readonly 相关问题

我正在尝试以 OneWayToSource 作为模式绑定到 Readonly 属性，但这似乎无法在 XAML 中完成：我正在尝试以 Readonly 作为模式绑定到 OneWayToSource 属性，但似乎无法在 XAML 中完成： <controls:FlagThingy IsModified="{Binding FlagIsModified, ElementName=container, Mode=OneWayToSource}" /> 我得到：无法设置属性“FlagThingy.IsModified”，因为它没有可访问的设置访问器。 IsModified 是 DependencyProperty 上的只读 FlagThingy。我想将该值绑定到容器上的 FlagIsModified 属性。需要明确的是： FlagThingy.IsModified --> container.FlagIsModified ------ READONLY ----- ----- READWRITE -------- 仅使用 XAML 可以吗？更新：好吧，我通过在容器上设置绑定而不是在FlagThingy上修复了这种情况。但我还是想知道这是否可能。 OneWayToSource 的一些研究成果... 选项#1。 // Control definition public partial class FlagThingy : UserControl { public static readonly DependencyProperty IsModifiedProperty = DependencyProperty.Register("IsModified", typeof(bool), typeof(FlagThingy), new PropertyMetadata()); } <controls:FlagThingy x:Name="_flagThingy" /> // Binding Code Binding binding = new Binding(); binding.Path = new PropertyPath("FlagIsModified"); binding.ElementName = "container"; binding.Mode = BindingMode.OneWayToSource; _flagThingy.SetBinding(FlagThingy.IsModifiedProperty, binding); 选项#2 // Control definition public partial class FlagThingy : UserControl { public static readonly DependencyProperty IsModifiedProperty = DependencyProperty.Register("IsModified", typeof(bool), typeof(FlagThingy), new PropertyMetadata()); public bool IsModified { get { return (bool)GetValue(IsModifiedProperty); } set { throw new Exception("An attempt ot modify Read-Only property"); } } } <controls:FlagThingy IsModified="{Binding Path=FlagIsModified, ElementName=container, Mode=OneWayToSource}" /> 选项#3（真正的只读依赖属性） System.ArgumentException：“IsModified”属性无法进行数据绑定。 // Control definition public partial class FlagThingy : UserControl { private static readonly DependencyPropertyKey IsModifiedKey = DependencyProperty.RegisterReadOnly("IsModified", typeof(bool), typeof(FlagThingy), new PropertyMetadata()); public static readonly DependencyProperty IsModifiedProperty = IsModifiedKey.DependencyProperty; } <controls:FlagThingy x:Name="_flagThingy" /> // Binding Code Same binding code... Reflector给出答案： internal static BindingExpression CreateBindingExpression(DependencyObject d, DependencyProperty dp, Binding binding, BindingExpressionBase parent) { FrameworkPropertyMetadata fwMetaData = dp.GetMetadata(d.DependencyObjectType) as FrameworkPropertyMetadata; if (((fwMetaData != null) && !fwMetaData.IsDataBindingAllowed) || dp.ReadOnly) { throw new ArgumentException(System.Windows.SR.Get(System.Windows.SRID.PropertyNotBindable, new object[] { dp.Name }), "dp"); } .... 这是 WPF 的限制，是设计使然。 Connect 上有报道：来自只读依赖属性的 OneWayToSource 绑定我制定了一个解决方案，可以动态地将只读依赖属性推送到名为 PushBinding 的源，我在博客中提到了这里。下面的示例将 OneWayToSource 从只读 DP 的 ActualWidth 和 ActualHeight 绑定到 DataContext 的 Width 和 Height 属性 <TextBlock Name="myTextBlock"> <pb:PushBindingManager.PushBindings> <pb:PushBinding TargetProperty="ActualHeight" Path="Height"/> <pb:PushBinding TargetProperty="ActualWidth" Path="Width"/> </pb:PushBindingManager.PushBindings> </TextBlock> PushBinding 通过使用两个依赖属性（Listener 和 Mirror）来工作。侦听器已绑定 OneWay 到 TargetProperty，并在 PropertyChangedCallback 中更新 Mirror 属性，该属性已绑定 OneWayToSource 到 Binding 中指定的任何内容。可以在这里下载演示项目。它包含源代码和简短的示例用法。