访问路径被拒绝（Xamarin / Android）

Question

I am running Windows 10, Visual Studio 2015, and Xamarin. I am rather new to Xamarin (just to set the ground level). I am currently having an issue after I updated recently. My application was working before the update. All my files were read-only, and I had no issues prior the update. Along with that, I have rebuilt the project and I the "clean and rebuild" for the project as well. I have tried it with multiple apps I have, and the other applications do not have this issue. The issue I am getting the following error below.

06-26 13:51:55.108 I/MonoDroid( 6985): UNHANDLED EXCEPTION:
06-26 13:51:55.142 I/MonoDroid( 6985): System.UnauthorizedAccessException: Access to the path "/storage/emulated/0/defaultDirectory/users.ini" is denied.
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.Boolean anonymous, System.IO.FileOptions options) [0x001f1] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.FileStream..ctor (System.String path, System.IO.FileMode mode, System.IO.FileAccess access, System.IO.FileShare share, System.Int32 bufferSize, System.IO.FileOptions options, System.String msgPath, System.Boolean bFromProxy, System.Boolean useLongPath, System.Boolean checkHost) [0x00000] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at (wrapper remoting-invoke-with-check) System.IO.FileStream:.ctor (string,System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare,int,System.IO.FileOptions,string,bool,bool,bool)
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.StreamReader..ctor (System.String path, System.Text.Encoding encoding, System.Boolean detectEncodingFromByteOrderMarks, System.Int32 bufferSize, System.Boolean checkHost) [0x00067] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.StreamReader..ctor (System.String path, System.Text.Encoding encoding, System.Boolean detectEncodingFromByteOrderMarks, System.Int32 bufferSize) [0x00000] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.StreamReader..ctor (System.String path, System.Boolean detectEncodingFromByteOrderMarks) [0x0000d] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.StreamReader..ctor (System.String path) [0x00000] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at (wrapper remoting-invoke-with-check) System.IO.StreamReader:.ctor (string)
06-26 13:51:55.142 I/MonoDroid( 6985):   at System.IO.File.OpenText (System.String path) [0x00000] in <3fd174ff54b146228c505f23cf75ce71>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at QykAndroidApp.AdminLoginActivity.decryptUsers () [0x00033] in <65a7af1659a443738d96e6c2b7534ab2>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at QykAndroidApp.AdminLoginActivity.OnCreate (Android.OS.Bundle savedInstanceState) [0x0008a] in <65a7af1659a443738d96e6c2b7534ab2>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at Android.App.Activity.n_OnCreate_Landroid_os_Bundle_ (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_savedInstanceState) [0x0000f] in <d855bac285f44dda8a0d8510b679b1e2>:0 
06-26 13:51:55.142 I/MonoDroid( 6985):   at (wrapper dynamic-method) System.Object:28564880-3429-412d-9c61-4f5bb9fc103e (intptr,intptr,intptr)
06-26 13:51:55.153 W/art     ( 6985): JNI RegisterNativeMethods: attempt to register 0 native methods for android.runtime.JavaProxyThrowable
An unhandled exception occured.

I've read few articles such as (I posted the Google search for the 3rd item because I read almost everything in the top results). I've tried running the program as an administrator and the directory has open access to anyone.

• Why is access to the path denied?
• System.UnauthorizedAccessException: Access to the path "..." is denied
• https://www.google.com/search?q=RegisterNativeMethods%3A+attempt+to+register+0+native+methods+for+android.runtime.JavaProxyThrowable&oq=RegisterNativeMethods%3A+attempt+to+register+0+native+methods+for+android.runtime.JavaProxyThrowable&aqs=chrome..69i57j69i58.572j0j7&sourceid=chrome&ie=UTF-8

For anyone curious on the code of how I am accessing my file, it is below.

 private List<string> readUsers()
    {
        adminUsers = new List<string>();
        try
        {
            StreamReader readerForFile;

            //create checks for making sure the card is mounted, the directory is found, and the file is found. 
            var filePath = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.Path, "defaultDirectory/users.ini");

            File.SetAttributes(filePath, FileAttributes.Normal);

            if (File.Exists(filePath))
            {
                //Reads enttire document
                //var fillContent = File.ReadAllText(filePath);
                readerForFile = File.OpenText(filePath);
                if (readerForFile == null) { return null; }
                else
                {
                    string line = "";
                    int counter = 0;
                    while ((line = readerForFile.ReadLine()) != null)
                    {
                        adminUsers.Add(line);
                        counter++;
                    }
                }
            }

        }
        catch (IOException e)
        {
            //You'll need to add proper error handling here
            alert.SetMessage("File was not found. " + e).SetNeutralButton("Okay", delegate { QuestionActivity.exit(); }).Create().Show();
        }

        return adminUsers;
    }

Answer 1

You should enable READ_EXTERNAL_STORAGE and WRITE_EXTERNAL_STORAGE permissions in Android. You can follow this blog to enable the permission in runtime https://devblogs.microsoft.com/xamarin/requesting-runtime-permissions-in-android-marshmallow/