无法识别c# WPF MVVM Light CanExecute

本文关键字：MVVM Light CanExecute WPF 识别 | 更新日期: 2023-09-27 18:11:46

我现在正在学习WPF和MVVM，遇到了一点问题。

我使用MVVM灯，我希望一些按钮在验证后被禁用/启用，但它不使用功能。

ViewModelMain: 

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Entity;
namespace EF_MVVM_Test
{
    public class ViewModelMain : ViewModelBase
    {
        public RelayCommand AddAuthorCommand { get; private set; }
        public RelayCommand DeleteAuthorCommand { get; private set; }
        public RelayCommand RefreshCommand { get; private set; }
        public RelayCommand SaveCommand { get; private set; }
        public ObservableCollection<Author> Authors { get; set; }
        private LibraryContext db;
        private Author _SelectedAuthor;
        public Author SelectedAuthor
        {
            get { return _SelectedAuthor; }
            set { Set("SelectedAuthor", ref _SelectedAuthor, value); }
        }
        private Author _NewAuthor;
        public Author NewAuthor
        {
            get { return _NewAuthor; }
            set { Set("NewAuthor", ref _NewAuthor, value); }
        }
        public ViewModelMain()
        {
            db = new LibraryContext();
            db.Author.Load();
            Authors = db.Author.Local;
            AddAuthorCommand = new RelayCommand(ExecuteAddAuthorCommand, CanExecuteAddAuthorCommand);
            DeleteAuthorCommand = new RelayCommand(ExecuteDeleteAuthorCommand, CanExecuteDeleteAuthorCommand);
            RefreshCommand = new RelayCommand(ExecuteRefreshListCommand);
            SaveCommand = new RelayCommand(ExecuteSaveCommand);
            NewAuthor = new Author();
        }
        private void ExecuteAddAuthorCommand()
        {
            db.Author.Add(_NewAuthor);
            NewAuthor = new Author();
        }
        private void ExecuteDeleteAuthorCommand()
        {
            db.Author.Remove(SelectedAuthor);
        }
        private void ExecuteRefreshListCommand()
        {
            db.Author.Load();
            Authors = db.Author.Local;
        }
        private void ExecuteSaveCommand()
        {
            db.SaveChanges();
        }
        private bool CanExecuteAddAuthorCommand()
        {
            return (!string.IsNullOrEmpty(NewAuthor.Name) && NewAuthor.Birthday != null);
        }
        private bool CanExecuteDeleteAuthorCommand()
        {
            return SelectedAuthor != null;
        }
    }
}
XAML: 

<StackPanel>
        <DataGrid ItemsSource="{Binding Authors}" SelectedItem="{Binding SelectedAuthor}" AutoGenerateColumns="False" Height="200" Margin="5" CanUserAddRows="False" CanUserDeleteRows="False">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Name" Binding="{Binding Name}"/>
                <DataGridTextColumn Header="Birthday" Binding="{Binding Birthday}"/>
            </DataGrid.Columns>
        </DataGrid>
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Name" Margin="5" VerticalAlignment="Center"/>
            <TextBox Height="25" Width="70" Margin="5" Text="{Binding NewAuthor.Name}"/>
            <TextBlock Text="Geburtstag" Margin="5" VerticalAlignment="Center"/>
            <DatePicker Height="25" Width="130" Margin="5" SelectedDate="{Binding NewAuthor.Birthday}"/>
            <Button Margin="5" Height="25" Width="80" Content="Hinzufügen" HorizontalAlignment="Left" Command="{Binding AddAuthorCommand}"/>
            <Button Margin="5" Height="25" Width="80" Content="Löschen" HorizontalAlignment="Left" Command="{Binding DeleteAuthorCommand}"/>
        </StackPanel>
        <StackPanel Orientation="Horizontal">
            <Button Width="120" Height="25" Content="Speichern" HorizontalAlignment="Left" Margin="5" Command="{Binding SaveCommand}"/>
            <!--Button Width="120" Height="25" Content="Aktualisieren" HorizontalAlignment="Left" Margin="5" Command="{Binding RefreshCommand}"/-->
        </StackPanel>
</StackPanel>

知道为什么按钮不使用canexecute函数吗?

无法识别c# WPF MVVM Light CanExecute

您的问题是您使用的名称空间:

using GalaSoft.MvvmLight.Command;

替换为:

using GalaSoft.MvvmLight.CommandWpf;

WPF的CommandManager在检测到UI更改时调用CanExecute ?什么构成了UI更改?添加和删除元素，一些绑定更新，视觉状态更改。基本上，只要WPF想这样做。这是不可靠的。

你怎么能避开这个?当需要刷新RelayCommand时，呼叫RelayCommand.RaiseCanExecuteChanged()。此方法引发一个事件，通知WPF它应该重新评估命令的状态。

看来你几天前和我有同样的问题。

ICommand doesn't work

ICommand.CanExecute不调用，因为你当然不会说按钮:"当我在TextBox中插入一些东西时，按钮单击的能力可能会改变"。所以你的按钮没有意识到，如果文本框的文本发生变化，他可以被启用。您必须显式地告诉按钮，当文本发生变化时，它应该检查ICommand.CanExecute，方法是在文本框tex发生变化时引发ICommand.CanExecuteChanged事件。

我认为，不幸的是，你必须调用RelayCommand对象的RaiseCanExecuteChanged方法后分配SelectedAuthor和拦截NewAuthor对象的属性更改

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