The problem is that even if a default image is set, it won't be displayed until one calls setImageUrl(), which in turn will set the source bitmap of the view to null if the url is empty. If the url isn't empty, it makes a request. This means that one is forced to make a network request even if there isn't a valid network url associated with that particular view, otherwise instead of displaying the default image it displays an empty view.

String url = getURL();
    NetworkImageView niv = (NetworkImageView)rootView.findViewById(R.id.niv);
    if(url.length() > 0)
        niv.setImageUrl(url, imageLoader);
    niv.setDefaultImageResId(R.drawable._default);
    niv.setErrorImageResId(R.drawable.error);

需要最新版的 volley,舊版的存在bug,不能設定

可用volley jar 下載地址 http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22com.mcxiaoke.volley%22