I've recently transitioned my iOS Unity app to use asset bundles as on demand resources. This all works great! The only problem is that when the application first starts up and all the ODRs are preloaded it just starts to download them from the apple servers. I need to know before preloading them if they require downloading and if so, how big of a download. I need this info to show a prompt for the user to let them know that additional data needs to be downloaded and maybe turn on their wifi etc.

CodePudding user response：

If you are using WWW class then there is this WWW.LoadFromCacheOrDownload, this function takes in a version parameter which you can probably use for checking on versions.

If you are using UnityWebRequest, then maybe you can use the meta files which get generated with asset bundle and then download it and read version or a hash (You will probably have to google a little bit on this what to use) to actually look if you have a version change and do you need to download new version or not.

If none of the above suits you then the hard coded way would be to setup a list of your asset bundles with your versions on a webserver and download it to match it with your local version everytime you start the app.

I hope this atleast helps you look in the correct direction.

CodePudding user response：

I've managed to do this myself in the end. My current setup is the following:

• I have a bunch of assetbundles marked as On Demand Resources.
• When I build the assetbundles I save a file containing the CRC and file sizes of all these bundles and I save it in StreamingAssets to always have it available
• Whenever the app starts up, I try to load the assetbundles from PersistentDataPath against their latest CRC (at first launch there will be no bundles there)
• If any bundles are missing or have invalid CRC, show a prompt to the user that x MB of data needs to be downloaded (taken from the file made at build time)
• After the ODR resources are downloaded, I reencrypt the assetbundle from res:// (the only way I could access it) and move it to PersistentDataPath
• Whenever a new updated comes it, it should contain new CRCs for the changed bundles and the process should restart

It seems to work quite well. The only real issues that I have is that I currently don't know how to delete the downloaded ODR data, and there could be a version mismatch if a user installs the app and defers downloading the extra data, and only opts to do so when an updated version of the app (with different bundle CRCs) is available on the server but they still stay on the older version. This would probabily load the new bundles but will fail the CRC checks for them...