XAML 为什么在使用IMultiValueConverter时，我的值在object[]值中为空，但在视图中不使用它时似乎有值？

3hvapo4f 于 2023-09-28 发布在其他

关注(0)|答案(1)|浏览(95)

请帮助我理解这一点。我的视图中有以下内容：

<Label 
    x:Name="communityAndUserLabel"
    Grid.Row="2"
    Grid.Column="1"
    FontAttributes="None"
    VerticalOptions="End">
    <Label.Text>
        <MultiBinding StringFormat="{}{0} • {1}">
            <Binding Path="CommunityName" />
            <Binding Path="Username" />
        </MultiBinding>
    </Label.Text>
    <Label.TextColor>
        <MultiBinding Converter="{StaticResource CommunityTextColorConverter}">
            <Binding Path="CommunityName" 
                Source="x:Reference communityAndUserLabel" />
            <Binding Path="Username" 
                Source="x:Reference communityAndUserLabel" />
        </MultiBinding>
    </Label.TextColor>
</Label>

当应用程序运行时，CommunityName和Username显示为按照Label. TextStringFormat指定的格式然而，当满足标准时，不发生颜色变化。我发现这是因为object[] values在开始时似乎没有将任何数据放入CommunityTextColorConvertor.cs文件中，因此所有内容都计算为null/empty。
CommunityTextColorConverter.cs：

using System.Globalization;

namespace Disc.Converters
{
    public class CommunityTextColorConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        { // Check if the values are valid if (values == null || values.Length != 2) return Colors.Black;

            // Get the community name and username from the values array
            string CommunityName = values[0] as string;

            // Check if the community name and username are not null or empty
            if (string.IsNullOrEmpty(CommunityName))
            {
                return Colors.PowderBlue; //default color when unset
            }

            // Define some colors for different communities
            Color red = Color.FromRgb(255, 0, 0);
            Color green = Color.FromRgb(0, 255, 0);
            Color blue = Color.FromRgb(0, 0, 255);

            // Return a different color based on the community name
            switch (CommunityName.ToLower())
            {
                case "nintendo":
                    return red;
                case "xbox":
                    return green;
                case "playstation":
                    return blue;
                case "pcgaming":
                    return Colors.Purple;
                case "news":
                    return Colors.Pink;
                default:
                    return Colors.PowderBlue;
            }
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            // Not implemented
            throw new NotImplementedException();
        }
    }
}

我试过的东西：

在Label.TextColor元素中设置BindingPath =“Text”
在Label.TextColor元素中设置BindingPath =“CommunityName”（另一个设置Username）
再次运行它而不改变任何东西，希望它会神奇地工作，这一次

xaml

来源：https://stackoverflow.com/questions/76860258/why-are-my-values-empty-in-object-values-when-using-imultivalueconverter-but

1条答案

按热度按时间

nwlqm0z11#

我能够得到拉入的值，这在技术上是我的问题-所以我想我应该张贴‘解决方案‘作为答案？Julian提到绑定源代码是错误的，这让我走上了正确的道路。它仍然不像我试图做的那样工作（只能让整个字符串显示为一种颜色），但更新的（半）工作代码如下：

NameColorMultiConverter.cs

using System.Globalization;

namespace Disc.Converters
{
    public class NameColorMultiConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            Console.WriteLine("CommunityName: " + values[0]);
            Console.WriteLine("Username: " + values[1]);
            // Check if the input values are strings
            if (values[0] is not string community || values[1] is not string username)
                return Colors.Black;

            // Define an array of known community names
            string[] communities = new[] 
            { 
                "PlayStation", 
                "Xbox", 
                "PCGaming", 
                "Nintendo",
                "Discuit"
            };

            // Define a switch expression to map community names to colors
            Color communityColor = community switch
            {
                "PlayStation" => Colors.Blue,
                "Xbox" => Colors.Green,
                "PCGaming" => Colors.Purple,
                "Nintendo" => Colors.Red,
                "Discuit" => Colors.Purple,
                // Add more cases as needed
                _ => Colors.Aqua // Default case
            };

            // Define an array of known usernames
            string[] usernames = new[]
            {
                "Previnder",
                "ReticentRobot",
                "TestAccountPlsIgnore",
                "RenegadeBAM",
                "gsurfer04"
            };

            // Define a switch expression to map usernames to colors
            Color usernameColor = username switch
            {
                "Previnder" => Colors.Red,
                "ReticentRobot" => Colors.Orange,
                "TestAccountPlsIgnore" => Colors.Yellow,
                "RenegadeBAM" => Colors.Green,
                "gsurfer04" => Colors.Blue,
                // Add more cases as needed
                _ => Colors.Pink // Default case
            };

            // Return the color for the community name or the username based on the parameter value
            return parameter switch
            {
                "community" => communityColor,
                "username" => usernameColor,
                _ => Colors.AntiqueWhite // Default case
            };
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            // This converter does not support converting back
            throw new NotImplementedException();
        }
    }
}

附带XAML

<Label 
    x:Name="communityAndUserLabel"
    Grid.Row="2"
    Grid.Column="1"
    FontAttributes="None"
    VerticalOptions="End">
    <Label.Text>
        <MultiBinding StringFormat="{}{0} • {1}" Mode="TwoWay">
            <Binding Path="CommunityName" />
            <Binding Path="Username" />
        </MultiBinding>
    </Label.Text>
    <Label.TextColor>
        <MultiBinding Converter="{StaticResource nameColorMulti}" ConverterParameter="community">
            <Binding Path="CommunityName" />
            <Binding Path="Username" />
        </MultiBinding>
    </Label.TextColor>
</Label>

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我来回答

XAML 为什么在使用IMultiValueConverter时，我的值在object[]值中为空，但在视图中不使用它时似乎有值？

1条答案

NameColorMultiConverter.cs

附带XAML

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