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I'm trying to make one of my QML apps "offline capable" - that means I want users to be able to use the application when not connected to the internet.

The main problem I'm seeing is the fact that I'm pretty much pulling a QML file with the UI from one of my HTTP servers, allowing me to keep the bulk of the code within reach and easily updatable.

My "main QML file" obviously has external dependencies, such as fonts (using FontLoader), images (using Image) and other QML components (using Loader).

AFAIK all those resources are loaded through the Qt networking stack, so I'm wondering what I'll have to do to make all resources available when offline without having to download them all manually to the device.

Is it possible to do this by tweaking existing/implementing my own cache at Qt/C++ level or am I totally on the wrong track?

Thanks!

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    You're pulling the QML file every time the application is started? Commented Mar 29, 2015 at 16:08

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A simple solution is to invert the approach: include baseline files within your application's executable/bundle. Upon first startup, copy them to the application's data directory. Then, whenever you have access to your server, you can update the data directory.

All modifications of the data directory should be atomic - they must either completely succeed, or completely fail, without leaving the data directory in an unusable state.

Typically, you'd create a new, temporary data folder, and copy/hardlink the files there, and download what's needed, and only once everything checks out you'd swap the old data directory with the new one.

Letting your application access QML and similar resources directly online is pretty much impossible to get right, unless you insist on explicitly versioning all the resources and having the version numbers in the url.

Suppose your application was started, and has loaded some resources. There are no guarantees that the user has went to all the QML screens - thus only some resources will be loaded. QML also makes no guarantees as to how often and when will the resources be reloaded: it maintains its own caches, after all. Sometime then you update the contents on the server. The user proceeds to explore more of the application after you've done the changes, but now the application he experiences is a frankenstein of older and newer pieces, with no guarantees that these pieces are still meant to work together. It's a bad idea.

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