Develop Reference

How do I save a Text file on the Universal Windows Platform?

I'm trying to save my text file in UWP, but It always saving to different file. By the way I'm using MVVM architecture.
My Code
FileSavePicker savePicker = new FileSavePicker();
savePicker.SuggestedFileName = "New Text Document";
savePicker.SuggestedStartLocation = PickerLocationId.Desktop;
savePicker.FileTypeChoices.Add("Text Document", new List<string>() { ".txt" });
savePicker.DefaultFileExtension = ".txt";
StorageFile storageFile = await savePicker.PickSaveFileAsync();
if(storageFile != null)
{
CachedFileManager.DeferUpdates(storageFile);
await FileIO.WriteTextAsync(storageFile, Document.Text);
FileUpdateStatus updateStatus = await CachedFileManager.CompleteUpdatesAsync(storageFile);
Document.FileName = savePicker.SuggestedFileName;
Document.IsSaved = true;
}
My code is always saving texts on different file. I'm trying to save my text to same file.

In UWP there is a feature called FutureAccessList. It can be used to save the token of the file, opened with the FilePicker. When you now want to save it again you can retrive the StorageFile by the token and write to it.
Add a FileToken property to your Document class:
public string FileToken { get; set; }
Now when you pick your file you add the file to the FutureAccessList:
...
StorageFile storageFile = await savePicker.PickSaveFileAsync();
if (storageFile != null)
{
CachedFileManager.DeferUpdates(storageFile);
await FileIO.WriteTextAsync(storageFile, Document.Text);
FileUpdateStatus updateStatus = await CachedFileManager.CompleteUpdatesAsync(storageFile);
Document.FileName = savePicker.SuggestedFileName;
Document.IsSaved = true;
//Add the file to the FutureAccessList to get it back later
Document.FileToken = StorageApplicationPermissions.FutureAccessList.Add(storageFile);
}
To retrive the file and save it again:
public async void SaveFile()
{
//Get the file back from the FutureAccessList by its token and write to it
StorageFile file = await StorageApplicationPermissions.FutureAccessList.GetFileAsync(Document.FileToken);
await FileIO.WriteTextAsync(file, Document.Text);
}
Now when you e.g. save your Document class to Json and retrive it after the app restarts you can still use the FileToken to write to the file. There is no need to let the user pick it again using the SaveFilePicker.
When the code above is to complicated or there is no need for this (I don't know what you need this for), you can put a StorageFile propertie directly to your Document class and put the file, that the SaveFilePicker returned in it. But this won't work when restarting the app. The user would always have to pick the file again.

Dotnet controller unable to save gif files

I'm making a converter that receives some image/video and does the process to turn it into a webp file.
With jpg, png and webm files i don't have any problem at all, but for some reason when I attempt to use a gif file I got this error: "Access to the path 'C:\Users\Desktop\computing\api\wwwroot\spin.gif' is denied."
This error occurs when i`m trying to save the file received by a IFormFile.
My controller is like this:
[HttpPost]
[DisableRequestSizeLimit]
public async Task<IActionResult> ConverterToWebp()
{
var webp = new WEBPConverter(new VideoSettings(_videoSettings));
var workingdir = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot");
var (file, _) = GetFile();
if (file == null)
return BadRequest("Arquivo inválido");
var (filepath, _) = await SaveToDir(file, workingdir);
var res = await webp.ConverterWebp(filepath);
if (!res.Success)
return BadRequest(res);
return File(res.bytes, "image/webp");
}
The method GetFile() look like this:
private (IFormFile? file, string? mimetype) GetFile()
{
var files = HttpContext.Request.Form.Files;
var file = files.FirstOrDefault();
if (file == null || file.Length == 0)
return (null, null);
var contentTypeProvider = new FileExtensionContentTypeProvider();
var isBlob = file.FileName.ToLower() == "blob";
var mimetypeParseOk = contentTypeProvider.TryGetContentType(file.FileName, out var mimeType);
if (isBlob)
return (file, "blob");
if (mimetypeParseOk)
return (file, mimeType);
return (null, null);
}
And the method who trigger the error, SaveToDir(), look like this:
private async Task<(string filepath, string filename)> SaveToDir(IFormFile file, string path)
{
var filename = new string(file.FileName
.Replace(' ', '_')
.Normalize(NormalizationForm.FormD)
.Where(ch => char.GetUnicodeCategory(ch) != UnicodeCategory.NonSpacingMark)
.ToArray());
var filepath = Path.Combine(path, filename);
using var stream = new FileStream(filepath, FileMode.Create);
await file.CopyToAsync(stream);
return (filepath, filename);
}
The entire project is using .net core 6.0
If I take one file with .gif extension and change it to .webm I got no error, even though the conversion don`t works great.
I don't know the reason why only if i use gif this method to save in directory don't work and generate that generic error because the path exist and has permissions, and that's why it doesn't trigger error in other files types.

