c# - PropertyGrid - 动态加载下拉值

Question

我已经尝试了各种方法——很多都在使用 TypeConverters 等。所以我不会在这里介绍所有这些。

因此，将问题简化为基础。考虑到以下情况：

Imports LiteDB
Imports System.ComponentModel

Public Class mSystem

    <CategoryAttribute("General"), ReadOnlyAttribute(True)>
    Public Property ID As Integer

    Public Property ShortName As String = ""

    <BsonRef("mSystemTypes")>
    Public Property SystemType As mSystemType

End Class

Public Class mSystemType

    <CategoryAttribute("General"), ReadOnlyAttribute(True)>
    Public Property ID As Integer

    Public Property Name As String = "Default"
    Public Property Details As String = ""

End Class

如何将“SystemTypes”作为从 mSystemTypes 集合动态填充的下拉选择器？例如，您选择“控制台”，它会使用匹配的 mSystemType 更新 mSystem。

我正在使用 LiteDb，这可能会使事情变得更加困难，因为它不是像其他场景可能存在的“外键”纯粹的整数，而是一个完整的对象。

我需要维护“dbRef”方法以确保数据关系的完整性。以防万一 DBLite 东西抛出一个曲线球，下面的一些代码演示了它的使用：

Public Class dbCollecitons

    Public mSystems As LiteCollection(Of mSystem)
    Public mSystemTypes As LiteCollection(Of mSystemType)

    Private Sub Examples()

        Dim col As LiteCollection(Of mSystemType) = dbCollections.mSystemTypes
        Dim value as String = "Console"
        Dim q = col.FindAll.Where(Function(x) x.Name = value).First
        Console.Writeline(q.ID)

    End Sub

End Class

LiteDb.LiteCollection 不直接映射到 ICollection（你在 TypeConverter 中使用它？），但我确信有一些解决方法。

标签： c#.netvb.netwinformspropertygrid

Answer 1

简而言之，您需要创建一个新的TypeConverter支持标准值。

示例 - VB.NET

我想你有一个Product类，有一个类型的属性Category，你希望能够从List<Category>运行时来自数据库之类的某个地方进行选择：

Public Class Product
    Public Property Id As Integer
    Public Property Name As String
    <TypeConverter(GetType(CategoryConverter))>
    Public Property Category As Category
End Class

Public Class Category
    Public Property Id As Integer
    Public Property Name As String
    Public Overrides Function ToString() As String
        Return $"{Id} - {Name}"
    End Function
End Class

这是CategoryService可以从您喜欢的任何地方加载类别的类：

Public Class CategoryService
    Private list As List(Of Category) = New List(Of Category) From {
        New Category() With {.Id = 1, .Name = "Category 1"},
        New Category() With {.Id = 2, .Name = "Category 2"},
        New Category() With {.Id = 3, .Name = "Category 3"}
    }
    Public Function GetAll() As IEnumerable(Of Category)
        Return list
    End Function
End Class

下一步是创建CategoryConverter负责为下拉列表提供值的对象：

Imports System.ComponentModel
Public Class CategoryConverter
    Inherits TypeConverter
    Public Overrides Function GetStandardValues(ByVal context As ITypeDescriptorContext) As StandardValuesCollection
        Dim svc = New CategoryService()
        Return New StandardValuesCollection(svc.GetAll().ToList())
    End Function
    Public Overrides Function GetStandardValuesSupported(ByVal context As ITypeDescriptorContext) As Boolean
        Return True
    End Function
    Public Overrides Function GetStandardValuesExclusive(ByVal context As ITypeDescriptorContext) As Boolean
        Return True
    End Function
    Public Overrides Function CanConvertFrom(ByVal context As ITypeDescriptorContext, ByVal sourceType As Type) As Boolean
        If sourceType = GetType(String) Then Return True
        Return MyBase.CanConvertFrom(context, sourceType)
    End Function
    Public Overrides Function ConvertFrom(context As ITypeDescriptorContext, culture As CultureInfo, value As Object) As Object
        If value IsNot Nothing AndAlso value.[GetType]() = GetType(String) Then
            Dim v = $"{value}"
            Dim id = Integer.Parse(v.Split("-"c)(0).Trim())
            Dim svc = New CategoryService()
            Return svc.GetAll().Where(Function(x) x.Id = id).FirstOrDefault()
        End If
        Return MyBase.ConvertFrom(context, culture, value)
    End Function
End Class

结果，当您设置ProductasSelectedObject的PropertyGrid, forCategory属性的实例时，您从列表中选择一个值。

示例 - C#

这是上述示例的 C# 版本：

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    [TypeConverter(typeof(CategoryConverter))]
    public Category Category { get; set; }
}
public class Category
{
    public int Id { get; set; }
    public string Name { get; set; }
    public override string ToString()
    {
        return $"{Id} - {Name}";
    }
}

public class CategoryService
{
    List<Category> list = new List<Category>{
        new Category() { Id = 1, Name = "Category 1" },
        new Category() { Id = 2, Name = "Category 2" },
        new Category() { Id = 3, Name = "Category 3" },
    };
    public IEnumerable<Category> GetAll()
    {
        return list;
    }
}

public class CategoryConverter : TypeConverter
{
    public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
    {
        var svc = new CategoryService();
        return new StandardValuesCollection(svc.GetAll().ToList());
    }
    public override bool GetStandardValuesSupported(ITypeDescriptorContext context)
    {
        return true;
    }
    public override bool GetStandardValuesExclusive(ITypeDescriptorContext context)
    {
        return true;
    }
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        if (sourceType == typeof(string))
            return true;
        return base.CanConvertFrom(context, sourceType);
    }
    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        if (value != null && value.GetType() == typeof(string))
        {
            var v = $"{value}";
            var id = int.Parse(v.Split('-')[0].Trim());
            var svc = new CategoryService();
            return svc.GetAll().Where(x => x.Id == id).FirstOrDefault();
        }
        return base.ConvertFrom(context, culture, value);
    }
}