Develop Reference

Access a file that was transferred from PC to Android

I want to transfer a file to an Android device using a USB cable and file explorer, and then access it in my Xamarin.Forms app.
As far as I understand there are two ways to do this (and please correct me if I'm wrong):
Since it's an image file - Just put it anywhere and let some
background task find it and add it to what seems to be a virtual
folder of Images. And then access it there.
A more general solution - browse to that specific folder.
Both solutions rely on using FileInfos etc. but unfortunately the folder structure is much different than I see using windows explorer - instead of Alarms, Android, etc. which I see on windows explorer - is see cache, config, etc. using C#, and access to some like data is not allowed (I get an exception). I also tried finding information on how I would search for all images on the device, but either it's not as simple as I thought it would be, or I'm using the wrong keywords.
The file will be put there by a user, so it cannot be added to the project's resources.

Xamarin has a nice way to navigate the files in android, using Android.OS.Environment.ExternalStorageDirectory.Pathwhich you can concatenate with your directory/filename so you can save/access data.
If you want to open the android dialog box so the user can find a file in its device, you can take a look at: https://developer.xamarin.com/recipes/android/data/files/selecting_a_gallery_image/
Remembering that you need to add the READ_EXTERNAL_STORAGE permission to your android manifest file and check runtime permissions. Runtime permissions can be easily checked with https://github.com/jamesmontemagno/PermissionsPlugin

Is it possible for a user to only select file save location once?

I've been trying to learn how to handle saving normal .txt files in UWP, and have realized that it's quite locked down compared to WPF, especially in the sense of what folders you can access without requesting the user to select a location. I have searched for various ways this might be possible but found no working answer.
Question Description:
I basically would love to know if this is possible, and preferably a point in the direction where I can learn how exactly to do this.
Application settings page requires user to select folder where files are saved.
Application remembers this between launches (unsure if this is possible, but I can't require the user to select the folder on every launch)
Application saves files to the specified folder.
In my understanding, this should be possible, as the user is the one specifying the location via filepicker, but is it possible to have this work between launches so that the user wont be required to re-select the save folder?
I need to figure this out, as I would like my application to support selecting attached network drives, cloud storage folders, etc.
Any help is very much appreciated, and if there are any questions I will answer them to the best of my ability.

Fow this purpose there are two access lists designed: FutureAccessList and MostRecentlyUsedList. Once the user has picked up the folder with the picker, you add it to such list and receive a token, which you save for future purpose in LocalSettings:
ApplicationData.Current.LocalSettings.Values["MyFolder"] = StorageApplicationPermissions.FutureAccessList.Add(pickedFolder);
Then later, once you want to access that folder, you can do it like this:
StorageFolder folder = await StorageApplicationPermissions.FutureAccessList.GetFolderAsync(ApplicationData.Current.LocalSettings.Values["MyFolder"].ToString());
You can't save a StorageFolder or a path to it in settings, hence the UWP app needs permissions to access the folder. Using above access lists solves this problem.

I believe you want to save user settings and keep it somewhere so that next time when they launch the application, they can use the same settings.
Please check out this tutorial from Microsoft, which describes how to do exactly that.
https://msdn.microsoft.com/en-us/library/bb397750(v=vs.110).aspx

C# ClickOnce install folder - how windows generate the folder names

I would like to know how Windows generate folder, where will be ClickOnce application installed.
In Startmenu is "shortcut" to file, what is putted in some "startrek" folder like:
C:\Users\USERNAME\AppData\Local\Apps\2.0\GT??4KXX.PRJ\EGV???1G.??C\prin..tion_7???5a2?????74b6_0000.0002_1dae????89111c35
What does those folder names mean?
For example:
If i will have for example some settings.txt file where i want that user can change some parameters of the application. Is there way how to know, WHERE it will be installed and WHERE the file is? (Where user will find this settings.txt file).
I know that i can create the file for example in C:\ and after start the application i will modify the file in "strong" path. But i dont really like too much files, folders, whatever in C:\ and i prefer to have settings files in same folder like the application. But with ClickOnce installations is it really hard - impossible - to find that file.
It seems like when the "startrek" is something like hash of the project.
So i would like to know what does the folder means and if its some hash of the project or what is that.

To find the folder that contains your executable, you can use the Assembly.Location property.
For example:
string exeFolder = System.Reflection.Assembly.GetExecutingAssembly().Location;
However, if you want to store settings for your ClickOnce app, you shouldn't do it by writing a file to the .exe's folder.
Instead, you should use Microsoft's Application Settings support. Doing it any other way is going to be a lot of extra hassle, and Microsoft's support is very good. It does need half an hour to read through the documentation, but it's far and away the best thing to do, IMHO.
(I'm assuming that you only need the settings to be stored on the local PC for the same user to use later. If you want the settings to follow the user around (i.e. roaming settings), you can't use the Microsoft support.)
If you have more complex settings that you want to store in a file that you create directly, you should consider using the isolated storage that the answer from JRoughan mentions.