写下这个：用途： <TextBox Text="{Binding Text}" p:OneWayToSource.Bind="{p:Paths From={x:Static Validation.HasErrorProperty}, To=SomeDataContextProperty}" /> 代码： using System; using System.Windows; using System.Windows.Data; using System.Windows.Markup; public static class OneWayToSource { public static readonly DependencyProperty BindProperty = DependencyProperty.RegisterAttached( "Bind", typeof(ProxyBinding), typeof(OneWayToSource), new PropertyMetadata(default(Paths), OnBindChanged)); public static void SetBind(this UIElement element, ProxyBinding value) { element.SetValue(BindProperty, value); } [AttachedPropertyBrowsableForChildren(IncludeDescendants = false)] [AttachedPropertyBrowsableForType(typeof(UIElement))] public static ProxyBinding GetBind(this UIElement element) { return (ProxyBinding)element.GetValue(BindProperty); } private static void OnBindChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { ((ProxyBinding)e.OldValue)?.Dispose(); } public class ProxyBinding : DependencyObject, IDisposable { private static readonly DependencyProperty SourceProxyProperty = DependencyProperty.Register( "SourceProxy", typeof(object), typeof(ProxyBinding), new PropertyMetadata(default(object), OnSourceProxyChanged)); private static readonly DependencyProperty TargetProxyProperty = DependencyProperty.Register( "TargetProxy", typeof(object), typeof(ProxyBinding), new PropertyMetadata(default(object))); public ProxyBinding(DependencyObject source, DependencyProperty sourceProperty, string targetProperty) { var sourceBinding = new Binding { Path = new PropertyPath(sourceProperty), Source = source, Mode = BindingMode.OneWay, }; BindingOperations.SetBinding(this, SourceProxyProperty, sourceBinding); var targetBinding = new Binding() { Path = new PropertyPath($"{nameof(FrameworkElement.DataContext)}.{targetProperty}"), Mode = BindingMode.OneWayToSource, Source = source }; BindingOperations.SetBinding(this, TargetProxyProperty, targetBinding); } public void Dispose() { BindingOperations.ClearAllBindings(this); } private static void OnSourceProxyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { d.SetCurrentValue(TargetProxyProperty, e.NewValue); } } } [MarkupExtensionReturnType(typeof(OneWayToSource.ProxyBinding))] public class Paths : MarkupExtension { public DependencyProperty From { get; set; } public string To { get; set; } public override object ProvideValue(IServiceProvider serviceProvider) { var provideValueTarget = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget)); var targetObject = (UIElement)provideValueTarget.TargetObject; return new OneWayToSource.ProxyBinding(targetObject, this.From, this.To); } } 尚未在样式和模板中进行测试，猜测它需要特殊的外壳。这是另一个基于 SizeObserver 的附加属性解决方案，详细信息请参见此处将只读 GUI 属性推回 ViewModel public static class MouseObserver { public static readonly DependencyProperty ObserveProperty = DependencyProperty.RegisterAttached( "Observe", typeof(bool), typeof(MouseObserver), new FrameworkPropertyMetadata(OnObserveChanged)); public static readonly DependencyProperty ObservedMouseOverProperty = DependencyProperty.RegisterAttached( "ObservedMouseOver", typeof(bool), typeof(MouseObserver)); public static bool GetObserve(FrameworkElement frameworkElement) { return (bool)frameworkElement.GetValue(ObserveProperty); } public static void SetObserve(FrameworkElement frameworkElement, bool observe) { frameworkElement.SetValue(ObserveProperty, observe); } public static bool GetObservedMouseOver(FrameworkElement frameworkElement) { return (bool)frameworkElement.GetValue(ObservedMouseOverProperty); } public static void SetObservedMouseOver(FrameworkElement frameworkElement, bool observedMouseOver) { frameworkElement.SetValue(ObservedMouseOverProperty, observedMouseOver); } private static void OnObserveChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e) { var frameworkElement = (FrameworkElement)dependencyObject; if ((bool)e.NewValue) { frameworkElement.MouseEnter += OnFrameworkElementMouseOverChanged; frameworkElement.MouseLeave += OnFrameworkElementMouseOverChanged; UpdateObservedMouseOverForFrameworkElement(frameworkElement); } else { frameworkElement.MouseEnter -= OnFrameworkElementMouseOverChanged; frameworkElement.MouseLeave -= OnFrameworkElementMouseOverChanged; } } private static void