c# - 在ViewModel中修改后，String属性在View中不会更新

Question

我有一个WPF窗口，其中显示基于一系列日期的事件列表。我还有一个字符串属性，如果用户选择了错误的日期范围，我想在其中显示错误消息。 (“开始”日期大于“结束”日期。)

在更改日期控制值时，我启动了一个命令以刷新数据网格中的事件。在此之前，我确认日期范围是有效的。如果没有，我会在标签中显示错误消息。

问题是，即使ViewModel将属性设置为错误消息的文本，View也不会使用相应的值进行更新。

我在这里做错了什么？

这是我的代码的一些示例。

<UserControl
         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:prism="http://prismlibrary.com/"             
         xmlns:igDP="http://infragistics.com/DataPresenter" 
         xmlns:igEditors="http://infragistics.com/Editors" 
         x:Class="ADM.Module.Event.Views.EventLogView"             
         prism:ViewModelLocator.AutoWireViewModel="True">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="50"/>
        <RowDefinition Height="25"/>
        <RowDefinition Height="25"/>
        <RowDefinition />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition  Width="120"/>
        <ColumnDefinition  Width="140"/>
        <ColumnDefinition  Width="30"/>
        <ColumnDefinition  Width="140"/>
        <ColumnDefinition />
    </Grid.ColumnDefinitions>

    <Label Content="{Binding Header, Mode=OneTime}" FontSize="25" FontWeight="Bold" Grid.ColumnSpan="5"/>

    <Label Content="Select a date range : " Grid.Row="1" />

    <igEditors:XamDateTimeEditor HorizontalAlignment="Left"  Margin="2,2,2,2" Grid.Row="1" Grid.Column="1" VerticalAlignment="Top"
                                 Format="yyyy-MM-dd HH:mm:ss" Mask="yyyy-mm-dd hh:mm:ss" Value="{Binding DateFrom}" Theme="Office2010Blue" >
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="ValueChanged">
                <i:InvokeCommandAction Command="{Binding RefreshEventLogCommand}" />
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </igEditors:XamDateTimeEditor>

    <Label Content=" to " Grid.Row="1" Grid.Column="2" />

    <igEditors:XamDateTimeEditor  HorizontalAlignment="Left"  Margin="2,2,2,2" Grid.Row="1" Grid.Column="3" VerticalAlignment="Top"
                                  Format="yyyy-MM-dd HH:mm:ss" Mask="yyyy-mm-dd hh:mm:ss" Value="{Binding DateTo}" Theme="Office2010Blue" >
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="ValueChanged">
                <i:InvokeCommandAction Command="{Binding RefreshEventLogCommand}" />
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </igEditors:XamDateTimeEditor>

    <Label Content="{Binding DateRangeError}" Foreground="Red" Grid.Row="2" Grid.ColumnSpan="5" />

    <igDP:XamDataGrid HorizontalAlignment="Stretch" Margin="2,2,2,2" Grid.Row="3" Grid.ColumnSpan="5" VerticalAlignment="Stretch"
                        DataSource="{Binding EventLogRecords}" Theme="Office2010Blue">

        <igDP:XamDataGrid.FieldLayoutSettings>
            <igDP:FieldLayoutSettings AllowDelete="False" HighlightAlternateRecords="True" AllowAddNew="False" AutoArrangeCells="LeftToRight"  
                                      ResizingMode="Immediate" SelectionTypeRecord="Single" AutoGenerateFields="False" />

        </igDP:XamDataGrid.FieldLayoutSettings>

        <igDP:XamDataGrid.FieldSettings>
            <igDP:FieldSettings AllowRecordFiltering="True" />
        </igDP:XamDataGrid.FieldSettings>

        <igDP:XamDataGrid.FieldLayouts>
            <igDP:FieldLayout>
                <igDP:FieldLayout.Fields>

                    <igDP:Field Name="EventDate" Label="Date" AllowEdit="False" Format="yyyy-MM-dd H:mm:ss" >
                        <igDP:Field.Settings>
                            <igDP:FieldSettings AllowRecordFiltering="False" />
                        </igDP:Field.Settings>
                    </igDP:Field>
                    <igDP:UnboundField Name="Severities" Label="Severity" BindingPath="Severities.SeverityText" AllowEdit="False" />
                    <igDP:UnboundField Name="LogTypes" Label="Type" BindingPath="LogTypes.LogTypeName" AllowEdit="False" />
                    <igDP:Field Name="EventMsg" Label="Message" AllowEdit="False"  >
                        <igDP:Field.Settings>
                            <igDP:FieldSettings FilterOperandUIType="TextBox" FilterOperatorDefaultValue="Contains" />
                        </igDP:Field.Settings>
                    </igDP:Field>

