c# - IValueConverter 和可见性

Question

我有一个具有 3 种通信状态的应用程序:已连接、已断开连接和待处理。通信状态由一些其他参数控制。我想在 IValueConverter 控制的屏幕上显示相应的图像。但我无法让它工作。

这是我包含 3 张图片的 Xaml 代码:

<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" />

这里是控制CommunitationState的方法

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;
    }
}

最后但同样重要的是转换器:

  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();
        }
    }

数据绑定(bind)工作正常。我知道肯定是因为我有一个文本框绑定(bind)了另一种将状态显示为文本的方法。我的转换器被调用，我肯定知道这一点，因为我可以在其中放置一个断点。

所以我的转换器出了点问题，因为我总是以折叠的图像结束。

**** 编辑 ****

这是我的 debug.Writeline 的一些输出

我启动连接:

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

我改为pending:

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

我启动挂起:

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

这是正确的，因为我的程序默认连接，一秒钟后它意识到它无法看到 TCP 服务器但仍然可以访问 Wifi，所以我将状态更改为挂起。

Answer 1

根据您的评论，很可能是您的 ConnectionWithServerEstablished 属性没有更改以使图像可见和/或您没有触发 PropertyChanged 事件值(value)改变了。

例如，您可以通过在依赖属性的 setter 中触发事件来执行此操作:

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

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

您用作 DataContext(您的 ViewModel)的类当然必须为此实现 INotifyPropertyChanged。