@Reynevan It doesn't throw an exception.

[CBHacking]

If you're going to use System.IO at all, you might as well use System.IO.File.Exists(String). It's more efficient - no need to construct an object - and simpler to read.

[CBHacking]

While not "the UWP way" (in particular, it does an I/O operation - albeit a very fast one - synchronously), this is a viable option on UWP (Win10) apps. Just be aware that the app will not have any kind of lock on the file; if another thread or process removes or creates the file between check and use, you could get unexpected (and potentially harmful) behavior.

[DirtyNative]

Indeed, it does not throw any Exception, altought the Docs say they do

[visc]

This fails on files when paths are too long: stackoverflow.com/questions/11210408/…

[Wagner Bertolini Junior]

@visc on the Thread you an see on a comment that this method is expected to return false when any errors occurs when trying to reach file. So, if the system treats "path to long" as an error, this method is still right. The solution presented on the other thread is inefficient as the author confirms, I tried here to present the most "elegant" solution. And it works on 99.9% of times, so I don´t think its useful to integrate that solution on this proposal.

[Filipe Madureira]

This is not the downloads folder but the local app folder which gets overwritten between deployments and updates, beware.

[Weissu]

Have to remember that TryGetItemAsync returns Files AND Folders. Need to check type of returned item like item.IsOfType(StorageItemTypes.File).

[Alamakanambra]

This is the best solution, since you don't have to catch any exception here and it works with StorageFolder class.

[Sean O'Neil]

@CBHacking This is actually not true. It only works in the app's LocalFolder (and probably LocalCache and Temp). Even if you have access to another folder using the picker or a capability, System.IO stuff won't work there.

[Sean O'Neil]

No, it only works in LocalFolder, LocalCache, etc. Even if you grant access to another folder/file using the picker, or use a special folder (like Downloads in the question) the System.IO methods won't work there.

[CBHacking]

@SeanO'Neil That's false for a few reasons. First, you can absolutely use System.IO.File to access files outside the app storage, such as in the system directory or, with the right capabilities defined, locations such as removable storage. Second, you can test for existence of files you can't even access; you'll get a different error for "file not found" vs. "access denied". Third, even if if checking app-specific files, an appcontainer can have multiple processes (e.g. background audio process) and any process can have multiple threads, so you do risk TOCTOU bugs.

[CBHacking]

... Well. At some point they decided to make Access Denied errors return false for File.Exists(), which is a lie. You CAN still (I just checked) try to open or stat the file (File.GetFileAttributes() works even if you don't have read permissions; so does opening the file without requesting any access but you can't do that using System.IO.File). That will either work or throw an exception; FileNotFound or DirectoryNotFound mean the file doesn't exist, UnauthorizedAccess means it does.

[Sean O'Neil]

@CBHacking Yeah File.Exists, EnumerateFiles, etc. hasn't worked as long as I remember. Perhaps as you say it used to. I forgot to mention it does, however, work on exFAT file systems, just not on NTFS.

[Sean O'Neil]

Never tried GetFileAttributes, it would be interesting to see if that's faster than the Windows.Storage way of doing it.