7月29日发布的Windows10正式版,当天安装好以后,在网络不太好的情况下,经过多次尝试终于装上了Visual Studio 2015和Windows 10 10240的SDK.这两周一直在开发UWP,讲讲在其中遇到的一些坑,不定时更新,有兴趣的可以关注下.
1.DataType在UWP中缺失的问题
在WPF中使用过MVVMLight的都知道,我们可以在App.xaml文件中通过DataType将ViewModel和View绑定在一起.
1 <DataTemplate DataType="{x:Type vm:MyViewModel}">2 <views:MyView/>3 </DataTemplate>但是在Windows10(包括WP7等),是没有DataType的属性的,这意味着我们不能用这种方式来实现ViewModel和View的绑定.但是我们可以曲线救国一下,通过key的方式来寻找DataTemplate来绑定.
首先,我们需要改变我们在UWP中的写法.
1 <DataTemplate x:Key="MyViewModel">2 <view:MyView/>3 </DataTemplate>
然后我们在我们的MainPage.xaml文件中加入一个ContentControl.
1 <ContentControl Content="{Binding CurrentViewModel}" ContentTemplate="{Binding Path=CurrentTemplate}" />我们的各个Views是用Usercontrol实现的.我们需要在MainPageViewModel中添加相应的绑定项.
1 public ViewModelBase CurrentViewModel 2 { 3 get 4 { 5 return currentViewModel; 6 } 7 set 8 { 9 if (currentViewModel == value)10 {11 return;12 13 }14 currentViewModel = value;15 RaisePropertyChanged(()=>CurrentViewModel);16 RaisePropertyChanged(()=>CurrentTemplate);17 }18 }19 20 public DataTemplate CurrentTemplate21 {22 get23 {24 if (CurrentViewModel == null)25 {26 return null;27 }28 29 return Untils.DataTemplateSelector.GetTemplate(CurrentViewModel);30 }31 }DataTemplateSelector.GetTemplate是我们整个方法的核心.
1 public static class DataTemplateSelector2 {3 public static DataTemplate GetTemplate(ViewModelBase param)4 {5 Type t = param.GetType();6 return App.Current.Resources[t.Name] as DataTemplate;7 }8 }通过查找Key的方式将ViewModel和View绑定在一起,这样就实现了我们的功能.我们接下来只要关注App.xaml或者相关文件中声明我们的Key就行了.
2.附加属性解决WebView不能直接绑定Html内容的问题
WebView的Source属性只能绑定微软规定的一些地址协议,不能直接绑定HTML的内容.通过附加属性可以解决这个问题,利用的是NavigateToString方法
1 public static readonly DependencyProperty SourceStringProperty = 2 DependencyProperty.RegisterAttached("SourceString", typeof(string), typeof(Untils), new PropertyMetadata("", OnSourceStringChanged)); 3 4 public static string GetSourceString(DependencyObject obj) { return obj.GetValue(SourceStringProperty).ToString(); } 5 public static void SetSourceString(DependencyObject obj, string value) { obj.SetValue(SourceStringProperty, value); } 6 7 private static void OnSourceStringChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) 8 { 9 WebView wv = d as WebView;10 if (wv != null)11 {12 wv.NavigateToString(e.NewValue.ToString());13 }14 }声明一个SourceString的附加属性,然后在变更事件中进行导航,然后Xaml文件中:
1 <WebView Property:Untils.SourceString="{Binding Url,Mode=TwoWay}"/>
这样子,就可以直接绑定Html内容了.
3.异步(async)方法中的异常无法被App的UnhandledException捕获的问题.
这是一个比较严重的问题.目前已知很多的做法就是局部try catch来解决这个问题.这样做是很容易导致Process被强制终止然后引起闪退的问题的.
我这里用了一个线程同步模型类解决这个问题.
