WPF，命令可以执行了，按钮为什么还是灰色的？

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<Window.DataContext>
    <local:MainWindowViewModel/>
</Window.DataContext>
<Grid HorizontalAlignment="Left" Height="319" VerticalAlignment="Top" Width="527">
    <ListBox ItemsSource="{Binding People}" SelectedItem="{Binding SelectPerson}" DisplayMemberPath="Name" 
            HorizontalAlignment="Left" Height="112" Margin="19,36,0,0" VerticalAlignment="Top" Width="123"/>
    <Button Command="{Binding RemoveCommand}" Content="删除" HorizontalAlignment="Left" Margin="171,129,0,0" 
        VerticalAlignment="Top" Width="75"/>
    <TextBox Text="{Binding SelectPerson.Name}" HorizontalAlignment="Left" Height="23" Margin="197,44,0,0" 
            TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    <TextBox Text="{Binding SelectPerson.Age}" HorizontalAlignment="Left" Height="23" Margin="196,84,0,0" 
            TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    <TextBlock HorizontalAlignment="Left" Margin="161,50,0,0" TextWrapping="Wrap" Text="姓名" VerticalAlignment="Top"/>
    <TextBlock HorizontalAlignment="Left" Margin="161,88,0,0" TextWrapping="Wrap" Text="年龄" VerticalAlignment="Top"/>
</Grid>

class NotificationObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

class Person : NotificationObject 
{
    private string name;
    public string Name      
    {
        get { return name; }
        set {
            name = value;
            OnPropertyChanged("Name");
        }
    }
    private Nullable<int> age;
    public Nullable<int> Age  
    {
        get { return age; }
        set {
                age = value;
                OnPropertyChanged("Age");
            }
    }        
}

class DelegateCommand : ICommand  
{
    public bool CanExecute(object parameter)
    {
        if (CanExecuteFunc == null)
        {
            return true;
        }
        return CanExecuteFunc(parameter);
    }
    public event EventHandler CanExecuteChanged;
    public void Execute(object parameter)
    {
        ExecuteAction(parameter);
    }
    public Action<object> ExecuteAction { get; set; }
    public Func<object, bool> CanExecuteFunc { get; set; }
    public DelegateCommand(Action<object> Execute, Func<object, bool> CanExecute)
    {
        CanExecuteChanged = (x, y) => { }; 
        ExecuteAction = Execute;
        CanExecuteFunc = CanExecute;
    }
} 

class MainWindowViewModel : NotificationObject
{
    private ObservableCollection<Person> people;
    public ObservableCollection<Person> People
    {
        get { return people; }
        set
        {
            people = value;
            this.OnPropertyChanged("People");
        }
    }
    private Person selectPerson;
    public Person SelectPerson
    {
        get { return selectPerson; }
        set
        {
            selectPerson = value;
            this.OnPropertyChanged("SelectPerson");
        }
    }
    public DelegateCommand RemoveCommand { get; set; }
    void RemoveExecute(object param)
    {
        People.Remove(SelectPerson);
    }
    bool RemoveCanExecute(object param)
    {
        if (SelectPerson == null)
            return false;
        return true;
    }
    public MainWindowViewModel()
    {
        People = new ObservableCollection<Person>() 
        {
            new Person(){Name="张三",Age=43},
            new Person(){Name="李四",Age=45},
            new Person(){Name="汤姆",Age=44},
        };
        RemoveCommand = new DelegateCommand(RemoveExecute, RemoveCanExecute);
    }
}

上面的示例，是一个以MVVM模式写的代码。Button的Command绑定RemoveCommand命令上，当在ListBox中选择项的时候，可以执行删除命令了，为什么Button还是灰色的呢？

[q107770540]

上帖你没给出class DelegateCommand : ICommand 的定义

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引用 2 楼 q107770540 的回复:

上帖你没给出class DelegateCommand : ICommand 的定义

嗯,这贴给出了

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有人知道吗？

[Andy__Huang]

.xaml.cs文件有没有这样？

//类名：OrderReportUploadLog

public partial class OrderReportUploadLog : ChildWindow
{
    public OrderReportUploadLog()
    {
        InitializeComponent();
    }

    private void OKButton_Click(object sender, RoutedEventArgs e)
    {
        this.DialogResult = true;
    }


}

还有：

bool RemoveCanExecute(object param)
{
    if (SelectPerson == null)
        return false;
    return true;
}
改为：
private bool RemoveCanExecute(object param)
{
    return true;
}

[Andy__Huang]

private Person selectPerson; public Person SelectPerson 你这样定义可能自己都混淆，建议改为 private Person _SelectPerson; public Person SelectPerson 这样看起来明显一些

[MicrosoftCenterOfHN]

    class DelegateCommand : ICommand
    {
        public bool CanExecute(object parameter)
        {
            if (CanExecuteFunc == null)
            {
                return true;
            }
            return CanExecuteFunc(parameter);
        }
        public void Execute(object parameter)
        {
            ExecuteAction(parameter);
        }
        public Action<object> ExecuteAction { get; set; }
        public Func<object, bool> CanExecuteFunc { get; set; }
        public DelegateCommand(Action<object> Execute, Func<object, bool> CanExecute)
        {
            ExecuteAction = Execute;
            CanExecuteFunc = CanExecute;
        }

        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }
    }

你的DelegateCommand的问题，试试上面的代码。 主要是CanExecuteChanged的定义。

[小猪八Q]

DelegateCommand的第二个参数不是你想的那样，CanExecute是在window的InitializeComponent();的时候触发的，来判断是否可点击和执行，这个适合权限管理的那种，在CanExecute中加入权限判断的code，这是很方便的。 至于DelegateCommand以及内部更深层次的东西我不了解，而且在现有代码的基础上修改也无法完成，你可以使用另外一种方法，就是Converter

IsEnabled="{Binding Path=SelectedItem,ElementName=listbox,Converter={StaticResource xxx}}"

在Converter中判断，如果为null，则返回false，否则返回true 参考下吧，希望能帮到你

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引用 7 楼 MicrosoftCenterOfHN 的回复:

你的DelegateCommand的问题，试试上面的代码。 主要是CanExecuteChanged的定义。

果然是这个问题诶，我想请问下， public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } 这个是什么语法哦，匿名方法吗？value是什么意思？

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引用 7 楼 MicrosoftCenterOfHN 的回复:

主要是CanExecuteChanged的定义。

果然是这个问题诶，我想请问下， public event EventHandler CanExecuteChanged { add { CommandManager.RequerySuggested += value; } remove { CommandManager.RequerySuggested -= value; } } 这个是什么语法哦，匿名方法吗？value是什么意思？