Write to /mnt/extsd

[sconlon]

My Android tablet has a microSD slot which appears in Astro file manager as /mnt/extsd. I have inserted a 16gb card into this and am able to see any files on it again is Atsro. In my app I want to backup a database to this device so I have used:

File.Copy(File.DirRootExternal,"test.db","/mnt/extsd/","test_backup.db")

But I get a error "libcore.io.ErrnoException: open failed: EACCES (Permission denied)"

Earlier in the app I have used DirRootExternal so I believe that should add the necessary permission WRITE_EXTERNAL_STORAGE to the manifest file.

Any suggestions?

Ta.

 

[Erel]

Try to call Log(File.ListFiles("/mnt/extsd/")).

Does it work?

 

[sconlon]

Yes, it works. So I guess reading is not a problem only writing. A permissions issue?

 

[icefairy333]

you should check the permissions of the file system at first

 

[sconlon]

Sorry Erel but how do I do that?

 

[sconlon]

Did you mean to do this within the app or by some other means?

 

[Erel]

You can use File.ExternalWritable to check for write permission to the standard external storage. This however will not work with your storage.

Try to read a file. Does it work?

It seems like there is a permission problem.

 

[sconlon]

Yes, I can read a file from it ok. So how can I change or set write permission on this device. Can it be done within the app or maybe set permanently by some other means? I can write to it on my PC ok so it is not the card itself!

 

[Erel]

Which device are you using?

This link might be related: unable to write files to external sd card - xda-developers

 

[sconlon]

I'm using a Chinese tablet CCP P735 which is ok but has some peculiarities and this could be one of them. However, I looked at the link you gave me and noted the suggestion to 'Add an additional group definition for this permission...<group gid="media_rw" />' I'm not sure how exactly to do this with the Manifest editor - I'm not very familiar with the format of the Manifest file. Can you help?

Ta

 

[Erel]

The solution in this link requires you to edit a system file (this is why it requires root privileges).

 

[sconlon]

Ok. haven't rooted an Android device before but from reading stuff on various forums it seems the process could be different for each tablet and I need to consult with the manufacturer - some hope with that!

 

[RJB]

In a similar vein:

if I try this code in debug mode it works:
/code
File.MakeDir("/mnt/sdcard" , "TestFiles")
Dim TW As TextWriter
TW.Initialize(File.OpenOutput("/mnt/sdcard/TestFiles", "Test.txt", False))
TW.Write(teststring)
TW.Close
/code

The directory is made and the file is written

If I try it in release mode it fails to create the directory and gives the error:
java.io.FileNotFoundException: /mnt/sdcard/TestFiles/Test.txt: open failed: ENOENT (No such file or directory)

or if the directory is there the file write fails.

Any suggestions?
Thanks

 

[Erel]

You should use File.DirRootExternal instead of hardcoding the path. Your current code will not work on all devices.

When the compiler sees a call to File.DirRootExternal (or DirDefaultExternal) it adds the "write storage" permission. This permission is added automatically in debug mode. This is why it fails in release mode.

 

[RJB]

Thanks!