Question

I am new to wpf and xaml (Windows development in general) and my background is asp.net and prior to that classic ASP.

I’m working on an application that needs to have the button disabled/grayed out while the processing occurs and read a post on here to do the following but it doesn’t appear to be working. What am I missing?

<Window x:Class="SCGen.Application.LoadForecast.EngineExecution"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:igEditors="http://infragistics.com/Editors"        
    SizeToContent="WidthAndHeight"
    Title="Engine Execution"
    ResizeMode="NoResize"
    WindowStartupLocation="CenterOwner"
    Background="{StaticResource {x:Static SystemColors.ControlBrushKey}}">
<Window.Resources>
    <Style TargetType="{x:Type Button}" x:Key="myStyle" BasedOn="{StaticResource ButtonStyle}">
        <Setter Property="Command" Value="{Binding ExecuteEngine}" />
        <Setter Property="Content" Value="Execute Engine" />
        <Style.Triggers>
            <Trigger Property="Command" Value="{x:Null}">
                <Setter Property="IsEnabled" Value="False"/>
            </Trigger>
        </Style.Triggers>
    </Style>
</Window.Resources>    
<Border Padding="8">
    <StackPanel>
        <StackPanel MaxWidth="200" HorizontalAlignment="Left">
            <TextBlock Text="Select Forecast Engine" TextAlignment="Center" FontSize="13" />

            <igEditors:XamComboEditor ItemsSource="{Binding ForecastEngines}" SelectedItem="{Binding SelectedEngine}" Margin="0,5" />

            <Button Style="{StaticResource ResourceKey=myStyle}" />
        </StackPanel>

        <TextBlock Text="{Binding EngineStatus}" FontSize="15" FontStyle="Italic" Margin="0,14" Width="400" TextWrapping="Wrap" />
    </StackPanel>
</Border>

</Window>

I’ve changed the xaml to the following:

<Button Content="Execute Weather Import" Command="{Binding ExecuteWeather}" Style="{StaticResource ButtonStyle}" IsEnabled="{Binding IsEnabled}"/>

In the ViewModel I have the following:

private bool _isEnabled = true;
    public bool IsEnabled
    { 
        get { return _isEnabled; }
        set { _isEnabled = value; }
    }

and I set the _isEnabled here:

private string LaunchWeatherImport(string strVendor)
    {
        _isEnabled = false;

        string uri = ConfigurationManager.AppSettings["ManualExecutionFacilitatorService"];
        ClientConnectionInfo connection = new ClientConnectionInfo(uri) { UseSecurity = true };
        connection.SetTimeouts();

        Logger.LogInfo("Calling Facilitator service to manually import " + strVendor + " weather data.");

        ((NetTcpBinding)connection.Binding).Security.Mode = System.ServiceModel.SecurityMode.None;

        using (var client = new FacilitatorManualExecutionClient(connection))
        {
            client.InnerChannel.OperationTimeout = TimeSpan.FromMinutes(int.Parse(ConfigurationManager.AppSettings["OperationTimeOutMinutes"]));

            try
            {
                _isEnabled = true;
                return "success";
                // uncomment this line before commit
                //return client.ExecuteWeather(strVendor);
            }
            #region catch
            catch (Exception ex)
            {
                Logger.LogError(ex.Message, ex);
                return ex.Message;
            }
            #endregion
        }
    }

I still can’t get it to work properly.

Answer 1

For starters, you’re setting the trigger on the Command property but you don’t have a binding set on that property for your button:

<Button Style="{StaticResource ResourceKey=myStyle}" />

Should be:

<Button Style="{StaticResource ResourceKey=myStyle}" Command="{Binding MyCommand}" />

[Where MyCommand is the name of your actual command that you’re binding to]

I am not so sure that it will work anyway though because your trigger is set to fire when the Command property is null, but if you bind to the command property, following the MVVM pattern then your command property shouldn’t be null so the trigger won’t fire then either.

UPDATE:

You need to implemented the INotifyPropertyChanged interface on your class that has the property.

public class MyClass : System.ComponentModel.INotifyPropertyChanged

Then add the implementation:

public event PropertyChangedEventHandler PropertyChanged;

private void NotifyPropertyChanged(String info)
{
    if (PropertyChanged != null)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(info));
    }
}

Then change your property to be:

private bool _isEnabled = true;
public bool IsEnabled
{ 
    get { return _isEnabled; }
    set 
    { 
       _isEnabled = value;
       NotifyPropertyChanged("IsEnabled");
    }
}