用于UWP的MVVMCross可见性值转换器

Question

我正在使用MvvmCross.Plugins.Visibility。

我有“ xmlns：valueConverters =“ using：App.UWP.Converters”

<views:MvxWindowsPage.Resources>
    <valueConverters:VisibilityConverter x:Key="Visibility" />
    <valueConverters:InverseVisibilityConverter x:Key="InvertedVisibility" />
</views:MvxWindowsPage.Resources>

我有以下布局

<Button Content="Log In" Command="{Binding LoginCommand}" Visibility="{Binding IsBusy, Converter{StaticResource InvertedVisibility}}" />
<ProgressRing Visibility="{Binding IsBusy, Converter={StaticResource Visibility}}" />

我的ViewModel具有IsBusy属性

bool _isBusy;
public bool IsBusy
{
    get { return _isBusy; }
    set
    {
        _isBusy = value;
        RaisePropertyChanged(() => IsBusy);
    }
}

当我更改IsBusy属性时，会抛出一个异常，指出“指定的转换无效”。

我需要做什么才能使它正常工作？

编辑堆栈跟踪

   at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e)
  at MvvmCross.Core.ViewModels.MvxNotifyPropertyChanged.<>c__DisplayClass11_0.<RaisePropertyChanged>b__0()
   at MvvmCross.Uwp.Views.MvxWindowsMainThreadDispatcher.RequestMainThreadAction(Action action, Boolean maskExceptions)
   at MvvmCross.Core.ViewModels.MvxNotifyPropertyChanged.RaisePropertyChanged(PropertyChangedEventArgs changedArgs)
   at MvvmCross.Core.ViewModels.MvxNotifyPropertyChanged.RaisePropertyChanged[T](Expression`1 property)
   at intelliSPEC.Core.ViewModels.LoginViewModel.set_IsBusy(Boolean value)
   at intelliSPEC.Core.ViewModels.LoginViewModel.<Login>d__33.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MvvmCross.Core.ViewModels.MvxAsyncCommandBase.<ExecuteConcurrentAsync>d__17.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MvvmCross.Core.ViewModels.MvxAsyncCommandBase.<ExecuteAsync>d__16.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MvvmCross.Core.ViewModels.MvxAsyncCommandBase.<Execute>d__14.MoveNext()
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.<ThrowAsync>b__6_0(Object state)
   at System.Threading.WinRTSynchronizationContext.Invoker.InvokeCore()

Answer 1

我注意到你有一个错字在第一Binding -存在缺失=登录后再Converter 。

但是，我认为主要问题可能是您使用的是MvvmCross转换器而不是本机转换器。 MvvmCross Value Converter是跨平台的解决方案，如果您使用Tibet绑定 ，则可以在所有平台上使用。

但是，如果要使用本机UWP绑定，则必须在转换器周围添加本机Windows包装程序，以便它实现API所需的仅Windows的IValueConverter接口。 为此，请先在您的Core和UWP项目中安装MvvmCross.Plugin.Visibility软件包，然后在UWP项目中的某个位置创建以下类：

public class VisibilityConverter : 
   MvxNativeValueConverter<MvxVisibilityValueConverter> { }
public class InverseVisibilityConverter : 
   MvxNativeValueConverter<MvxInvertedVisibilityValueConverter> { }

我通常将所有这些“本机”类放在一个Converters\\NativeConverters.cs文件中，但这只是一个约定。 您不必为这些类提供任何其他实现。 如果您在绑定中使用转换器，则它将按预期工作。 我已经以这种方式成功运行了您的代码。

还要确保在UWP项目中创建引导类：

public class VisibilityPluginBootstrap
    : MvxPluginBootstrapAction<MvvmCross.Plugins.Visibility.PluginLoader>
{
}