IValueConverter and Visibility

问题

I have an application with 3 comunicationstates: Connected, Disconnected and Pending. The communication state are controled by some other paramers. I want to display the corresponding image on the screen controlled by an IValueConverter. But I cant get it to work.

Heres is my Xaml code for includeing the 3 images :

<Image x:Name="connectedImage"  
    Visibility="{Binding ConnectionWithServerEstablished, Converter={StaticResource communitationStateToVisibilityConverter}, ConverterParameter=ConverterParameterConnected}"
    Source="Assets/connected.png"
    Stretch="None"
    HorizontalAlignment="Center" />



<Image x:Name="disconnectedImage"
    Visibility="{Binding ConnectionWithServerEstablished, Converter={StaticResource communitationStateToVisibilityConverter}, ConverterParameter=ConverterParameterDisconnected}"
    Source="Assets/disconnect.png"
    Stretch="None"
    HorizontalAlignment="Center" />


<Image x:Name="pendingImage"
    Visibility="{Binding ConnectionWithServerEstablished, Converter={StaticResource communitationStateToVisibilityConverter}, ConverterParameter=ConverterParameterPending}"
    Source="Assets/pending.png"
    Stretch="None"
    HorizontalAlignment="Center" />

Here is the methos controlling CommunitationState

public enum CommunitationState { Connected, Disconnected, Pending }

public CommunitationState ConnectionWithServerEstablished
{
    get
    {
        if (IRCommandSent)
            return CommunitationState.Disconnected;

        if (wifiConnected && !fcConnected)
            return CommunitationState.Pending;

        return wifiConnected ? CommunitationState.Connected : CommunitationState.Disconnected;
    }
}

And last but not least the converter:

  public class CommunitationStateToVisibilityConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, string language)
        {
            var result = Visibility.Collapsed;

            if ((string)parameter == "ConverterParameterConnected")
                result = (CommunitationState)value == CommunitationState.Connected ? Visibility.Visible : Visibility.Collapsed;

            if ((string)parameter == "ConverterParameterDisconnected")
                result = (CommunitationState)value == CommunitationState.Disconnected ? Visibility.Visible : Visibility.Collapsed;

            if ((string)parameter == "ConverterParameterPending")
                result = (CommunitationState)value == CommunitationState.Pending ? Visibility.Visible : Visibility.Collapsed;
            Debug.WriteLine("value={0}, parameter={1}, result={2}", value,   (string)parameter, result);
            return result;
        }

        public object ConvertBack(object value, Type targetType, object parameter, string language)
        {
            throw new NotImplementedException();
        }
    }

The Databinding works like its supposed to do. I know that for sure bacause I have a textbox bound an other method displaying the state as text. My converter gets called, I know that for sure because I can place a break point in it.

So there is something wrong with my converter, because I allways ends up with a collapsed image.

**** EDIT ****

Here are some output from my debug.Writeline

I startup Connected:

value=Connected, parameter=ConverterParameterConnected, result=Visible
value=Connected, parameter=ConverterParameterDisconnected, result=Collapsed
value=Connected, parameter=ConverterParameterPending, result=Collapsed

I change to pending:

value=Pending, parameter=ConverterParameterConnected, result=Collapsed
value=Pending, parameter=ConverterParameterDisconnected, result=Collapsed
value=Pending, parameter=ConverterParameterPending, result=Visible

I startup pending:

value=Connected, parameter=ConverterParameterConnected, result=Visible
value=Connected, parameter=ConverterParameterDisconnected, result=Collapsed
value=Connected, parameter=ConverterParameterPending, result=Collapsed
value=Pending, parameter=ConverterParameterConnected, result=Collapsed
value=Pending, parameter=ConverterParameterDisconnected, result=Collapsed
value=Pending, parameter=ConverterParameterPending, result=Visible

This is correct because my program defaults to connected, and after a second it realizes that it can not see the TCP server but still have acces to Wifi so i changes state to pending.

回答1:

From your comments, it is most likely that your ConnectionWithServerEstablished property does not change to make the images visible and/or you do not fire a PropertyChanged event when the property value changed.

You can do this for example by firing the event in the setter of your dependent properties:

public bool IRCommandSent
{
    set
    {
        // set the value
        // ...

        // notify event listeneers that the ConnectionWithServerEstablished may have changed
        if (PropertyChanged != null)
        {
             PropertyChanged(this, new PropertyChangedEventArgs("ConnectionWithServerEstablished"));
        }
    }
}

The class you use as DataContext (your ViewModel) must of course implement INotifyPropertyChanged for that.

来源：https://stackoverflow.com/questions/26924718/ivalueconverter-and-visibility