QFileWatcher problem

[manjunath369]

Hello,

I am new to QT programming. I am using QFileWatcher in my application and it working fine, but problem is I am getting notifications for all the files and directories including Hidden files and directoris. Is there any way to avoid notifications for hidden files in the phone...?

please can any one help me .....


regards,
Manju

[divanov]

Hello,

I am new to QT programming. I am using QFileWatcher in my application and it working fine, but problem is I am getting notifications for all the files and directories including Hidden files and directoris. Is there any way to avoid notifications for hidden files in the phone...?

please can any one help me .....


regards,
Manju

Do you mean QFileSystemWatcher? To avoid actions on hidden files in the slot attached to fileChanged signal
you can use the following code:

QFileInfo info(fileName);
if (info.isHidden())
    return;

[ltomuta]

Is't it so that fileChanged is triggered only for files I am expressly monitoring? Which means if the file is hidden I should not have it added to the watcher to begin with.

So is this really about avoiding fileChanged or directoryChanged signals for such files?

[lsvensson]

Is't it so that fileChanged is triggered only for files I am expressly monitoring?

If you give a directoy as the path to watch, the QFileSystemWatcher monitors all files in that directory and it's subdirectories. The alternative is to add single files as the watched path.

Which means if the file is hidden I should not have it added to the watcher to begin with.

So is this really about avoiding fileChanged or directoryChanged signals for such files?

Well, the alternative then would be to iterate over all the files in a directory and it's subdirectories and only add the visible files.

I would have thought that it's simpler, though arguably wasteful, to add the whole directory and filter out the hidden files on directoryChanged, like Divanov suggested.

[divanov]

I would have thought that it's simpler, though arguably wasteful, to add the whole directory and filter out the hidden files on directoryChanged, like Divanov suggested.

It depends on number of files and sub-directories and purpose of the monitoring. It's not good to add thousands of watches as well. For example, on Linux you cannot have more than 128 watchers per user with max 8192 instances per watcher (by default).

[manjunath369]

Hi all,

actually i need to watch all the drives in a phone. whenever any changes occur in a file system, i need to get a notification with corresponding file or directory path.

is it possible in QT...?

thanks and regards,
Manju

[lsvensson]

In theory it's possible, just add the root folder path of each drive to your QFileSystemWatcher. However, as divanov mentioned above, the number of files you can monitor in practice may be limited by the system resources.

I can't find anything specific to Symbian about an upper limit of watchers or monitored files, but the Qt documentation mentions that "Some system limits the number of open file descriptors to 256 by default".

Does anyone know of any specifics for Symbian?

[divanov]

In theory it's possible, just add the root folder path of each drive to your QFileSystemWatcher. However, as divanov mentioned above, the number of files you can monitor in practice may be limited by the system resources.

No, you can add one watch to the root folder. The only one watch with several paths is not a problem.

[lsvensson]

The only one watch with several paths is not a problem.

Yes, but there may still be a limit to how many files/paths a single watcher can keep track of. Or is that a misunderstanding on my side?

[divanov]

Yes, but there may still be a limit to how many files/paths a single watcher can keep track of. Or is that a misunderstanding on my side?

Yes, but you have only several disks normally, i.e. ~5 paths only.

[ltomuta]

That depending on what you call "system file". I wouldn't set a watcher on a path like "c:" and then scan the entire file system for a change when directoryChange is signaled.

I think the question for manjunath369 is really what does he want to do? If his interest would be to write an antivirus application for example then surely Qt is not the way to go.