Develop Reference

How to track, if the file has changed in the UWP App?

Is there any way to track, if the file I picked using the fileopenpicker changed? I have an UWP APP, which takes data from excel and does sth. with it, but every time I want to take data from the excel file, I have to use file picker again, which makes it useless. Do you know how to automate such task?

You can use FutureAccessList or MostRecnetUsedList to access the file without using the file picker every time.
StorageFile file = await savePicker.PickSaveFileAsync();
if (file != null)
{
// Add to MRU with metadata (For example, a string that represents the date)
string mruToken = Windows.Storage.AccessCache.StorageApplicationPermissions.MostRecentlyUsedList.Add(file, "20120716");
// Add to FA without metadata
string faToken = Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.Add(file);
}
else
{
// The file picker was dismissed with no file selected to save
}
For more info, see this link.

UWP . Copy file from FileOpenPicker to localstorage

FileOpenPicker picker = new FileOpenPicker();
picker.ViewMode = PickerViewMode.Thumbnail;
picker.SuggestedStartLocation = PickerLocationId.ComputerFolder;
picker.FileTypeFilter.Add(".txt");
A user chooses a file to open. How can I store/copy/save that file to localstorage for future use, so every time the app opens, it picks automatically that file?

After the user opens the file using the FileOpenPicker you can "cache" access to it using StorageApplicationPermissions API.
Once you have the StorageFile you want to open automatically, you can "cache" your access to it using the following code:
string token = StorageApplicationPermissions.FutureAccessList.Add( file );
What you get back is a string token, which you can save for example in the app settings. Next time the app is opened, you can retrieve the file again using the following code:
StorageFile file =
await StorageApplicationPermissions.FutureAccessList.GetFileAsync(token);
Note that this API has limitation of at most 1000 items stored, so if you expect that more could be added, you will have to ensure the older files are removed otherwise you would not be able to add new files.
There is also alternative - StorageApplicationPermissions.MostRecentlyUsedList which you can use the same way as the FutureAccessList, but it has the advantage of automatically managing the list. It can store up to 25 items, but it is able to automatically remove the oldest ones when not needed anymore.
Also note, that this APIs can cache access not only to files but also to folders (StorageFolder).
Copying the file to AppData folder
If you just want to create a local copy of the picked file, you can copy it to the local folder of the app.
var file = await picker.PickSingleFileAsync();
if ( file != null )
{
await file.CopyAsync( ApplicationData.Current.LocalFolder );
}

StorageFile file = await openPicker.PickSingleFileAsync();
if (file != null)
{
var yourPath = file.Path;
}
but It won't work as you expect. But remember you can't open file from location you (your app) don't have access to.
edit: yeah, I see in comments that I have missed some part of the qestion ;)
the easiest way to store the information for future re-use would be propably to use LocalSettings
https://msdn.microsoft.com/library/windows/apps/windows.storage.applicationdata.localsettings.aspx
(sorry for the link, but there is no use in copying info from there)

You could:
1) Store the file name in your project settings;
YourNameSpace.Properties.Settings.fileToLoad;
2) write the file name in a local file (look at TextWriter namespace);
3) store the file name in your database if your application is data-driven
... and others.
I am presuming here that you're using WinForms or Console app. If you are using a webForm, you would need to store the file name in a cookie so you could attach the right file to the right user before they log in or give you credenstials. For Webforms, then, look into the use of cookies.

Just to add to the above suggestions, following example from Official Microsoft document shows how to Store file for future access:
var openPicker = new FileOpenPicker();
StorageFile file = await openPicker.PickSingleFileAsync();
// Process picked file
if (file != null)
{
// Store file for future access
Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.Add(file);
}
else
{
// The user didn't pick a file
}

Cannot read any files or directories outside of my application directory

This is really annoying problem and it's going to drive me mad. I like to read information such like files, directories ect. but my app cannot find anything OUTSIDE its folder it runs in.
I'm using Visual Studio 2015 and developing Windows Universal apps.
This routine under works very well if I change the directory inside the folder my app run like "Assets" and any other folder. But outside of my app folder result is zero, not even any errors :-(
Ok, Here is the simple code, What I Do Wrong?
private void GetThem_Click(object sender, RoutedEventArgs e)
{
string myDir = #"c:\mydir\";
string[] files;
files = Directory.GetFiles(myDir,"*.jpg");
foreach (string stuff in files)
{
RESULT.Text = RESULT.Text + stuff + " , ";
}
}

