c# - WPF 交互命令引用转换器的本地静态资源

Question

我希望创建一个具有行为属性的“可重用”控件项。如所述in this blog

对于数据绑定(bind)，必须转换数据。问题是;作为 StaticResource，它只能看到顶级字典(app)，动态资源不起作用(“只能与依赖属性一起使用”)。

简单(工作)xaml(窗口):

<Window x:Class="testit.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Rectangle x:Name="blah" Fill="Yellow" Stroke="Black" Width="100" Height="100">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseEnter" >
                    <i:InvokeCommandAction Command="{Binding MouseEnterCommand}">
                        <i:InvokeCommandAction.CommandParameter>
                            <Binding Path="Name"
                                     Converter="{StaticResource SelectionConverter}"
                                     RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Rectangle}" />
                        </i:InvokeCommandAction.CommandParameter>
                    </i:InvokeCommandAction>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Rectangle>
        <TextBlock x:Name="namefield" Text="{Binding Data}" HorizontalAlignment="Left" VerticalAlignment="Top"/>
    </Grid>
</Window>

应用:

<Application x:Class="testit.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:testit"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <local:SelectionConverter x:Key="SelectionConverter" />
    </Application.Resources>
</Application>

最后是 View 模型:

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows.Data;

namespace testit
{
    class ViewModel : INotifyPropertyChanged
    {
        private string _data;
        private readonly DelegateCommand<string> _mouseEnterCommand = null;

        public ViewModel() {
            _data = "hello ";
            _mouseEnterCommand = new DelegateCommand<string>(
                (s) => {
                    var a = s ?? "world ";
                    Data += s;
                    return;
                });
        }

        public DelegateCommand<string> MouseEnterCommand => _mouseEnterCommand;

        public string Data {
            get { return _data; }
            set {
                if (value == _data) return;
                _data = value;
                OnPropertyChanged("Data");
            }
        }


        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName) {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
    public class SelectionConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
            if (value == null) return "";
            char[] charArray = ((string)value).ToCharArray();
            Array.Reverse(charArray);
            return new string(charArray);
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
            throw new NotImplementedException();
        }
    }
}

现在如前所述，这“有效”。但是它并没有按照我的意愿行事:它使顶级资源字典变得困惑。我想从应用程序中删除资源。并将其放在网格下。 (或者我使用的任何面板)。

<Grid.Resources>
    <local:SelectionConverter x:Key="SelectionConverter" />
</Grid.Resources>

---

编辑:如果我将上面的行添加到窗口内的网格中，编译时会抛出以下错误(行和位置引用 Converter="{StaticResource SelectionConverter}")

"'Provide value on 'System.Windows.StaticResourceExtension' threw an exception.' Line number '13' and line position '38'."

内部异常:

Cannot find resource named 'SelectionConverter'. Resource names are case sensitive.

为清楚起见，这是修改后的 window.xaml:

<Window x:Class="testit.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        xmlns:local="clr-namespace:testit"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Rectangle x:Name="blah" Fill="Yellow" Stroke="Black" Width="100" Height="100">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="MouseEnter" >
                    <i:InvokeCommandAction Command="{Binding MouseEnterCommand}">
                        <i:InvokeCommandAction.CommandParameter>
                            <Binding Path="Name"
                                     Converter="{StaticResource SelectionConverter}"
                                     RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Rectangle}" />
                        </i:InvokeCommandAction.CommandParameter>
                    </i:InvokeCommandAction>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Rectangle>
        <TextBlock x:Name="namefield" Text="{Binding Data}" HorizontalAlignment="Left" VerticalAlignment="Top"/>
        <Grid.Resources>
            <local:SelectionConverter x:Key="SelectionConverter" />
        </Grid.Resources>
    </Grid>
</Window>

Answer 1

当调用 ProvideValue 时，StaticResource 标记扩展会立即解析资源:

Lookup behavior for that resource is analogous to load-time lookup, which will look for resources that were previously loaded from the markup of the current XAML page

如果 Grid.Resources 是在 Grid 的内容之后定义的，那么当内容Grid 被解析。

因此，将资源放在网格的顶部，以便在使用之前定义其中的任何内容:

<Grid>
    <Grid.Resources>
        <local:SelectionConverter x:Key="SelectionConverter" />
    </Grid.Resources>

    <Rectangle x:Name="blah" Fill="Yellow" Stroke="Black" Width="100" Height="100">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="MouseEnter" >
                <i:InvokeCommandAction Command="{Binding MouseEnterCommand}">
                    <i:InvokeCommandAction.CommandParameter>
                        <Binding Path="Name"
                                 Converter="{StaticResource SelectionConverter}"
                                 RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=Rectangle}" />
                    </i:InvokeCommandAction.CommandParameter>
                </i:InvokeCommandAction>
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </Rectangle>
    <TextBlock x:Name="namefield" Text="{Binding Data}" HorizontalAlignment="Left" VerticalAlignment="Top"/>
</Grid>

如果您能够使用 DynamicResource，您会很好，但当然您不能，因为您发现的原因。