WPF : MVVM Microsoft.Expression.Interaction

Question

我正在研究MVVM，我使用了交互。

​

目的是在文本框中输入任何内容，在TextBlock中也会显示同样的内容。

交互触发器将完成文本框的事件PreviewTextInput。

但它带来了错误，但并不像预期的那样起作用。

已附加了运行时映像中的绑定错误。

下面是密码。

XAML

<Window x:Class="MVVMApp.TextBindings"
    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:MVVMApp"
    xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
    mc:Ignorable="d"
    
    Title="Text Bindings" Height="450" Width="800">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="100"></RowDefinition>
        <RowDefinition Height="100"></RowDefinition>
        <RowDefinition Height="100"></RowDefinition>
        <RowDefinition Height="100"></RowDefinition>
        <RowDefinition Height="100"></RowDefinition>
        <RowDefinition Height="100"></RowDefinition>
        <RowDefinition Height="100"></RowDefinition>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="200"></ColumnDefinition>
        <ColumnDefinition Width="200"></ColumnDefinition>
        <ColumnDefinition Width="200"></ColumnDefinition>
        <ColumnDefinition Width="200"></ColumnDefinition>
    </Grid.ColumnDefinitions>
    <TextBlock Text="Enter Text Value" Grid.Row="0" Grid.Column="0"/>
    <TextBox Name="txtBox1" Text="{Binding BxVal,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Grid.Row="0" Grid.Column="1" Width="150" Height="30">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="PreviewTextInput">
                <i:InvokeCommandAction Command="{Binding cmdType}" CommandParameter="{Binding BxVal,ElementName=txtBox1}"></i:InvokeCommandAction>
            </i:EventTrigger>
            </i:Interaction.Triggers>
    </TextBox>
    <TextBlock Text="Result --> " Grid.Row="1" Grid.Column="0"/>
    <TextBlock  Text="{Binding Result,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Background="Lavender" Grid.Row="1" Grid.Column="1"/>
</Grid>

MVVM

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MVVMApp.Helper;
namespace MVVMApp.ViewModel
{
class TextBindingsVM :ViewModelBase
 {
    
    DelegateCommand <object> cmdType { get; set; }
    
    private string _Result { get; set; }
    public string Result
    {
        get { return _Result; }
        set
        {
              _Result = value;
               OnPropertyChanged(this, "Result");
        }
    }
    private string _BxVal { get; set; }

    public string BxVal
    {
        get { return _BxVal; }
        set
        {
            _BxVal = value;
            OnPropertyChanged(this, "BxVal");
            Result = BxVal;
        }
    }

    public TextBindingsVM()
    {
        cmdType = new DelegateCommand<object>(cmdType_Execute);
    }

    private void cmdType_Execute(object obj)
    {
        throw new NotImplementedException();
    }
}

}

Answer 1

我发现了问题。实际上，INotifyPropertyChanged没有在ViewModelBase类中实现。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MVVMApp.Helper
{
    class ViewModelBase:INotifyPropertyChanged
    {

        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged(object sender, string PropertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
            }
        }
    }
}