NavigationProgress 不显示进度条
continue
I'm writing a WPF application using a navigation frame. I'm trying to display a progress-bar while waiting for a page to be loaded.
Like the msdn page sais:
Navigating : Occurs when a new navigation is requested. Can be used to
cancel the navigation.NavigationProgress : Occurs periodically during a download to provide
navigation progress information.Navigated : Occurs when the page has been located and downloaded.
So I have a Grid (navigationStatusGrid) with ProgressBar (navigationProgressBar) and I have a Frame (mainFrame)
These are my event handlers:
private void mainFrame_NavigationProgress(object sender, NavigationProgressEventArgs e)
{
long progress = e.BytesRead * 100 / e.MaxBytes;
Console.WriteLine("Navigating progress:" + progress + "%");
navigationProgressBar.Value = progress;
}
private void mainFrame_Navigating(object sender, NavigatingCancelEventArgs e)
{
Console.WriteLine("start navigating");
mainFrame.Visibility = Visibility.Hidden;
navigationStatusGrid.Visibility= Visibility.Visible;
}
private void mainFrame_Navigated(object sender, NavigationEventArgs e)
{
Console.WriteLine("end navigating");
mainFrame.Visibility = Visibility.Visible;
navigationStatusGrid.Visibility = Visibility.Hidden;
}
This is my output:
start navigating
Navigating progress:4%
Navigating progress:8%
...
Navigating progress:87%
Navigating progress:92%
Navigating progress:96%
Navigating progress:99%
Navigating progress:100%
Navigating progress:100%
end navigating
So you would say it works, but somehow the UI only gets updated when the page is loaded. The UI even freezes up while loading... I don't get to see the progressbar just instantly the loaded page. How do I solve this?
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评论（1）
进度事件对我来说似乎毫无用处，而文档声称导航是同步发生的（如果您使用
Navigate方法），我无法确定它的哪一部分应该是异步的。如果您有一个大型 XAML 会冻结 UI，如果您有一个长时间运行的构造函数也会冻结 UI，并且如果您导航到网页，则进度事件甚至不会被触发。
至少其中一些是有意义的，因为控件是线程相关的，如果在不同线程上异步创建对象会导致问题。如果您有一个长时间运行的构造函数，则需要将工作外部化到本地线程，因为构造函数本身需要在 UI 线程上调用。
The progress event seems rather useless to me, while the documentation claims that the navigation happens assunchronously (if you use the
Navigatemethod) i cannot make out just which part of it is supposed to be assynchronous.If you have a large XAML that will freeze up the UI, if you have a long running contructor that will freeze up the UI as well and if you navigate to a web-page the progress event is not even fired.
At least some of this makes sense as controls are thread-afine, if the object were to be created asynchronously on a different thread that would cause problems. If you have a long running consctructor you need to externalize the work to a thread locally as the constructor itself needs to be called on the UI-thread.