                </igDP:FieldLayout.Fields>
            </igDP:FieldLayout>
        </igDP:XamDataGrid.FieldLayouts>
    </igDP:XamDataGrid>

</Grid>

using Prism.Commands;
using ADM.DataModel;
using ADM.Infrastructure.BaseClass;
using ADM.Module.Event.Models;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace ADM.Module.Event.ViewModels
{
    public class EventLogViewModel : TabViewModelBase, IEventLogViewModel
    {
        private EventLogModel _model;
        public EventLogViewModel()
        {
            Header = "Event Log";

            var now = DateTime.Now;
            DateFrom = new DateTime(now.Year, now.Month, now.Day, 0, 0, 0);
            DateTo = new DateTime(now.Year, now.Month, now.Day, 23, 59, 59);

            _model = new EventLogModel();
            EventLogRecords = _model.GetEventLogsByDate(DateFrom, DateTo);

            RefreshEventLogCommand = new DelegateCommand(RefreshEventLog);
        }

        #region Properties
        private DateTime _dateFrom;
        public DateTime DateFrom
        {
            get { return _dateFrom; }
            set
            {
                _dateFrom = value;
                SetProperty(ref _dateFrom, value);
            }
        }

        private DateTime _dateTo;
        public DateTime DateTo
        {
            get { return _dateTo; }
            set
            {
                _dateTo = value;
                SetProperty(ref _dateTo, value);
            }
        }

        private string _dateRangeError;
        public string DateRangeError
        {
            get { return _dateRangeError; }
            set
            {
                _dateRangeError = value;
                SetProperty(ref _dateRangeError, value);
            }
        }

        private ObservableCollection<EventLogs> _eventLogRecords;
        public ObservableCollection<EventLogs> EventLogRecords
        {
            get {
                return _eventLogRecords;
            }
            private set {
                _eventLogRecords = value;
                SetProperty(ref _eventLogRecords, value);
            }

        }
        #endregion Properties

        #region Commands
        public ICommand RefreshEventLogCommand { get; private set; }

        public void RefreshEventLog()
        {
            if (ValidateDateRange(DateFrom, DateTo))
            {
                EventLogRecords.Clear();
                EventLogRecords.AddRange(_model.GetEventLogsByDate(DateFrom, DateTo));
            }
        }

        private bool ValidateDateRange(DateTime fromDate, DateTime toDate)
        {
            if (DateFrom > DateTo)
            {
                DateRangeError = "The From Date need to be set to before the To Date.";
                return false;
            }

            return true;
        }

        #endregion Commands
    }
}


using Prism;
using Prism.Mvvm;
using ADM.Infrastructure.DockManager;
using System;

namespace ADM.Infrastructure.BaseClass
{
    public class TabViewModelBase : BindableBase, IActiveAware, IDockAware
    {
        public TabViewModelBase()
        {
        }

        #region IActiveAware

        bool _isActive;
        public bool IsActive
        {
            get { return _isActive; }
            set
            {
                _isActive = value;
                SetProperty(ref _isActive, value);
            }
        }

        public event EventHandler IsActiveChanged;

        #endregion //IActiveAware

        #region IDockAware

        private string _header;
        public string Header
        {
            get { return _header; }
            set
            {
                _header = value;
                SetProperty(ref _header, value);
            }
        }

        #endregion //IDockAware
    }
}

Answer 1

首先，您要设置属性的背景两次。手动一次，然后再次使用SetProperty。 SetProperty实际上检查值是否相同，因为它们将不会设置属性或调用INPC。因此，您实质上是在设置它，然后尝试再次设置它，这不会发生。

您的媒体资源应按以下方式定义:

    private string _dateRangeError;
    public string DateRangeError
    {
        get { return _dateRangeError; }
        set { SetProperty(ref _dateRangeError, value); }
    }

然后，您会遇到错误消息相同的问题。因此，将永远不会调用INPC，因为该值不会更改。您最好改用其他属性来控制错误的可见性。