WKWebKit Mac OS NSPrintOperation

Question

WebKit 1 exposed the WebFrameView where I could call a print operation.

- (void)webView:(WebView *)sender printFrameView:(WebFrameView *)frameView {
  NSPrintOperation *printOperation = [frameView printOperationWithPrintInfo:[NSPrintInfo sharedPrintInfo]];
  [printOperation runOperation];
}

With WKWebKit API I can't seem to figure out how to perform a similar action or which view to grab for printing. All my efforts have come up with blank pages.

Answer 1

Here is marcprux swift solution in Objective C:

    SEL printSelector = NSSelectorFromString(@"_printOperationWithPrintInfo:");
    if ([self.webView respondsToSelector:printSelector]) {
        #pragma clang diagnostic push
        #pragma clang diagnostic ignored "-Warc-performSelector-leaks"
          NSPrintOperation *printOperation = (NSPrintOperation*) [self.webView performSelector:printSelector withObject:[NSPrintInfo sharedPrintInfo]];
        #pragma clang diagnostic pop

        return printOperation;
    }

Answer 2

Amazingly, WKWebView still doesn't support printing on macOS, despite the legacy WebView being deprecated.

Looking at https://github.com/WebKit/webkit/commit/0dfc67a174b79a8a401cf6f60c02150ba27334e5 , printing was implemented years ago as a private API, but for some reason, has not been exposed. If you don't mind using a private API, you can print a WKWebView with:

public extension WKWebView {
    // standard printing doesn't work for WKWebView; see http://www.openradar.me/23649229 and https://bugs.webkit.org/show_bug.cgi?id=151276
    @available(OSX, deprecated: 10.16, message: "WKWebView printing will hopefully get fixed someday – maybe in 10.16?")
    private static let webViewPrintSelector = Selector(("_printOperationWithPrintInfo:")) // https://github.com/WebKit/webkit/commit/0dfc67a174b79a8a401cf6f60c02150ba27334e5


    func webViewPrintOperation(withSettings printSettings: [NSPrintInfo.AttributeKey : Any]) -> NSPrintOperation? {
        guard self.responds(to: Self.webViewPrintSelector) else {
            return nil
        }

        guard let po: NSPrintOperation = self.perform(Self.webViewPrintSelector, with: NSPrintInfo(dictionary: printSettings))?.takeUnretainedValue() as? NSPrintOperation else {
            return nil
        }

        // without initializing the print view's frame we get the breakpoint at AppKitBreakInDebugger:
        // ERROR: The NSPrintOperation view's frame was not initialized properly before knowsPageRange: returned. This will fail in a future release! (WKPrintingView)
        po.view?.frame = self.bounds

        return po
    }
}

You can have this be the default print operation for your NSDocument subclass by adding:

    override func printOperation(withSettings printSettings: [NSPrintInfo.AttributeKey : Any]) throws -> NSPrintOperation {
        return myWebView.webViewPrintOperation(withSettings: printSettings) ?? try super.printOperation(withSettings: printSettings)
    }