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 CurrentTemplate 21 { 22 get 23 { 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 DataTemplateSelector 2 { 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 try 102 { 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 AysncUnhandledExceptionEventArgs 119 { 120 Exception = exception 121 }; 122 123 UnhandledException(this, exWrapper); 124 125 #if DEBUG && !DISABLE_XAML_GENERATED_BREAK_ON_UNHANDLED_EXCEPTION 126 if (System.Diagnostics.Debugger.IsAttached) System.Diagnostics.Debugger.Break(); 127 #endif 128 return exWrapper.Handled; 129 } 130 131 public event EventHandler<AysncUnhandledExceptionEventArgs> UnhandledException; 132 } 133 134 public class AysncUnhandledExceptionEventArgs : EventArgs 135 { 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 ExceptionHandlingSynchronizationContext 13 .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: " + 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: " + e.Exception.Message) 30 .ShowAsync(); 31 } 32 33 protected override void OnLaunched(LaunchActivatedEventArgs e) 34 { 35 RegisterExceptionHandlingSynchronizationContext(); 36 37 #if DEBUG 38 if (System.Diagnostics.Debugger.IsAttached) 39 { 40 this.DebugSettings.EnableFrameRateCounter = true; 41 } 42 #endif 43 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