QFileDialog doesn’t list tty* files in /dev/ on Linux

I’m wor开发者_JAVA技巧king on a Linux desktop application that needs to open a USB serial port, typically /dev/ttyUSB0 or /dev/ttyUSB1. I’m using QFileDialog to let the user select the file:

QFileDialog dialog(this);
dialog.setFileMode(QFileDialog::AnyFile);
dialog.setFilter(QDir::System | QDir::AllEntries | QDir::Hidden);
dialog.setViewMode(QFileDialog::Detail);
QStringList fileNames;
if (dialog.exec())
  fileNames = dialog.selectedFiles();

When I direct the FileDialog to /dev, none of the files that I can see by typing “ls /dev -al” are there. The directories show up, but for example, this file doesn’t:

$  ls -al /dev/ttyS0
crw-rw---- 1 root dialout 4, 64 2011-10-09 10:47 /dev/ttyS0

My user is a member of the dialout group:

$ groups
luke adm dialout cdrom audio video plugdev users fuse netdev bluetooth lpadmin admin sambashare

I’ve tried adding QDir::Readable and QDir::Writable and the above file still doesn’t show up. What am I doing wrong?

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It amazes me how often people don't answer the question that was originally asked. I'll try not to do that here, if I can. I've done some homework on this problem since I'm having exactly the same issue. The short answer is that you can't use QFileDialog to reliably list and select nodes in "/dev". When you set the "QDIR::System" bit in the QFileDialog Filter using QFileDialog::setFilter(QDIR::System), you would expect that all the files in /dev would show up, but they do not. Admittedly, there are more entries than when it is not set, but most of the device nodes are still not displayed. It is clear that QFileDialog is doing some additional filtering behind the scenes, and that this filtering cannot be turned off in any obvious way.

On the other hand, if you use the QDir class with the QDir::System filter bit set, then in fact all of the /dev entries do appear in the entryList. For example, assuming that you already have a QComboBox named TTYDevices in your user interface, try something like this:

DevDir=new QDir("/dev","tty*",QDir::Name,QDir::System);
ui->TTyDevices->addItems(DevDir->entryList());

Then use the standard signals from QComboBox to detect and act on selection of the desired device node. By the way, ui is the standard Qt pointer to the instance of your parent window class and should be set up in the Window's constructor. Just make sure that you don't reference it before the constructor calls ui->setupUi(this). If you do, the program will crash.

This trick provides identical functionality to QFileDialog, with the additional features provided by accessing the QDir object directly. It does mean that you cannot easily have the same familiar, uniform interface provided QFileDialog, but it works and is remarkably easy to code.