From inside the ClickOnce app you can find the default directory where files are stored using
ApplicationDeployment.CurrentDeployment.DataDirectory
Or you can use isolated storage and choose whether you want to save per application or per user.
I don't think it's possible to determine these folders from outside the app itself. If you need a known location you'll have to hard-code it.
Update
I also don't believe it's possible to infer what the install directory will be for an app. It would be unwise to use even if possible as updates to the app will not be in the same location.

If you have data that the user is modifying through your program, you will be happier if you don't leave it in the ClickOnce program directory. You can get completely messed up when there's an update. Check out this article about what to do with your data to keep it safe and be able to find it. It talks about putting it in LocalApplicationData, but if you want your user to be able to find it and edit it, just put it in MyDocuments/yourappname/settings or something like that.
I wouldn't use Isolated Storage; there are reported problems with that and ClickOnce.

c#.net application which can opened while opening a folder

I would like to create a c# application which will open when i open a folder automatically.
My c# application is intended to be like a password system, so that the contents in the folder can only viewed after logging in to my application. Everything is ready..........
but i am confused how to open my application directly while opening the folder with a c# script?
I have now created a application which will ask the user for name and password while opening the application and now i want to make it open through the folder to be locked , how to do it?

Ok, first of all if you want the folder to be secure you should encrypt it otherwise all the user has to do to gain access is kill the process.
What i would recommend you do instead is create a encrypted file. For example a zip file. Then all you have to do associate the file with the program and to unpack it with the password. Then when the user is done delete it and overwrite the temporary folder. It's really important that you overwrite it otherwise the encryption is useless.
If you want to avoid conflict with other programs that work with zip files you can make your own file type it does not affect the content of the file in any way.
I hope this helps.

To make sure I understand... you want to build an application that will, when someone tries to open it, will only open after they supply a password. Hmmm... okay. A specific folder, or any folder? Local folders or folders on network shares? I initially was thinking a file system watcher approach, but that will only work on change events, like copying, renaming, deleting, etc. So that won't work. The closest would be to check last accessed time, but that is an alert ex post facto, so this must be rejected. I'm not sure how you could do this in C#. What is wrong with the robust security options MS has already established, like global groups. That provides flexible restrictions on access. Especially over large amounts of folders. Are users going to have one password per folder? Too cumbersome. One password per user? Use Windows authentication to lock it down. How is this app storing the passwords?
I recommend trying to leverage existing technology to solve problems before trying to re-invent the wheel. You have omitted the scope of this, and what you have already attempted, so we may not understand completely.

C# Cannot write to Application.ExecutablePath, some boxes i can some i cannot? uninstall from this

So I have been writing to
Environment.SpecialFolder.ApplicationData
this data file, that upon uninstall needs to be deleted. I am using Innos Setup to build my installer. It works great for me. So my data file hangs out in the above path and I do that cause when I used to try to write it to
Application.ExecutablePath
certain boxes I tested it on would throw a nasty error at me trying to write data there. I do research and somehow its not always writable and its how i came up with the Environment.SpecialFolder.ApplicationData
That is why my data file now resides in the SpecialFolder.ApplicationData. Trouble is if the user uninstalls and reinstalls I need that file gone. It might be a short coming of my knowledge of Innos but I cannot figure out how to know where that file will be to tell innos that.
So then I thought I had a clever solution: Innos can run a file when its done uninstalling, so I had my program create this file "uninstallData.bat" that says:
del "the file in my special folder application data path"
and I wrote it out to drumroll
Application.ExecutablePath
(yes it was a while in development and I had forgot it was't doable.)
So of course I am back to square one, I need to write a file to a path Innos knows about {app} and I need it to be able to delete my data file in the SpecialFolder... i don't care how I do it i just need that file gone.
Are there other Environment. or Application. approches I have missed? Maybe somewhere that is viewable by an uninstaller AND can be written to?
As an aside, I am not sure why my box I develop on can write to the application folder no issue, but it cannot on other boxes... weird.
Any input would be great sorta lost as to how to crack this nut.

The environment location is in the user profile. If there are multiple users on the machine, and they all run the application then a copy of the file will be in each profile.
The path also depends on the OS.
Regardless, the current user's app data location is pointed to by %APPDATA% and %LOCALAPPDATA%. These Windows environment variables should be available within Innos.

Appliccation.ExecutablePath is not writable per standard defintions - the program files folder should never be manipulated by running applications. Ther area number of special folders for that. Nice that you finally found.... what is properly documented by Microsoft for a LONG time now (minimum 10 years).
I suggest you get a proper installer - WIX comes to my mind. Your problem is totally unrelated to C# - it seems to be totally a "crappy installer" issue. Or provide a PROGRAM (not bat file) to run at uninstall. What exatly is your problem there?