CODEWITHSUNDEEP
c#wpfxamllistviewuser-controls
Jonathan
Jonathan

Reputation: 161

How to disable a button if no items are selected in a ListView

I have a ListView Contained in a UserControl I would like to disabled a button when no items are selected in the UserControl, would it be the right way to do it? So far, it doesn't disable, it just stays enable all the way. I've included the xaml code.

searchAccountUserControl is the UserControl name property in the xaml. And AccountListView is the ListView name property in the userControl xaml.

<Button Content="Debit" IsEnabled="true" HorizontalAlignment="Left" Margin="18,175,0,0" Name="DebitButton" Width="128" Grid.Column="1" Height="32" VerticalAlignment="Top" Click="DebitButton_Click">
        <Button.Style>
            <Style TargetType="Button">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding ElementName=searchAccountUserControl.AccountListView, Path=SelectedValue}" Value="{x:Null}" >
                        <Setter Property="Button.IsEnabled" Value="false"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </Button.Style>
    </Button>

Thanks.

Finally i've used :

in my ViewModel : 

private bool _isSelected;
public bool IsSelected { get { return _isSelected; } 
set { _isSelected = _account.View.CurrentItem != null;       
PropertyChanged.SetPropertyAndRaiseEvent(this, ref _isSelected, value,  
ReflectionUtility.GetPropertyName(() => IsSelected)); } }

And then Use isEnabled = "{Binding Path=IsSelected}" in the xaml.

Upvotes: 2

Views: 12285

Answers (2)

brunnerh
brunnerh

Reputation: 184386

There are a few things wrong here.

  1. Precedence, if you set IsEnabled on the control itself the style will never be able to change it.

  2. ElementName, it's an ElementName, not a path, just one string that gives the name of one element. Everything beyond that goes into the Path.

  3. Style syntax, if you set a Style.TargetType you should not set the Setter.Property with a type prefix (although leaving it does not break the setter).

By the way, this alone is enough:

<Button IsEnabled="{Binding SelectedItems.Count, ElementName=lv}" ...

Upvotes: 25

myermian
myermian

Reputation: 32505

It's obvious that you aren't using Commanding (ICommand Interface). You should either use that (and preferably the Model-View-ViewModel architecture).

But, if you want to stick with code-behind and XAML:

<ListView SelectionChanged="AccountListView_SelectionChanged" ... />

private void AccountListView_SelectionChanged(Object sender, SelectionChangedEventArgs args)
{
    DebitButton.IsEnabled = (sender != null);

    //etc ...
}

More information on MVVM: http://msdn.microsoft.com/en-us/magazine/dd419663.aspx

You need to set the DataContext of the View (UserControl) to the instance of the ViewModel you want to use. Then, from there, you can bind to properties on the ViewModel, including ICommands. You can either use RelayCommand (see link above) or use Commanding provided by a framework (for example, Prism provides a DelegateCommand). These commands take an Action (Execute) and a Func (CanExecute). Simply provide the logic in your CanExecute. Of course, you'd also have to have your ListView SelectedItem (or SelectedValue) be databound to a property on your ViewModel so you can check to see if it's null within your CanExecute function.

Assuming you use RelayCommand you don't have to explicitly call the RaiseCanExecuteChanged of an ICommand.

public class MyViewModel : ViewModelBase //Implements INotifyPropertyChanged
{
    public MyViewModel()
    {
        DoSomethingCommand = new RelayCommand(DoSomething, CanDoSomething);
    }

    public ObservableCollection<Object> MyItems { get; set; }
    public Object SelectedItem { get; set; }

    public RelayCommand DoSomethingCommand { get; set; }


    public void DoSomething() { }

    public Boolean CanDoSomething() { return (SelectedItem != null); }
}
<ListView ItemsSource="{Binding MyItems}" SelectedItem="{Binding SelectedItem}" ... />
<Button Command="{Binding DoSomethingCommand}" ... />

Upvotes: 2

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