How to load user CSS in a WebKit WebView using PyObjC?

Question

I'd like to have a small browser that uses my own CSS. The problem is that CSS is not loaded or, I guess, it loads but without any effect.

Here is the full code (I don't use an Interface Builder):

import Foundation
import WebKit
import AppKit
import objc

def main():
    app = AppKit.NSApplication.sharedApplication()
    rect = Foundation.NSMakeRect(100,350,600,800)
    win = AppKit.NSWindow.alloc()
    win.initWithContentRect_styleMask_backing_defer_(rect, AppKit.NSTitledWindowMask | AppKit.NSClosableWindowMask | AppKit.NSResizableWindowMask | AppKit.NSMiniaturizableWindowMask, AppKit.NSBackingStoreBuffered, False)
    win.display()
    win.orderFrontRegardless()

    webview = WebKit.WebView.alloc()
    webview.initWithFrame_(rect)

    webview.preferences().setUserStyleSheetEnabled_(objc.YES)
    print webview.preferences().userStyleSheetEnabled()
    cssurl = Foundation.NSURL.URLWithString_("http://dev.stanpol.ru/user.css")
    webview.preferences().setUserStyleSheetLocation_(cssurl)
    print webview.preferences().userStyleSheetLocation()

    pageurl = Foundation.NSURL.URLWithString_("http://dev.stanpol.ru/index.html")
    req = Foundation.NSURLRequest.requestWithURL_(pageurl)
    webview.mainFrame().loadRequest_(req)

    win.setContentView_(webview)
    app.run()

if __name__ == '__main__':
    main()

The code runs without errors. Prints

True
http://dev.stanpol.ru/user.css

but there is no effect of my CSS in the WebView.

I tried different solutions like adding a link to the DOM:

pageurl = Foundation.NSURL.URLWithString_("http://dev.stanpol.ru/index.html")
req = Foundation.NSURLRequest.requestWithURL_(pageurl)
webview.mainFrame().loadRequest_(req)

dom = webview.mainFrame().DOMDocument()
link = dom.createElement_("link")
link.setAttribute_value_("rel", "StyleSheet")
link.setAttribute_value_("type", "text/css")
link.setAttribute_value_("href", "http://dev.stanpol.ru/user.css")

head = dom.getElementsByTagName_(u"head")
hf = head.item_(0)
hf.appendChild_(link)

but in either case it doesn't work.

I don't want to use javascript to load CSS.

Can anybody tell me what's wrong with setting user CSS in my code?

Piffle

Answer 1

Apple doesn't properly document that setUserStyleSheetLocation can only be a local path or data: URL. Qt does explain this in their documentation of the corresponding setting in QtWebKit:

http://doc.qt.nokia.com/latest/qwebsettings.html#setUserStyleSheetUrl

Specifies the location of a user stylesheet to load with every web page.

The location must be either a path on the local filesystem, or a data URL with UTF-8 and Base64 encoded data, such as:

"data:text/css;charset=utf-8;base64,cCB7IGJhY2tncm91bmQtY29sb3I6IHJlZCB9Ow=="

Note: If the base64 data is not valid, the style will not be applied.

Theorize