OnFrameworkElementMouseOverChanged(object sender, MouseEventArgs e) { UpdateObservedMouseOverForFrameworkElement((FrameworkElement)sender); } private static void UpdateObservedMouseOverForFrameworkElement(FrameworkElement frameworkElement) { frameworkElement.SetCurrentValue(ObservedMouseOverProperty, frameworkElement.IsMouseOver); } } 在控件中声明附加属性 <ListView ItemsSource="{Binding SomeGridItems}" ut:MouseObserver.Observe="True" ut:MouseObserver.ObservedMouseOver="{Binding IsMouseOverGrid, Mode=OneWayToSource}"> 这是绑定到 Validation.HasError 的另一个实现 public static class OneWayToSource { public static readonly DependencyProperty BindingsProperty = DependencyProperty.RegisterAttached( "Bindings", typeof(OneWayToSourceBindings), typeof(OneWayToSource), new PropertyMetadata(default(OneWayToSourceBindings), OnBinidngsChanged)); public static void SetBindings(this FrameworkElement element, OneWayToSourceBindings value) { element.SetValue(BindingsProperty, value); } [AttachedPropertyBrowsableForChildren(IncludeDescendants = false)] [AttachedPropertyBrowsableForType(typeof(FrameworkElement))] public static OneWayToSourceBindings GetBindings(this FrameworkElement element) { return (OneWayToSourceBindings)element.GetValue(BindingsProperty); } private static void OnBinidngsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { ((OneWayToSourceBindings)e.OldValue)?.ClearValue(OneWayToSourceBindings.ElementProperty); ((OneWayToSourceBindings)e.NewValue)?.SetValue(OneWayToSourceBindings.ElementProperty, d); } } public class OneWayToSourceBindings : FrameworkElement { private static readonly PropertyPath DataContextPath = new PropertyPath(nameof(DataContext)); private static readonly PropertyPath HasErrorPath = new PropertyPath($"({typeof(Validation).Name}.{Validation.HasErrorProperty.Name})"); public static readonly DependencyProperty HasErrorProperty = DependencyProperty.Register( nameof(HasError), typeof(bool), typeof(OneWayToSourceBindings), new FrameworkPropertyMetadata(default(bool), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault)); internal static readonly DependencyProperty ElementProperty = DependencyProperty.Register( "Element", typeof(UIElement), typeof(OneWayToSourceBindings), new PropertyMetadata(default(UIElement), OnElementChanged)); private static readonly DependencyProperty HasErrorProxyProperty = DependencyProperty.RegisterAttached( "HasErrorProxy", typeof(bool), typeof(OneWayToSourceBindings), new PropertyMetadata(default(bool), OnHasErrorProxyChanged)); public bool HasError { get { return (bool)this.GetValue(HasErrorProperty); } set { this.SetValue(HasErrorProperty, value); } } private static void OnHasErrorProxyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { d.SetCurrentValue(HasErrorProperty, e.NewValue); } private static void OnElementChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { if (e.NewValue == null) { BindingOperations.ClearBinding(d, DataContextProperty); BindingOperations.ClearBinding(d, HasErrorProxyProperty); } else { var dataContextBinding = new Binding { Path = DataContextPath, Mode = BindingMode.OneWay, Source = e.NewValue }; BindingOperations.SetBinding(d, DataContextProperty, dataContextBinding); var hasErrorBinding = new Binding { Path = HasErrorPath, Mode = BindingMode.OneWay, Source = e.NewValue }; BindingOperations.SetBinding(d, HasErrorProxyProperty, hasErrorBinding); } } } xaml 中的用法 <StackPanel> <TextBox Text="{Binding Value, UpdateSourceTrigger=PropertyChanged}"> <local:OneWayToSource.Bindings> <local:OneWayToSourceBindings HasError="{Binding HasError}" /> </local:OneWayToSource.Bindings> </TextBox> <CheckBox IsChecked="{Binding HasError, Mode=OneWay}" /> </StackPanel> 此实现特定于绑定 Validation.HasError WPF 不会使用 CLR 属性设置器，但似乎它会基于它进行一些奇怪的验证。