1 using System; 2 using System.Threading; 3 using Windows.UI.Xaml.Controls; 4 5 namespace AiJianShu.ExceptionHandler 6 { 7 internal class ExceptionHandlingSynchronizationContext : SynchronizationContext 8 { 9 /// <summary> 10 /// 注册事件. 需要在OnLaunched和OnActivated事件中调用 11 /// </summary> 12 /// <returns></returns> 13 public static ExceptionHandlingSynchronizationContext Register() 14 { 15 var syncContext = Current; 16 if (syncContext == null) 17 throw new InvalidOperationException("Ensure a synchronization context exists before calling this method."); 18 19 20 var customSynchronizationContext = syncContext as ExceptionHandlingSynchronizationContext; 21 22 23 if (customSynchronizationContext == null) 24 { 25 customSynchronizationContext = new ExceptionHandlingSynchronizationContext(syncContext); 26 SetSynchronizationContext(customSynchronizationContext); 27 } 28 29 30 return customSynchronizationContext; 31 } 32 33 /// <summary> 34 /// 将线程的上下文绑定到特定的Frame上面 35 /// </summary> 36 /// <param name="rootFrame"></param> 37 /// <returns></returns> 38 public static ExceptionHandlingSynchronizationContext RegisterForFrame(Frame rootFrame) 39 { 40 if (rootFrame == null) 41 throw new ArgumentNullException("rootFrame"); 42 43 var synchronizationContext = Register(); 44 45 rootFrame.Navigating += (sender, args) => EnsureContext(synchronizationContext); 46 rootFrame.Loaded += (sender, args) => EnsureContext(synchronizationContext); 47 48 return synchronizationContext; 49 } 50 51 private static void EnsureContext(SynchronizationContext context) 52 { 53 if (Current != context) 54 SetSynchronizationContext(context); 55 } 56 57 58 private readonly SynchronizationContext _syncContext; 59 60 61 public ExceptionHandlingSynchronizationContext(SynchronizationContext syncContext) 62 { 63 _syncContext = syncContext; 64 } 65 66 67 public override SynchronizationContext CreateCopy() 68 { 69 return new ExceptionHandlingSynchronizationContext(_syncContext.CreateCopy()); 70 } 71 72 73 public override void OperationCompleted() 74 { 75 _syncContext.OperationCompleted(); 76 } 77 78 79 public override void OperationStarted() 80 { 81 _syncContext.OperationStarted(); 82 } 83 84 85 public override void Post(SendOrPostCallback d, object state) 86 { 87 _syncContext.Post(WrapCallback(d), state); 88 } 89 90 91 public override void Send(SendOrPostCallback d, object state) 92 { 93 _syncContext.Send(d, state); 94 } 95 96 97 private SendOrPostCallback WrapCallback(SendOrPostCallback sendOrPostCallback) 98 { 99 return state =>100 {101 try102 {103 sendOrPostCallback(state);104 }105 catch (Exception ex)106 {107 if (!HandleException(ex))108 throw;109 }110 };111 }112 113 private bool HandleException(Exception exception)114 {115 if (UnhandledException == null)116 return false;117 118 var exWrapper = new AysncUnhandledExceptionEventArgs119 {120 Exception = exception121 };122 123 UnhandledException(this, exWrapper);124 125 #if DEBUG && !DISABLE_XAML_GENERATED_BREAK_ON_UNHANDLED_EXCEPTION126 if (System.Diagnostics.Debugger.IsAttached) System.Diagnostics.Debugger.Break();127 #endif128 return exWrapper.Handled;129 }130 131 public event EventHandler<AysncUnhandledExceptionEventArgs> UnhandledException;132 }133 134 public class AysncUnhandledExceptionEventArgs : EventArgs135 {136 public bool Handled { get; set; }137 public Exception Exception { get; set; }138 }139 }使用实例:
1 public App() 2 { 3 this.InitializeComponent(); 4 this.Suspending += OnSuspending; 5 6 this.UnhandledException += App_UnhandledException; 7 8 } 9 10 private void RegisterExceptionHandlingSynchronizationContext()11 {12 ExceptionHandlingSynchronizationContext13 .Register()14 .UnhandledException += SynchronizationContext_UnhandledException;15 }16 17 private async void App_UnhandledException(object sender, Windows.UI.Xaml.UnhandledExceptionEventArgs e)18 {19 e.Handled = true;20 21 await new MessageDialog("Application Unhandled Exception:\r\n" + e.Exception.Message)22 .ShowAsync();23 }24 25 private async void SynchronizationContext_UnhandledException(object sender, AysncUnhandledExceptionEventArgs e)26 {27 e.Handled = true;28 29 await new MessageDialog("Synchronization Context Unhandled Exception:\r\n" + e.Exception.Message)30 .ShowAsync();31 }32 33 protected override void OnLaunched(LaunchActivatedEventArgs e)34 {35 RegisterExceptionHandlingSynchronizationContext();36 37 #if DEBUG38 if (System.Diagnostics.Debugger.IsAttached)39 {40 this.DebugSettings.EnableFrameRateCounter = true;41 }42 #endif43 44 Frame rootFrame = Window.Current.Content as Frame;45 46 // 不要在窗口已包含内容时重复应用程序初始化，47 // 只需确保窗口处于活动状态48 if (rootFrame == null)49 {50 // 创建要充当导航上下文的框架，并导航到第一页51 rootFrame = new Frame();52 53 rootFrame.NavigationFailed += OnNavigationFailed;54 55 if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)56 {57 //TODO: 从之前挂起的应用程序加载状态58 }59 60 // 将框架放在当前窗口中61 Window.Current.Content = rootFrame;62 }63 64 if (rootFrame.Content == null)65 {66 // 当导航堆栈尚未还原时，导航到第一页，67 // 并通过将所需信息作为导航参数传入来配置68 // 参数69 rootFrame.Navigate(typeof(MainPage), e.Arguments);70 }71 // 确保当前窗口处于活动状态72 Window.Current.Activate();73 }74 75 protected override void OnActivated(IActivatedEventArgs args)76 {77 RegisterExceptionHandlingSynchronizationContext();78 base.OnActivated(args);79 }这样全局的异常就都能在App.xaml.cs文件中被捕获,不会导致闪退.
参考资料:
http://www.codeproject.com/Articles/113152/Applying-Data-Templates-Dynamically-by-Type-in-WP
http://www.markermetro.com/2013/01/technical/handling-unhandled-exceptions-with-asyncawait-on-windows-8-and-windows-phone-8/
https://github.com/kiwidev/WinRTExceptions
原标题：讲讲我在Windows10(uwp)开发中遇到的一些坑.
关键词：Windows
我知道了 