How to bind button to control

Question

I am new to WPF. I have a button on my mainwindow

<Button Grid.Row="1" x:Name="btnSelect" Command="{Binding SaveCommand}"   
      Content="Select" 
     IsEnabled="{Binding CanExec,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 

and in myViewModel

    private bool _canExecute;
    private ICommand saveCommand;
    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
          CreateSaveCommand();

    }
   private void CreateSaveCommand()
    {
        this.saveCommand = new DelegateCommand<object>(this.OnSaveClick,    this.CanSaveExecute);
    }
    public ICommand SaveCommand
    {
        get { return this.saveCommand; }
    }
    private void OnSaveClick(object arg)
    {


    }
    private bool CanSaveExecute(object arg)
    {
        return CanExec;

    }

    public bool CanExec
    {

        get { return _canExecute; }
        set { _canExecute = value; OnPropertyChanged("CanExec"); }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string p)
    {
        if (PropertyChanged == null)
            PropertyChanged(this, new PropertyChangedEventArgs(p));
    }

But the button always remain disabled..What am I missing ??

Answer 1

Your problem is in your implementation of the OnPropertyChanged method... at present, the event will only get called if it is null , which of course, would cause an Exception . Try this instead:

private void OnPropertyChanged(string p)
{
    if (PropertyChanged != null)
        PropertyChanged(this, new PropertyChangedEventArgs(p));
}

---

UPDATE >>>

Your Binding Path is also incorrect, but that would not stop it from working... it should be like this:

<Button Grid.Row="1" x:Name="btnSelect" Command="{Binding SaveCommand}"   
    Content="Select" />

Please note that ICommand.CanExecute does not have to be set to the IsEnabled property manually... the Framework will do that for us.

Answer 2

Bool的默认值为'False'，因此您的CanExec返回'False'并且您的按钮被禁用。