Hi,

We have looked into this issue and it appears that you can not preload a WebView this way. The root of the problem is WPF does not invoke it's internal Measure/Layout/Template logic until the window is visible. We are adding a static WebView.Preload method that can do the preload internally and it should be available in our next build.

Thanks!

public Task Prefetch()
{
var tc = new TaskCompletionSource<bool>();

_webControl.Visibility = Visibility.Hidden;
WebView.Preload((int)WindowSize.Width, (int)WindowSize.Height, "about:blank", (view, args) =>
{
_webControl.WebView = view;
_webView = view;
tc.TrySetResult(true);
return null;
}, null);

return tc.Task;
}

// And here's how I call it.
{
// ...
await _browser.Prefetch();
RefreshContainer(); // this method registers the custom resourcehandlers, exposes .NET functions and set up the webView's JSInitCode, then navigate to the correct URL
}

ContextSwitchDeadlock occured:

Additional information: The CLR has been unable to transition from COM context 0xc3c8b0 to COM context 0xc3c7f8 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations.

// I use this method to start preloading, I know it's a bit of weird that first, I go to about:blank, then I navigate to the actual page, but it would take too much time to rewrite that part
public void Prefetch()
{
_webControl.Visibility = Visibility.Hidden;
WebView.Preload((int)WindowSize.Width, (int)WindowSize.Height, "about:blank", (view, args) =>
{
InitWebView(view); // This method registers custom schemes, exposing .NET functions and setting up JSInitCode
view.LoadUrl(_webView.Url); // after we're ready we're going to the actual page (it needs the exposed .NET functions and the custom scheme, so I figured this is the only way to do it
return null;
}, null);
}

// ...

public override void OnApplyTemplate()
{
base.OnApplyTemplate();
_root = GetTemplateChild("_root") as Grid;
if (_root == null) throw new Exception("There must be a Grid with name: '_root' in Browser ControlTemplate!");

if (_prefetched != null && _prefetched.IsCreated) // The webView is prefetched?
{
_webControl.WebView = _prefetched; // Switch webViews before we put on the WebControl
}

_root.Children.Add(_webControl);
_webControl.Loaded += (sender, args) =>
{
_webControl.Visibility = Visibility.Visible;
};
}

I've run into deadlock using WebView.Preload if I call it more than once (to preload > 1 WebView). First call succeeds. 2nd call never returns the PreloadTask.