A quick search would have given you the answer : It is not possible to access the file system like a classic desktop app. The answer of #Rico Suter explain you what you can acces and how :
Directories which are declared in the manifest file (e.g. Documents, Pictures, Videos folder)
Directories and files which the user manually selected with the FileOpenPicker or FolderPicker
Files from the FutureAccessList or MostRecentlyUsedList
Files which are opened with a file extension association or via sharing
Once a file is picked by the user, you can add it to MostRecentlyUsedList or FutureAccessList to use it again later using this snippet (C#) from MSDN :
StorageFile file = await savePicker.PickSaveFileAsync();
if (file != null)
{
// Add to MRU with metadata (For example, a string that represents the date)
string mruToken = Windows.Storage.AccessCache.StorageApplicationPermissions.MostRecentlyUsedList.Add(file, "20120716");
// Add to FA without metadata
string faToken = Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.Add(file);
}
Then store the retrieved token because you will need it to access the file using GetFileAsync(token)

Error: "'FileName.docx" has been damaged and can't be opened'" in Windows Phone 8.1

I am trying to open documents but getting error. How do I resolve it?
This is headache for me, Any kind of document is not opening in my application.
I am trying to open PDF file using "PDF Reader" but getting error like this:
"Unable to Open"
Please suggest me.
See my code below.
string file = "test.docx";
IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
if (isf.FileExists(file))
{
isf.DeleteFile(file);
}
var filerun = await ApplicationData.Current.LocalFolder.CreateFileAsync(file);
StorageFolder folder = ApplicationData.Current.LocalFolder;
StorageFile fileopen = await folder.GetFileAsync(file);
await Launcher.LaunchFileAsync(fileopen);

It seems that you are creating a totaly empty file and then try to open it with Word or PDFReader.
On Windows Phone you cannot open with Word an emty file just named filename.docx - try to create on computer a textfile file.txt, rename it to file.docx, copy to your phone, and then open via Files App - it won't work.
File extension only helps to determine the file type, but the most important is what is inside the file.
You should be able to open for example a file created with Word. Here is a sample example how I've done it - add a docx file (created for example on computer with Word) to your solution and change its Build Action to Content. Then try to open it like this:
private async void firstBtn_Click(object sender, RoutedEventArgs e)
{
StorageFolder folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
StorageFile file = await folder.GetFileAsync("sample.docx");
await Launcher.LaunchFileAsync(file);
}
As I've tried - should work without problems. If you encounter some, here is a working sample.
Nothing also stands on your way to prepare some empty docx templates and then inside the app just copy as new files and open them. You may also try to find an API to create Office files.

Windows metro apps - write and read text files in C#?

creating text file:
var myFile = "test";
var folderUsed = Windows.Storage.ApplicationData.Current.LocalFolder;
var fileOption = Windows.Storage.CreationCollisionOption.ReplaceExisting;
var createdFile = await folderUsed.CreateFileAsync(myFile, fileOption);
writing a string into created text file:
var writeThis = "write this ";
await Windows.Storage.FileIO.WriteTextAsync(createdFile, writeThis);
However, it doesn't specify in which part the text file will be created, I'd like to create it inside the package of my app, not in somewhere else in my computer, is it possible?
And secondly, when I execute the second code again, I'd like my file to be written as "write this write this ", not replace the old file and create another one.

You should use
StorageFolder localFolder = ApplicationData.Current.LocalFolder;
since the other folders such as installation folders are restricted and not allowed for read-write operations. Windows Store apps are pretty restricted in this area.
This link is also useful:
http://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh758325.aspx

If your files are in the assets folder then you can access them by:
String path = "ms-appx:///Assets/" + Domain + ".txt";
StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(new Uri(path));
string Value = await FileIO.ReadTextAsync(file);

"However, it doesn't specify in which part the text file will be created, I'd like to create it inside the package of my app, not in somewhere else in my computer, is it possible?"
It's actually 'almost' the only thing possible! your application has explicit access to it's own 'LocalFolder' folder, 'RoamingFolder' location which can be shared between application instances or 'TemporaryFolder' for stuff which gets ditched.
You can save files to thing like pictures library using Windows.Storage.KnownFolders.pictureLibrary if you want, and you can get read only access to your installation folder using 'Windows.ApplicationModel.Package.current.installedLocation' if you so wish.