WPF，命令可以执行了，按钮为什么还是灰色的？
<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 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 NotificationObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}
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);
}
}
