LiveData remove Observer after first callback

How do I remove the observer after I receive the first result? Below are two code ways I've tried, but they both keep receiving updates even though I have removed the observer.

Observer observer = new Observer<DownloadItem>() {
        @Override
        public void onChanged(@Nullable DownloadItem downloadItem) {
            if(downloadItem!= null) {
                DownloadManager.this.downloadManagerListener.onDownloadManagerFailed(null, "this item already exists");
                return;
            }
            startDownload();
            model.getDownloadByContentId(contentId).removeObservers((AppCompatActivity)context);
        }
    };
    model.getDownloadByContentId(contentId).observeForever(observer);

 model.getDownloadByContentId(contentId).observe((AppCompatActivity)context, downloadItem-> {
             if(downloadItem!= null) {
                this.downloadManagerListener.onDownloadManagerFailed(null, "this item already exists");
                return;
            }
            startDownload();
            model.getDownloadByContentId(contentId).removeObserver(downloadItem-> {});
        } );

Your first one will not work, because observeForever() is not tied to any LifecycleOwner.

Your second one will not work, because you are not passing the existing registered observer to removeObserver().

You first need to settle on whether you are using LiveData with a LifecycleOwner (your activity) or not. My assumption is that you should be using a LifecycleOwner. In that case, use:

Observer observer = new Observer<DownloadItem>() {
    @Override
    public void onChanged(@Nullable DownloadItem downloadItem) {
        if(downloadItem!= null) {
            DownloadManager.this.downloadManagerListener.onDownloadManagerFailed(null, "this item already exists");
            return;
        }
        startDownload();
        model.getDownloadByContentId(contentId).removeObservers((AppCompatActivity)context);
    }
};

model.getDownloadByContentId(contentId).observe((AppCompatActivity)context, observer);