Error m_InstanceID != 0 when downloading texture from the server

Question

I'm getting this error in Unity 5.4 when trying to download the texture from the server.

Here is the code (the link should work):

     UnityWebRequest www = UnityWebRequest.GetTexture("https://0.gravatar.com/avatar/fc2beef90fad49f83d79650a10b5c030?s=256&d=identicon&r=G");
     www.SetRequestHeader("Accept", "image/*");
     async = www.Send();
     while (!async.isDone)
         yield return null;
     if (www.isError) {
         Debug.Log(www.error);
     } else {
         tex = DownloadHandlerTexture.GetContent(www);    // <-------------------
     }

The error looks like this:

m_InstanceID != 0
UnityEngine.Networking.DownloadHandlerTexture:GetContent(UnityWebRequest)

Answer 1

This is a bug. It happens when www.isDone or async.isDone is used with DownloadHandlerTexture.

The work around is to wait for another frame with yield return null; or yield return new WaitForEndOfFrame() before calling DownloadHandlerTexture.GetContent(www);.

UnityWebRequest www = UnityWebRequest.GetTexture("https://0.gravatar.com/avatar/fc2beef90fad49f83d79650a10b5c030?s=256&d=identicon&r=G");
www.SetRequestHeader("Accept", "image/*");
async = www.Send();
while (!async.isDone)
    yield return null;
if (www.isError)
{
    Debug.Log(www.error);
}
else
{
    //yield return null; // This<-------------------
    yield return new WaitForEndOfFrame();  // OR This<-------------------
    tex = DownloadHandlerTexture.GetContent(www);   
}

Although, I don't know how reliable this is. I wouldn't use this in a commercial product unless a thorough test is performed.

A reliable solution is to file for bug about www.isDone, then don't use www.isDone. Use yield return www.Send(); until this is fixed.

UnityWebRequest www = UnityWebRequest.GetTexture("https://0.gravatar.com/avatar/fc2beef90fad49f83d79650a10b5c030?s=256&d=identicon&r=G");
www.SetRequestHeader("Accept", "image/*");
yield return www.Send(); // This<-------------------

if (www.isError)
{
    Debug.Log(www.error);
}
else
{
    tex = DownloadHandlerTexture.GetContent(www);    
}