QML data folder

Question

Im my app based on QML I use Camera and CameraCapture to capture an image from the camera. After it was captured I want to store captured image in application data folder with CameraCapture.captureToLocation(). But I have no idea how to get path to this folder. So my question - how can I get path to application folder wit write permissions? Is there way in Qt to get it? It should be system specified folder, I guess. For example in Android it should be /data/data/AppName. As I see LocalStorage creates its files in some similar place.

Answer 1

You can use QStandardPaths to specify a writable location :

QString path = QStandardPaths::writableLocation(QStandardPaths::GenericDataLocation) ;

Here QStandardPaths::GenericDataLocation returns a directory location where persistent data shared across applications can be stored and it is never empty.

It's also possible use QStandardPaths::ApplicationsLocation or many others which could be found here. You can implement a function in C++ side and use it in your QML to get the standard location.

Answer 2

/data/data/AppName is not mapped in QStandardPaths, but I think it would be better to use this one:

QStandardPaths::AppDataLocation 17 Returns a directory location where persistent application data can be stored. This is an application-specific directory. To obtain a path to store data to be shared with other applications, use QStandardPaths::GenericDataLocation. The returned path is never empty. On the Windows operating system, this returns the roaming path. This enum value was added in Qt 5.4.

or this one in earlier versions:

QStandardPaths::DataLocation 9 Returns the same value as AppLocalDataLocation. This enumeration value is deprecated. Using AppDataLocation is preferable since on Windows, the roaming path is recommended.

These will be set to DataLocation "<APPROOT>/files", "<USER>/<APPNAME>/files" underneath on Android.

But note that from 5.4 on, the latter is deprecated as documented. You can set it then as follows:

QString QStandardPaths::​writableLocation(StandardLocation type)

Returns the directory where files of type should be written to, or an empty string if the location cannot be determined.

Note: The storage location returned can be a directory that does not exist; i.e., it may need to be created by the system or the user.

So, you would write something like this:

QString dataPath = QStandardPaths::​writableLocation(QStandardPaths::AppDataLocation);
// Do not need to check against empty string for this value as per documentatio
CameraCapture.captureToLocation(dataPath);

Note: Please do not use QStandardPaths::ApplicationsLocation for this purpose since that is the non-dedicated location. In addition, it is even unsupported on Android:

ApplicationsLocation not supported (directory not readable)

If you want to share the image across applications, you would need to use this with minor adjustment to the code above. While I think you wanted the one above, it is a bit unclear which one you wanted, so I am mentioning both:

StandardPaths::GenericDataLocation 11 Returns a directory location where persistent data shared across applications can be stored. This is a generic value. The returned path is never empty.

This is set to GenericDataLocation "<USER>" on Android. The exact mappings are mentioned in the class documentation, you just need to scroll down to the tables. I cannot give direct URL as there is no permalink to that section. You can check yourself, too, which fits the best.