Xamarin.Forms列表视图

我正在制作词汇应用程序，并尝试在Xamarin.Forms列表视图中实现最喜欢的单词

请看下面的截图

现在我使用硬代码而不是MVVM 这是我的模型

namespace Mamtil.Models
{
    public class Word
    {
        public int Id { get; set; }
        public string word { get; set; }
        public string translation { get; set; }
        public string audio { get; set; }
        public bool favorite { get; set; }
        public string groupBy => translation[0].ToString().ToUpper();
    }
}

XAML

举例来说：

...
// Some thing like
if(Word.favorite)
    Image = yellow_star.png;
else
    Image = gray_star.png;

我应该在代码中还是在XAML中执行它

---

我希望你能清楚地描述我的问题。提前感谢

您可以将图像的

源

绑定到文件、Uri或资源，从而设置要显示的图像

• FromFile-需要可在每个平台上解析的文件名或文件路径
• FromUri-需要一个Uri对象，例如新Uri（“”）
• FromResource-需要嵌入到应用程序或PCL中的映像文件的资源标识符，并具有生成操作：EmbeddedResource

XAML：

 <Image Source="{Binding MyImage}" />

---

您可以阅读有关使用图像的更多信息

您必须使用

OnPropertyChanged（）

方法，以便它拾取图像Url的新值，并且您还应该设置绑定上下文

private bool _imageUrl;
public bool ImageUrl
{
    get { return _imageUrl; }
    set { _imageUrl = value; OnPropertyChanged(); }
}

---

并使用

BindingContext=this在构造函数中。
一篇旧文章，但这里有另一种方法。
经典的做法是使用转换器。
您的按钮XAML现在看起来像这样：

<Button x:Name="FavoriteButton" Image="{Binding favorite, Converter={x:Static converter:FavoriteButton.Instance}}" BackgroundColor="#F5F5F5" Clicked="Favorite" BorderRadius="0" WidthRequest="45" CommandParameter="{Binding .}" />

namespace Mamtil.Converter {
public class FavoriteButton : IValueConverter {
// this Instance property just means your converter only needs to get created once, I saw it in a Xamarin sample.
    public static FavoriteButton Instance = new FavoriteButton(); 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        if (value == null) {
            // only doing this because I've had encounters where an ImageSource has taken Exception at having null returned.
            return ImageSource.FromFile("gray_star.png");
        }
        var fav = (bool)value;
        if (fav == true) { // redundant ==, but it makes it quite explicit for any future reader glancing over your code what you intend here.
            return ImageSource.FromFile("yellow_star.png");
        }
        return ImageSource.FromFile("gray_star.png");
    }

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

转换器的外观如下所示：

<Button x:Name="FavoriteButton" Image="{Binding favorite, Converter={x:Static converter:FavoriteButton.Instance}}" BackgroundColor="#F5F5F5" Clicked="Favorite" BorderRadius="0" WidthRequest="45" CommandParameter="{Binding .}" />

namespace Mamtil.Converter {
public class FavoriteButton : IValueConverter {
// this Instance property just means your converter only needs to get created once, I saw it in a Xamarin sample.
    public static FavoriteButton Instance = new FavoriteButton(); 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        if (value == null) {
            // only doing this because I've had encounters where an ImageSource has taken Exception at having null returned.
            return ImageSource.FromFile("gray_star.png");
        }
        var fav = (bool)value;
        if (fav == true) { // redundant ==, but it makes it quite explicit for any future reader glancing over your code what you intend here.
            return ImageSource.FromFile("yellow_star.png");
        }
        return ImageSource.FromFile("gray_star.png");
    }

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

如果您使用的是嵌入式资源而不是本地文件，请参考Rohit于2016年8月24日在其答案中发布的链接，了解如何在转换器中使用这些资源的指导。
或转换器是解决您问题的最佳方案

<Button Image="gray_star.png">
    <Button.Triggers>
        <DataTrigger TargetType="Button" Binding="{Binding favorite}" Value="True">
            <Setter Property="Image" Value="yellow_star.png" />
        </DataTrigger>
    </Button.Triggers>
</Button>



xmlns:converter="clr-namespace:Mamtil.Converter;assembly=Interact.Client"

namespace Mamtil.Converter {
public class FavoriteButton : IValueConverter {
// this Instance property just means your converter only needs to get created once, I saw it in a Xamarin sample.
    public static FavoriteButton Instance = new FavoriteButton(); 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        if (value == null) {
            // only doing this because I've had encounters where an ImageSource has taken Exception at having null returned.
            return ImageSource.FromFile("gray_star.png");
        }
        var fav = (bool)value;
        if (fav == true) { // redundant ==, but it makes it quite explicit for any future reader glancing over your code what you intend here.
            return ImageSource.FromFile("yellow_star.png");
        }
        return ImageSource.FromFile("gray_star.png");
    }

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

<Button Image="gray_star.png">
    <Button.Triggers>
        <DataTrigger TargetType="Button" Binding="{Binding favorite}" Value="True">
            <Setter Property="Image" Value="yellow_star.png" />
        </DataTrigger>
    </Button.Triggers>
</Button>