Script Error: NullReferenceException: downloadhandler.data

Question

Error in the script, at www.downloadHandler.data, Error: NullReferenceException: Object reference not set to an instance of an object

    private IEnumerator LoadBytes(string path, System.Action<byte[]> action) {

        UnityWebRequest www = new UnityWebRequest(path);

        yield return www.SendWebRequest();

        action(www.downloadHandler.data);

    }

Answer 1

Using the constructor of UnityWebRequest creates a generic web request and you would have to set it up completely manually!

Creates a UnityWebRequest with the default options and no attached DownloadHandler or UploadHandler.

Going this way you would need to set it manually

www.downloadHanlder = new DownloadHandlerBuffer();

before starting the request.

---

In general what you rather want to use is UnityWebRequest.Get which already fully configures the UnityWebRequest in order to successfully perform a GET request.

This is somewhat comparable to e.g. using Socket vs TcpClient.

---

Then you should anyway always check if the request was successful at all.

(Also see the example from the API)

private IEnumerator LoadBytes(string path, System.Action<byte[]> action) 
{
    using(var www = UnityWebRequest.Get(path))
    {
        yield return www.SendWebRequest();

        switch (webRequest.result)
        {
            case UnityWebRequest.Result.ConnectionError:
            case UnityWebRequest.Result.DataProcessingError:
                Debug.LogError("Error: " + webRequest.error);
                break;
            case UnityWebRequest.Result.ProtocolError:
                Debug.LogError("HTTP Error: " + webRequest.error);
                break;
            case UnityWebRequest.Result.Success:
                action?.Invoke(www.downloadHandler.data);
                break;
        }
    }
}