Write Downloaded AssetBundle to Local Storage

Not a good idea: Unity do it for you and store assetbundles in a cache location.

use: WWW.LoadFromCacheOrDownload (url, version)

You MUST maintains a bundle version. For instance you add in your ftp a text file with the version number of your assetBundles. When you update an assetbundle and save it on your ftp, then increase your assetbundle version in those text file.

When you use LoadFromCacheOrDownload then you replace version parameter by yours. And unity will donwload it if version is greater than the last downloaded.

In this way you do not have to deal with copy in a particular folder.

Look at this unity doc: http://docs.unity3d.com/Manual/keepingtrackofloadedassetbundles.html

You will find a AssetBundleManager sample code. I use it.

You can use System.IO.File.WriteAllBytes()

 using System.IO;
 (...)
 public string url = "myweb.com/myAsset";
 public string saveTo = "/folder/myAsset";
 public bool alreadyDownloaded = false;
 IEnumerator SaveAndDownload(){
 WWW www = new WWW(url)
 yield return www;
 byte[] bytes = www.bytes;
 File.WriteAllBytes(saveTo,bytes);
 }

and you're ready

And what's about a dlc ? If the user cleans the cache or if the cache is too small to store the asset bundle ? If the user doesn't know how to cleans the cache ?

I'm looking for the same idea : put my assetbundle on a webserver and then my application can download it and copy inside the internal memory of my device.

Well I put my code here, it works perfectly on my pc but on Android I always got the same and boring error "Asset Bundle header is too small". Indeed the file is created internally but it isn't filled with the data.

I've been looking for many problems and solutions : - Version of Android : Kitkat 4.4 prohibits writing, so I have upgraded my version - Assetbundle which is compressed while AssetBundle.CreateFromFile needs an uncompressed assetbundle, so I have made an uncompressed bundle - Assetbundle is different according to platforms, so I have made an assetbundle for Android (+uncompressed as well) - And now I'm looking for C# managed array (byte array here) can't be interpreted by Android ?

Here is the code :

 public GameObject cible;
     public Scrollbar progressbar;
     public Text displayedtext;
     public GameObject progress;
 
     static WWW objSERVER;
     static string pathURL;
     static string pathLOCAL;
 
     //IEnumerator allows yield so the information is not accessed
     //before it finished downloading
     IEnumerator Start () 
     {
         pathURL = "www.mywebsite.net/file"; //location of the file on the server
         pathLOCAL = Application.persistentDataPath + "/../assetbundles/"+"test" +".unity3d"; //location of the file on the device
 
         objSERVER = new WWW(pathURL);
 
         // Wait for download to finish
         yield return objSERVER;
 
         // Save it to disk
         SaveDownloadedAsset(objSERVER); 
         Debug.Log ("------------------- HERE THE PATH -------------------" + "\n" + Application.persistentDataPath);
         AssetBundle objLOCAL = AssetBundle.CreateFromFile (pathLOCAL);
         yield return objLOCAL;
 
         // Instantiate the asset bundle
         GameObject Model3D = Instantiate (objLOCAL.mainAsset) as GameObject;
 
         // Parenting
         Model3D.transform.parent = cible.transform;
 
         // Positioning
         Model3D.transform.localPosition = new Vector3 (0.62f, -0.98f, 0.94f);
 
         // Resize it
         Model3D.transform.localScale = new Vector3 (0.10f, 0.10f, 0.10f);
 
         objLOCAL.Unload (false);
     }
 
     public void SaveDownloadedAsset(WWW objSERVER) 
     {
         // Create the directory if it doesn't already exist
         if (!Directory.Exists(Application.persistentDataPath + "/../assetbundles/"))
         {
             Directory.CreateDirectory(Application.persistentDataPath + "/../assetbundles/");
         }
 
         // Initialize the byte string
         byte[] bytes = objSERVER.bytes;
 
         // Creates a new file, writes the specified byte array to the file, and then closes the file. 
         // If the target file already exists, it is overwritten.
         File.WriteAllBytes(pathLOCAL, bytes);
     }
 }