By default IIS does not have permission for the wwwroot folder. You need to grant permissions to the IIS_IUSRS for the folder. I would not recommend this approach as it may be a potential security risk. The approach you could take is:
string path = Path.Combine(Path.GetTempPath(), Path.GetTempFileName());
With this you would save the file to the temp folder and temp file name in the users temp folder, in this case the assigned application user or by default IIS_IUSRS. Don't forget to delete the file after you're done with it.
In the case you want to go with the path of granting the access you do the following:
Go to where your inetpub folder is located
Right click on wwwroot and click on Properties
Switch to the security tab and click Edit...
Look for the IIS_IUSRS user, should be PCNAME\IIS_IUSRS
Select Allow for all permissions.

In the end I managed to solve the problem by saving a file without extesion and using theirs bytes arrays to convert.
But in fact the original question is not solved, any file that I try to use and that has the gif's extension get error. I tried to test changing a webm file that's working with name "test.webm" to "test.gif" and get the same error of permission.
This is how my method got no error:
private async Task<(string filepath, string filename)> SaveToDir(IFormFile file, string path)
{
var timespanEpoch = (int)(DateTime.UtcNow - new DateTime(1970, 1, 1)).TotalSeconds;
var filename = $"web_temp_file-{timespanEpoch}";
var filepath = Path.Combine(path, filename);
using var stream = new FileStream(filepath, FileMode.Create);
await file.CopyToAsync(stream);
return (filepath, filename);
}

Xamarin.Forms - Open file with default app

I need to open a file from storage. I used Launcher.OpenAsync(), but it always tries to open the file in PDF reader. Is there any other way to open a file with default app on Android?
This is the code I have already tried.
private void OpenDocument(string filePath)
{
var localFile = "file://" + filePath;
Launcher.OpenAsync(localFile);
}

string path = "your uri bla-bla-bla";
Launcher.OpenAsync
(new OpenFileRequest()
{
File = new ReadOnlyFile(path)
}
);

UWP, Access to the path is denied

I read some topic about file permission.
Someone said "App can access directories and files which the user manually selected with the FileOpenPicker or FolderPicker"
My codes are like as below:
public async void CsvParse()
{
var picker = new Windows.Storage.Pickers.FileOpenPicker();
picker.FileTypeFilter.Add(".csv");
Windows.Storage.StorageFile file = await picker.PickSingleFileAsync();
if (file != null)
{
string[] lines = File.ReadAllLines(file.Path);//this is where app stops working and gives error message.
}
}
Even when I choose file with FilePicker, it still gives me error. But when I choose file from appx folder, it works fine.
Is there a way to access other locations than app's folder?

try it this way:
public async void CsvParse()
{
var picker = new Windows.Storage.Pickers.FileOpenPicker();
picker.FileTypeFilter.Add(".csv");
Windows.Storage.StorageFile file = await picker.PickSingleFileAsync();
if (file != null)
{
IList<string> lines = await FileIO.ReadLinesAsync(file);//this is where app stops working and gives error message.
}
}
the StorageFile is the way you get access to a file. File.ReadAllLines(file.Path) you are passing a Filename, not the StorageFile but just the filepath is not enough for getting access

how to launch files from sd card in uwp?

I'm trying to create a file explorer for windows 10 mobile
I need to launch files with default app from pathes (not installed directory)
ex. "d:\test.pdf"
Here's what I've tried:
string p = #"a.jpg";
StorageFolder externalDevices = Windows.Storage.KnownFolders.RemovableDevices;
StorageFile file = await externalDevices.GetFileAsync(p);
var success = await Launcher.LaunchFileAsync(fff);

you can use Windows.System.Launcher API to launch the default handler for a file you can read more here
async void DefaultLaunch()
{
// Path to the file in the app package to launch
string imageFile = #"images\test.png";
var file = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFileAsync(imageFile);
if (file != null)
{
// Launch the retrieved file
var success = await Windows.System.Launcher.LaunchFileAsync(file);
if (success)
{
// File launched
}
else
{
// File launch failed
}
}
else
{
// Could not find file
}
}

If you want to access files from SD card, please make sure that you have read the What you can and can't access on the SD card section on document.
Your app can only read and write files of file types that the app has registered to handle in the app manifest file.
Your app can also create and manage folders.
Make sure that you check "Removable Storage" in the capabilities of the appxmanifest.
You must declare a file type association in the Package.appxmanifest in order to read files from the SD card. The following is an example of one that I set up:
Then, I used the following code sample to launch a picture which is contained in "New folder" on SD card successfully.
string p = #"1.jpg";
StorageFolder externalDevices = Windows.Storage.KnownFolders.RemovableDevices;
var rootfolder = (await externalDevices.GetFoldersAsync()).FirstOrDefault();
var folder = await rootfolder.GetFolderAsync("New folder");
var file = await folder.GetFileAsync(p);
var success = await Launcher.LaunchFileAsync(file);