windows-phone-8 - 覆盖WP8导航-PhoneApplicationPage中的崩溃

我正在尝试做一个可以说是个坏主意的事情，但我认为这仍然是可能的。我试图覆盖WP8如何处理后退按钮并自己实现。我认为如果我:

计划

只能在整个应用程序中创建一个“框架”和“页面”。

除非自己要退出应用程序，否则请务必自己处理PhoneApplicationPage.BackKeyPress。

再现

Here's a sample project that has the crash

编码

..then它应该工作。但是，我的尝试被Windows Phone阻止了。 Here's the code:

// This basically happens on PhoneApplicationService.OnLaunched
_viewModelChanged.StartWith(ViewModel).Where(x => x != null).Subscribe(vm => {
    var page = default(IViewFor);
    var frame = RootVisual as PhoneApplicationFrame;

    // Find the initial PhoneApplicationPage for the app
    page = RxApp.GetService<IViewFor>("InitialPage");

    // Depending on how we're being signalled (i.e. if this is cold start
    // vs. resume), we need to create the PhoneApplicationFrame ourselves
    if (frame == null) {
        frame = new PhoneApplicationFrame() {
            Content = page,
        };
    }

    page.ViewModel = vm;
    var pg = page as PhoneApplicationPage;
    if (pg != null) {
        pg.BackKeyPress += (o, e) => {
            if (ViewModel.Router.NavigationStack.Count <= 1 ||
                ViewModel.Router.NavigateBack.CanExecute(null)) {
                return;
            }

            e.Cancel = true;
            ViewModel.Router.NavigateBack.Execute(null);
        };
    }

    // Finally, set Application.RootVisual
    RootVisual = frame;
});

悲伤感

这很好用，直到执行此代码后，框架排队的DispatcherItem导致应用程序崩溃:

System.NullReferenceException occurred
Message: A first chance exception of type 'System.NullReferenceException' occurred in Microsoft.Phone.ni.dll
Microsoft.Phone.ni.dll!Microsoft.Phone.Controls.PhoneApplicationPage.InternalOnNavigatedFrom(System.Windows.Navigation.NavigationEventArgs e)   Unknown
Microsoft.Phone.ni.dll!Microsoft.Phone.Controls.PhoneApplicationPage.Microsoft.Phone.Controls.IPhoneApplicationPage.InternalOnNavigatedFromX(System.Windows.Navigation.NavigationEventArgs e)   Unknown
Microsoft.Phone.ni.dll!System.Windows.Navigation.NavigationService.RaiseNavigated(object content, System.Uri uri, System.Windows.Navigation.NavigationMode mode, bool isNavigationInitiator, Microsoft.Phone.Controls.IPhoneApplicationPage existingContentPage, Microsoft.Phone.Controls.IPhoneApplicationPage newContentPage) Unknown
Microsoft.Phone.ni.dll!System.Windows.Navigation.NavigationService.CompleteNavigation(System.Windows.DependencyObject content, System.Windows.Navigation.NavigationMode mode)   Unknown
Microsoft.Phone.ni.dll!System.Windows.Navigation.NavigationService.ContentLoader_BeginLoad_Callback(System.IAsyncResult result) Unknown
Microsoft.Phone.ni.dll!System.Windows.Navigation.PageResourceContentLoader.BeginLoad_OnUIThread(System.AsyncCallback userCallback, System.Windows.Navigation.PageResourceContentLoader.PageResourceContentLoaderAsyncResult result) Unknown
Microsoft.Phone.ni.dll!System.Windows.Navigation.PageResourceContentLoader.BeginLoad.AnonymousMethod__0(object args)    Unknown
[Native to Managed Transition]
mscorlib.ni.dll!System.Delegate.DynamicInvokeImpl(object[] args)    Unknown
System.Windows.ni.dll!System.Windows.Threading.DispatcherOperation.Invoke() Unknown
System.Windows.ni.dll!System.Windows.Threading.Dispatcher.Dispatch(System.Windows.Threading.DispatcherPriority priority)    Unknown
System.Windows.ni.dll!System.Windows.Threading.Dispatcher.OnInvoke(object context)  Unknown
System.Windows.ni.dll!System.Windows.Hosting.CallbackCookie.Invoke(object[] args)   Unknown
System.Windows.RuntimeHost.ni.dll!System.Windows.RuntimeHost.ManagedHost.InvokeDelegate(System.IntPtr pHandle, int nParamCount, System.Windows.Hosting.NativeMethods.ScriptParam* pParams, System.Windows.Hosting.NativeMethods.ScriptParam* pResult)   Unknown

最佳答案

所以，我已经解决了这个问题-我的代码有问题，因为我不了解WP8的工作原理:)这就是我现在所了解的，这可能也是错误的，但是我还是会写它

WP8应用程序的初始化方式:

操作系统通过补水App.xaml.cs创建您的App类

这意味着您的构造函数将运行，在此过程中，您将创建一个PhoneApplicationFrame

创建PhoneApplicationFrame似乎还设置了一个全局静态变量(在App.xaml中创建PhoneApplicationService会发生同样的事情，它会设置PhoneApplicationService.Current)。

NavigationService然后尝试通过资源字符串(即'/MainPage.xaml')重新创建XAML View 。要么重新创建以前被逻辑删除的对象，要么重新创建，否则它默认为WMAppManifest 中的一个(这是我不了解的部分)。

Navigator.Service会调用

PhoneApplicationFrame.Navigated-在这里，您实际上可以开始做一些事情，其中最重要的是设置Application.RootVisual ，它将把Loading ...屏幕发送给

基本上完成所有设置后，

PhoneApplicationService.Launched或PhoneApplicationService.Activated最终会触发，具体取决于如何唤醒您的应用程序。

关于windows-phone-8 - 覆盖WP8导航-PhoneApplicationPage中的崩溃，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/14791060/

wp8

windows-phone-8 - 覆盖WP8导航-PhoneApplicationPage中的崩溃