c# - WPF XAML : The specified conversion is not valid中的不受控制的异常

我有一个MVVM WPF应用程序。我有下面的转换器:

public class PrintIconVisibilityValueConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        if (values[0] == null || values[1] == null) return Visibility.Collapsed;

        int item1 = (int)values[0];
        string item2 = (string)values[1];

        if (item1 > 0 || !string.IsNullOrEmpty(item2))
        {
            return Visibility.Visible;
        }
        else
        {
            return Visibility.Collapsed;
        }
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

我认为:

<Window.Resources>
   <classes:PrintIconVisibilityValueConverter x:Key="PrintIconVisibilityValueConverter"/>
</Window.Resources>

然后我在此 View 中有一个图像:

<Image Source="/MyImages;component/Images/PrintIco.png"
       Height="15" Margin="20 0 5 0">
    <Image.Visibility>
            <MultiBinding Converter="{StaticResource PrintIconVisibilityValueConverter}">
                <Binding Path="Item1" />
                <Binding Path="Item2" />
            </MultiBinding>
    </Image.Visibility>
</Image>

Item1和Item2是 View 模型中的公共(public)属性:

private string _item2 = string.Empty;
public string Item2
{
    get
    {
        return _item2;
    }

    set
    {
        if (_item2 == value) return;

        _item2 = value;
        OnPropertyChanged("Item2");
    }
}

private int _item1;
public int Item1
{
    get
    {
        return _item1;
    }

    set
    {
        if (_item1 == value) return;

        _item1 = value;
        OnPropertyChanged("Item1");
    }
}

它可以正确编译，并且我可以毫无问题地执行该应用程序，但是在设计时，该 View 没有显示，错误提示“不受控制的异常”并指向该行:

int item1 = (int)values[0];

在PrintIconVisibilityValueConverter类中。

在 View 中显示的异常的屏幕截图下方:

最佳答案

一些建议；

在转换器中调用GetIsInDesignMode方法，如果返回true，则立即返回:

public class PrintIconVisibilityValueConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        if (DesignerProperties.GetIsInDesignMode(new DependencyObject()))
            return Visibility.Visible;
        ...
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

在XAML中设置DataContext:

<Window.DataContext>
    <local:ViewModel />
</Window.DataContext>

设置设计时间数据上下文:

<Window ... d:DataContext ="{d:DesignInstance {x:Type local:ViewModel}, IsDesignTimeCreatable=True}">

或Disable XAML UI designer

关于c# - WPF XAML : The specified conversion is not valid中的不受控制的异常，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/51308281/