Xamarin Forms：可绑定属性的 IMarkupExtension 不起作用

Question

绑定不适用于图像标记。当我调试时，我看到Extension class 中的Source 的值总是为null？但是标签内容不为空

Xaml

<Label Text="{Binding Image}" />
<Image Source="{classes:ImageResource Source={Binding Image}}" />

ImageResourceExtension

// You exclude the 'Extension' suffix when using in Xaml markup
[Preserve(AllMembers = true)]
[ContentProperty("Source")]
public class ImageResourceExtension : BindableObject, IMarkupExtension
{
    public static readonly BindableProperty SourceProperty = BindableProperty.Create(nameof(Source), typeof(string), typeof(string), null);
    public string Source
    {
        get { return (string)GetValue(SourceProperty); }
        set { SetValue(SourceProperty, value); }
    }

    public object ProvideValue(IServiceProvider serviceProvider)
    {
        if (Source == null)
            return null;

        // Do your translation lookup here, using whatever method you require
        var imageSource = ImageSource.FromResource(Source);

        return imageSource;
    }
}

Answer 1

当然不是！

并不是因为您从 BindableObject 继承，所以您的对象神奇地具有 BindingContext 集。如果没有 BindingContext，就无法解析 {Binding Image}.

您要找的是转换器

class ImageSourceConverter : IValueConverter
{
    public object ConvertTo (object value, ...)
    {
        return ImageSource.FromResource(Source);
    }

    public object ConvertFrom (object value, ...)
    {
        throw new NotImplementedException ();
    }
}

然后将此转换器添加到您的 Xaml 根元素资源（或 Application.Resources 并在您的绑定中使用它

<Label Text="{Binding Image}" />
<Image Source="{Binding Image, Converter={StaticResource myConverter}}" />

Xamarin Forms：可绑定属性的 IMarkupExtension 不起作用

Xamarin Forms: IMarkupExtension with bindable property does not work

image

xamarin

xamarin.forms

data-binding

bindable

Xaml

ImageResourceExtension

Xamarin Forms：可绑定 属性 的 IMarkupExtension 不起作用

Xamarin Forms: IMarkupExtension with bindable property does not work

image

xamarin

xamarin.forms

data-binding

bindable

Xaml

ImageResourceExtension

Xamarin Forms：可绑定属性的 IMarkupExtension 不起作用