private void OnNavigationFailed(NavigationFailedEventArgs e)
{
NavigationFailed?.Invoke(this, e);
}
private void Navigate(Uri oldValue, Uri newValue, NavigationType navigationType)
{
Debug.WriteLine("Navigating from '{0}' to '{1}'", oldValue, newValue);
// set IsLoadingContent state
SetValue(IsLoadingContentPropertyKey, true);
// cancel previous load content task (if any)
// note: no need for thread synchronization, this code always executes on the UI thread
if (_tokenSource != null) {
_tokenSource.Cancel();
_tokenSource = null;
}
// push previous source onto the history stack (only for new navigation types)
if (oldValue != null && navigationType == NavigationType.New) {
_history.Push(oldValue);
}
object newContent = null;
if (newValue != null) {
// content is cached on uri without fragment
var newValueNoFragment = NavigationHelper.RemoveFragment(newValue);
if (navigationType == NavigationType.Refresh || !_contentCache.TryGetValue(newValueNoFragment, out newContent)) {
var localTokenSource = new CancellationTokenSource();
_tokenSource = localTokenSource;
// load the content (asynchronous!)
var scheduler = TaskScheduler.FromCurrentSynchronizationContext();
var task = ContentLoader.LoadContentAsync(newValue, _tokenSource.Token);
task.ContinueWith(t => {
try {
if (t.IsCanceled || localTokenSource.IsCancellationRequested) {
Debug.WriteLine("Cancelled navigation to '{0}'", newValue);
}
else if (t.IsFaulted) {
// raise failed event
var failedArgs = new NavigationFailedEventArgs {
Frame = this,
Source = newValue,
Error = t.Exception?.InnerException,
Handled = false
};
OnNavigationFailed(failedArgs);
// if not handled, show error as content
newContent = failedArgs.Handled ? null : failedArgs.Error;
SetContent(newValue, navigationType, newContent, true);
}
else {
newContent = t.Result;
if (ShouldKeepContentAlive(newContent)) {
// keep the new content in memory
_contentCache[newValueNoFragment] = newContent;
}
SetContent(newValue, navigationType, newContent, false);
}
}
finally {
// clear global tokenSource to avoid a Cancel on a disposed object
if (_tokenSource == localTokenSource) {
_tokenSource = null;
}
// and dispose of the local tokensource
localTokenSource.Dispose();
}
}, scheduler);
return;
}
}
// newValue is null or newContent was found in the cache
SetContent(newValue, navigationType, newContent, false);
}