可能在你的情况下这可能没问题： public bool IsModified { get { return (bool)GetValue(IsModifiedProperty); } set { throw new Exception("An attempt ot modify Read-Only property"); } } 嗯...我不确定我是否同意这些解决方案。如何在属性注册中指定一个忽略外部更改的强制回调？例如，我需要实现一个只读 Position 依赖属性来获取 MediaElement 控件在用户控件内的位置。我是这样做的： public static readonly DependencyProperty PositionProperty = DependencyProperty.Register("Position", typeof(double), typeof(MediaViewer), new FrameworkPropertyMetadata(0d, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault | FrameworkPropertyMetadataOptions.Journal, OnPositionChanged, OnPositionCoerce)); private static void OnPositionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { var ctrl = d as MediaViewer; } private static object OnPositionCoerce(DependencyObject d, object value) { var ctrl = d as MediaViewer; var position = ctrl.MediaRenderer.Position.TotalSeconds; if (ctrl.MediaRenderer.NaturalDuration.HasTimeSpan == false) return 0d; else return Math.Min(position, ctrl.Duration); } public double Position { get { return (double)GetValue(PositionProperty); } set { SetValue(PositionProperty, value); } } 换句话说，只需忽略更改并返回由不具有 public 修饰符的不同成员支持的值。 -- 在上面的例子中，MediaRenderer实际上是私有的MediaElement控件。我解决此限制的方法是在类中仅公开 Binding 属性，将 DependencyProperty 完全保持为私有。我实现了一个“PropertyBindingToSource”只写属性（这个属性不是 DependencyProperty），它可以设置为 xaml 中的绑定值。在此只写属性的设置器中，我调用 BindingOperations.SetBinding 将绑定链接到 DependencyProperty。对于OP的具体示例，它看起来像这样： FlatThingy 实现： public partial class FlatThingy : UserControl { public FlatThingy() { InitializeComponent(); } public Binding IsModifiedBindingToSource { set { if (value?.Mode != BindingMode.OneWayToSource) { throw new InvalidOperationException("IsModifiedBindingToSource must be set to a OneWayToSource binding"); } BindingOperations.SetBinding(this, IsModifiedProperty, value); } } public bool IsModified { get { return (bool)GetValue(IsModifiedProperty); } private set { SetValue(IsModifiedProperty, value); } } private static readonly DependencyProperty IsModifiedProperty = DependencyProperty.Register("IsModified", typeof(bool), typeof(FlatThingy), new PropertyMetadata(false)); private void Button_Click(object sender, RoutedEventArgs e) { IsModified = !IsModified; } } 请注意，静态只读 DependencyProperty 对象是私有的。在控件中，我添加了一个按钮，其单击由 Button_Click 处理。在我的 window.xaml 中使用 FlatThingy 控件： <Window x:Class="ReadOnlyBinding.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:local="clr-namespace:ReadOnlyBinding" mc:Ignorable="d" DataContext="{x:Static local:ViewModel.Instance}" Title="MainWindow" Height="450" Width="800"> <Grid> <Grid.RowDefinitions> <RowDefinition /> <RowDefinition /> </Grid.RowDefinitions> <TextBlock Text="{Binding FlagIsModified}" Grid.Row="0" /> <local:FlatThingy IsModifiedBindingToSource="{Binding FlagIsModified, Mode=OneWayToSource}" Grid.Row="1" /> </Grid> 请注意，我还实现了一个 ViewModel 用于绑定到此处未显示的视图模型。它公开了一个名为“FlagIsModified”的 DependencyProperty，您可以从上面的源代码中收集到。它工作得很好，允许我以松散耦合的方式将信息从 View 推回 ViewModel，并明确定义信息流的方向。您现在的装订方向错误。每当您正在创建的控件上的 IsModified 发生更改时，OneWayToSource 将尝试更新容器上的 FlagIsModified。您想要相反的结果，即将 IsModified 绑定到 container.FlagIsModified。为此，您应该使用绑定模式 OneWay <controls:FlagThingy IsModified="{Binding FlagIsModified, ElementName=container, Mode=OneWay}" /> 枚举成员的完整列表：http://msdn.microsoft.com/en-us/library/system.windows.data.bindingmode.aspx

wpf data-binding xaml readonly

回答 9 投票 0

Python 类函数返回 super()

所以我正在摆弄一个只读可修改的类模式，这在java中很常见。它涉及创建一个包含只读属性的基类，并为修改扩展该类...

python python-3.x design-patterns super readonly

回答 1 投票 0

只读字段和私有 getter 属性之间的区别

我对只读字段和私有 getter 属性之间的区别感到非常困惑。我见过人们在代码中同时使用这两种方法，但我根本不明白是什么让它们有所不同。私人

c# properties field getter readonly

回答 1 投票 0

getter 与只读

以下有什么区别吗？ C级 { // 一：公共静态只读 int ValueAsAMmber = 42; // 二：公共静态 int ValueAsAProperty { 获取 { 返回 42; } } }...