如何从WPF中的多分辨率.ico文件中选择正确的大小图标？

Question

如果我有一个多分辨率图标文件(.ico),我怎样才能确保WPF选择合适的图标？设置Image的宽度和高度是否会强制它,或者WPF是否只调整ico文件中的第一个图标？

这就是我目前正在使用的(它有效,但我想避免调整大小,如果这是正在发生的事情).

<MenuItem.Icon>
    <Image Source="MyIcons.ico" Width="16" Height="16"  />
</MenuItem.Icon>

如果可能的话,我想在Xaml中声明这一点,而无需为其编写代码.

Answer 1

我使用简单的标记扩展:

/// <summary>
/// Simple extension for icon, to let you choose icon with specific size.
/// Usage sample:
/// Image Stretch="None" Source="{common:Icon /Controls;component/icons/custom.ico, 16}"
/// Or:
/// Image Source="{common:Icon Source={Binding IconResource}, Size=16}"
/// </summary> 
public class IconExtension : MarkupExtension
{
    private string _source;

    public string Source
    {
        get
        {
            return _source;
        }
        set
        {
            // Have to make full pack URI from short form, so System.Uri recognizes it.
           _source = "pack://application:,,," + value;
        }
    }

    public int Size { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var decoder = BitmapDecoder.Create(new Uri(Source), 
                                           BitmapCreateOptions.DelayCreation,
                                           BitmapCacheOption.OnDemand);

        var result = decoder.Frames.SingleOrDefault(f => f.Width == Size);
        if (result == default(BitmapFrame))
        {
            result = decoder.Frames.OrderBy(f => f.Width).First();
        }

        return result;
    }

    public IconExtension(string source, int size)
    {
        Source = source;
        Size = size;
    }

    public IconExtension() { }
}

Xaml用法:

<Image Stretch="None"
       Source="{common:Icon Source={Binding IconResource},Size=16}"/>

要么

<Image Stretch="None"
       Source="{common:Icon /ControlsTester;component/icons/custom-reports.ico, 16}" />

Answer 2

（基于 @Nikolay 很好的答案和关于绑定的后续评论）

您可能最好创建 aConverter而不是 a MarkupExtension，以便您可以利用Binding. 使用@Nikolay 提供的相同逻辑

    /// <summary>
    /// Forces the selection of a given size from the ICO file/resource. 
    /// If the exact size does not exists, selects the closest smaller if possible otherwise closest higher resolution.
    /// If no parameter is given, the smallest frame available will be selected
    /// </summary>
    public class IcoFileSizeSelectorConverter : IValueConverter
    {
        public virtual object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            var size = string.IsNullOrWhiteSpace(parameter?.ToString()) ? 0 : System.Convert.ToInt32(parameter);

            var uri = value?.ToString()?.Trim();
            if (string.IsNullOrWhiteSpace(uri))
                return null;

            if (!uri.StartsWith("pack:"))
                uri = $"pack://application:,,,{uri}";

            var decoder = BitmapDecoder.Create(new Uri(uri),
                                              BitmapCreateOptions.DelayCreation,
                                              BitmapCacheOption.OnDemand);

            var result = decoder.Frames.Where(f => f.Width <= size).OrderByDescending(f => f.Width).FirstOrDefault()
                ?? decoder.Frames.OrderBy(f => f.Width).FirstOrDefault();

            return result;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }

然后，您必须像平常一样从 ResourceDictionary 中的转换器类创建资源：

<localConverters:IcoFileSizeSelectorConverter x:Key="IcoFileSizeSelector" />

然后你可以使用Binding：

<Image Source="{Binding Path=IconResource, Converter={StaticResource IcoFileSizeSelector}, ConverterParameter=16}" />

PS：在转换器代码中，我们接受所有参数输入，即使是缺失或无效的参数。如果您像我一样喜欢使用实时 XAML 编辑，那么这种行为会更方便。