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Николай Михайлов's questions

Martin Hope
Николай Михайлов
Asked: 2024-09-12 02:12:05 +0800 CST
  • 5

假设有一个具有两个属性的 ViewModel，以及处理加载表单和更改文本的命令：

public class MyViewModel : ViewModelBase
{
    public string TestString { get; set; } = "";

    public string TestString2 { get; set; } = "";

    private RelayCommand<RoutedEventArgs> _loadedCommand;

    public RelayCommand<RoutedEventArgs> LoadedCommand =>
        _loadedCommand ??= new RelayCommand<RoutedEventArgs>(Loaded);

    private RelayCommand _textChangedCommand;

    public RelayCommand TextChangedCommand =>
        _textChangedCommand ??= new RelayCommand(TextChanged);


    private void Loaded(RoutedEventArgs e)
    {
        TestString = "Loaded";
    }

    private void TextChanged()
    {
        TestString2 = "Modified";
    }
}

XAML 形式：

<UserControl x:Class="WpfApp.Views.MyView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApp.Views"
             xmlns:viewmodel="clr-namespace:WpfApp.ViewModels"
             xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
             d:DataContext="{d:DesignInstance Type=viewmodel:MyViewModel}"
             mc:Ignorable="d" 
             d:DesignHeight="800" d:DesignWidth="1200">

    <i:Interaction.Triggers>
        <i:EventTrigger EventName="Loaded">
            <i:InvokeCommandAction Command="{Binding LoadedCommand}" PassEventArgsToCommand="True"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>

    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        
        <TextBox Text="{Binding TestString}">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="TextChanged">
                    <i:InvokeCommandAction Command="{Binding TextChangedCommand}"/>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </TextBox>

        <TextBlock Text="{Binding TestString2}" Grid.Column="1"/>
    </Grid>
</UserControl>

TextBlock 应将其文本更改为“已修改”，但这不会发生，因为建立绑定需要太长时间，因此 TextChanged 事件在绑定完成之前发生。

如果添加延迟，则会出现“已修改”字样：

private async void Loaded(RoutedEventArgs e)
{
    await Task.Delay(1000);
    TestString = "Loaded";
}

有没有一个好的方法来解决这个问题？

c#