.NET MAUI自定义Handler报CS0131：赋值左侧需为变量、属性或索引器

错误根源 #

1. MapText方法的第一个参数类型错误：传入了EntryHandler，但实际应该是自定义的CustomEntryHandler，类型不匹配导致编译器无法正确识别handler.PlatformView的赋值操作。
2. 自定义控件接口ICustomEntry的属性仅定义了get访问器，不符合MAUI属性映射的双向赋值要求。

修复方案 #

1. 修正MapText方法的参数类型 #

将MapText的第一个参数改为CustomEntryHandler，确保类型匹配：

private static void MapText(CustomEntryHandler handler, ICustomEntry entry)
{
    handler.PlatformView?.Text = entry.Text;
}

2. 更新接口的属性访问器 #

给ICustomEntry的属性添加set访问器，支持双向赋值：

public interface ICustomEntry : IView
{
    public string Text { get; set; }
    public Color TextColor { get; set; }
}

3. 完整的修正后代码 #

CustomEntryHandler

public partial class CustomEntryHandler : ViewHandler<ICustomEntry, EditText>
{
    private static PropertyMapper<ICustomEntry, CustomEntryHandler> CustomEntryMapper = new(ViewMapper)
    {
        [nameof(ICustomEntry.Text)] = MapText,
    };

    public CustomEntryHandler(CommandMapper commandMapper = null) : base(CustomEntryMapper, commandMapper)
    {
    }

    protected override EditText CreatePlatformView()
    {
        return new EditText(Context);
    }

    private static void MapText(CustomEntryHandler handler, ICustomEntry entry)
    {
        handler.PlatformView?.Text = entry.Text;
    }
}

接口与自定义控件类

public interface ICustomEntry : IView
{
    public string Text { get; set; }
    public Color TextColor { get; set; }
}

public class CustomEntry : View, ICustomEntry
{
    public string Text { get; set; }
    public Color TextColor { get; set; }
}

内容的提问来源于stack exchange，提问作者Marco Antonio Luna Serrano