将UIElement传递给CommandParameter [英] Pass UIElement to CommandParameter

问题描述

我在WPF应用程序中使用MVVM Light.

I'm using MVVM Light in my WPF application.

我创建了一个类RedirectToUriCommandArgument.cs.

public class RedirectToUriCommandArgument : DependencyObject
{
    #region Properties

    public static readonly DependencyProperty PageProperty =
        DependencyProperty.Register(nameof(Page), typeof(object), typeof(RedirectToUriCommandArgument), new UIPropertyMetadata(null));

    public object Page
    {
        get => (object)GetValue(PageProperty);
        set => SetValue(PageProperty, value);
    }

    public string Uri { get; set; }

    #endregion

    #region Methods



    #endregion
}

在.xaml文件中，我使用了:

<Window x:Class="MainClient.Views.AppView"
        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:v="clr-namespace:MainClient.Views"
        xmlns:vm="clr-namespace:MainClient.ViewModel"
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        xmlns:commandArgument="clr-namespace:MainClient.Models.CommandArguments"
        xmlns:local="clr-namespace:MainClient"

        mc:Ignorable="d"
        WindowStartupLocation="CenterScreen"
        Height="350" Width="525">

    <Window.DataContext>
        <vm:AppViewModel x:Name="AppContext"></vm:AppViewModel>
    </Window.DataContext>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="32"/>
        </Grid.RowDefinitions>

        <Frame NavigationUIVisibility="Hidden" x:Name="PageFrame">
            <Frame.Content>
                <Page Name="MainPage"></Page>
            </Frame.Content>
        </Frame>
        <StackPanel Grid.Row="1" Orientation="Horizontal">
            <Button>
                <Button.Content>
                    <TextBlock>Redirect to main view</TextBlock>
                </Button.Content>

                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="Click">
                        <i:InvokeCommandAction Command="{Binding RedirectToViewRelayCommand}">
                            <i:InvokeCommandAction.CommandParameter>
                                <commandArgument:RedirectToUriCommandArgument Page="{Binding ElementName=PageFrame}" Uri="MainView.xaml"></commandArgument:RedirectToUriCommandArgument>
                            </i:InvokeCommandAction.CommandParameter>
                        </i:InvokeCommandAction>
                    </i:EventTrigger>
                </i:Interaction.Triggers>
            </Button>
        </StackPanel>
    </Grid>
</Window>

Page属性始终为空.

我错过了什么吗?

推荐答案

所以我认为问题是，在初始化绑定后，不会创建UIElement(空).之后，不通知绑定，即创建对象.

So I think the problem is, that as binding been initialized the UIElement is not created(null). Afterwords the binding is not notified, that the object is created.

绑定到属性更容易，对象必须实现INotifyPropertyChanged或DependencyObject要注意依赖属性.

Binding to the properties is easyer the object must implement INotifyPropertyChanged or DependencyObject take care about dependency properties.

要解决您的问题，您可以将Binding设置为Delay，例如设置为1000ms，那么它将起作用.这是否是正确的方法值得怀疑.

To solve your issue you could set a Delay for Binding, say to 1000ms, then it will work. It's doubtful whether it is a right way.

<commandArgument:RedirectToUriCommandArgument Page="{Binding ElementName=PageFrame, Delay=1000}" Uri="MainView.xaml"></commandArgument:RedirectToUriCommandArgument>

正确的方法是将绑定源设置为UIElement:

The right way would be just set binding's source to the UIElement:

<commandArgument:RedirectToUriCommandArgument Page="{Binding Source={x:reference PageFrame}}" Uri="MainView.xaml"></commandArgument:RedirectToUriCommandArgument>

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