在modelview中更改属性并在视图中显示它

Question

我用mvvm模型进行编程。

我有一个文本框（txtResult），它在我的rulesengine中计算并返回到mu modelview。这样可行。 但是我的文本框中没有显示更改。

我的视图的xaml代码（在后台没有任何内容）：

<Window x:Class="RulesEngineExample.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="177" Width="491"
    xmlns:local="clr-namespace:RulesEngineExample" Loaded="Window_Loaded">
<Window.DataContext>
        <local:MainViewModel />
</Window.DataContext>
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="51*" />
        <RowDefinition Height="24*" />
        <RowDefinition Height="28*" />
        <RowDefinition Height="24*" />
        <RowDefinition Height="11*" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="10*" />
        <ColumnDefinition Width="119*" />
        <ColumnDefinition Width="5*" />
        <ColumnDefinition Width="41*" />
        <ColumnDefinition Width="6*" />
        <ColumnDefinition Width="119*" >
        <ColumnDefinition Width="30*" />
        <ColumnDefinition Width="121*" />
        <ColumnDefinition Width="18*" />
    </Grid.ColumnDefinitions>
    <TextBox  Name="txtField1" Text="{Binding Field1, UpdateSourceTrigger=PropertyChanged}"   Grid.Row="1"  Grid.Column="1" />
    <TextBox Name="txtField2" Text="{Binding Field2, UpdateSourceTrigger=PropertyChanged}"  Grid.Row="1"  Grid.Column="5" />
    <TextBox   Name="txtResult" Text="{Binding ResultCalc, Mode=TwoWay,   UpdateSourceTrigger=PropertyChanged}"    Grid.Column="7" Grid.Row="1" IsReadOnly="True" />
    <Label Height="23" Content="="  Grid.Row="1"  Grid.Column="6" />
    <ComboBox  Height="23" SelectedItem="{Binding Operator,  Mode=TwoWay}" Name="cbOperator"  Grid.Row="1" Grid.Column="3">
        <ComboBoxItem Content="+" />
        <ComboBoxItem Content="-" />
        <ComboBoxItem Content="*" />
        <ComboBoxItem Content="/" />
    </ComboBox>
    <Button Content="Regeln bearbeiten" Height="23"  Name="btn"  Grid.Column="7" Grid.Row="3" Click="btn_Click" />
</Grid>
</Window>

并且有我的viewmodel代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;
using System.ComponentModel;
using System.Windows.Media;

namespace RulesEngineExample
{
    public class MainViewModel : ViewModelBase, INotifyPropertyChanged
    {
        public MainViewModel()
        {
            Messenger.Default.Register<double>(this, SetResult);
            Messenger.Default.Register<Brush>(this, SetFailColor);
        }

        private Brush brFailBrush;
        public Brush FailBrush
        {
            get { return brFailBrush; }
            set 
            {
                brFailBrush = value;
                base.RaisePropertyChanged("FailBrush");
            }
        }

        private string strFieldOne;
        public string Field1
        {
            get { return strFieldOne ; }
            set 
            {
                strFieldOne = value;
                OnPropertyChanged("Field1");
            }
        }

        private string strFieldTwo;
        public string Field2
        {
            get { return strFieldTwo; }
            set 
            {
                strFieldTwo = value;
                OnPropertyChanged("Field2");
            }
        }

        private string strResult;
        public string ResultCalc
        {
            get { return strResult; }
            set 
            {
                string strOldResult = strResult ;
                strResult = value;
                base.RaisePropertyChanged("ResultCalc");
                //OnPropertyChangedAtVM("ResultCalc");
            }
        }

        private string strOperator;
        public string Operator
        {
            get { return strOperator;}
            set 
            {
                string[] s = value.Split(':');
                string st = s[s.Length - 1];
                strOperator = st.Trim();
                OnPropertyChanged("Operator");
            }
        }

        public void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
                PropertyChangedItem item = new PropertyChangedItem()
                {
                    Operator = this.Operator,
                    Field1 = this.Field1,
                    Field2 = this.Field2,
                    Result = this.ResultCalc
                };
                Messenger.Default.Send<PropertyChangedItem>(item);
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void SetResult(double dResult)
        {
            this.ResultCalc = dResult.ToString();
            base.RaisePropertyChanged("ResultCalc");
        }

        private void SetFailColor(Brush FailBrush)
        {
            this.FailBrush = FailBrush;
        }
    }
}