如何动态地将基类型的列表强制转换为派生类型

本文关键字：类型 列表 转换 派生 基类 何动态 动态 | 更新日期: 2023-09-27 17:55:02

我有一个dll与以下层次结构:

Interface ISchema {}
class Schema:ISchema{}
class TableSchema:Schema{}
class ViewSchema:Schema{}

我有另一个具有以下层次结构的dll:

Interface ISearch {}
class Table:ISearch{}
class View:ISearch{}

以下代码根据用户选择触发对Table或View的搜索操作:

private void FindNowButton_Click(object sender, EventArgs e)
{
    // return Table or View according to user selection. (Property is an internal class helping to retrieve the selected type)
    var type = (ObjectsTypeComboBox.SelectedItem as Property).Type;
    // Create an instance of table or View as ISearch
    var instance = (ISearch)Activator.CreateInstance(type);
    // Call to relevant Search (table.Search or View.Search)
    // _dataManager help to get the records from Schema hierarchy
    // text is the text to search
    var result = instance.Search(_dataManager, FindWhatTextBox.Text);
    // Show in DataGridView the result
    FindResultsDGV.DataSource = result;
}

每个搜索方法返回一个List。我需要在网格上显示不同的列。TableSchema和ViewSchema有不同的属性，按照下面的方式进行转换。

FindResultsDGV.DataSource = result.Cast<TableSchema> ; // or result.Cast<ViewSchema>

我如何在这个阶段动态地获得正确的类型?

欢迎任何其他解决方案

更新:

根据@GiladGreen

public interface ISearchSchemaFactory
{
    ISearch<ISchema> GetSearch(Type schemaType);
}
public class Factory : ISearchSchemaFactory
{
    public ISearch<ISchema> GetSearch(Type schemaType)
    {
        if (schemaType.Equals(typeof(Table)))
        {
            return new BL.AdvancedSearch.Table(); // Getting an error here
           // Cannot implicitly convert type 'Table' to 'ISearch<ISchema>'. An explicit conversion exists (are you missing a cast?) 
        }
        else if (schemaType.Equals(typeof(View)))
        {
            // TODO
        }
        return null; // TODO
    }
}

如何动态地将基类型的列表强制转换为派生类型

我建议你这样修改ISearch:

Interface ISearch<out TSchema> where TSchema: ISchema
{
    TSchema Search(....);   
}
class Table : ISearch<TableSchema>
{
    public TableSchema Search(....)
    {
        //Some searching code
    }
}
class View:ISearch<ViewSchema>
{
    public ViewSchema Search(....)
    {
        //Some searching code
    }
}

然后你还可以做的是有一个ISearchSchemaFactory，它会根据你给它的TSchema给你一个正确的ISearch的实例:

public interface ISearchSchemaFactory
{
    ISearch<ISchema> GetSearch(Type schemaType);
}

和用法:var search = factory.GetSearch(type);

Factoy实现示例

public class MappingSearchSchemaFactory : ISearchSchemaFactory
{
    public MappingSearchSchemaFactory(Dictionary<Type, ISearch<ISchema>> mapping)
    {
        Mapping = mapping;
    }
    ISearch<ISchema> GetSearch(Type schemaType)
    {
        ISearch<ISchema> result;
        if(!Mapping.TryGetValue(schemaType, out result)
        {
            //Some logging or throwing exception behavior - depends what you want
        }
        return result;
    }
    public Dictionary<Type, ISearch<ISchema>> Mapping { get; set; }
}

这个特定的实现为"某人"获取映射。一个可能的初始化代码可以是:

ISearchSchemaFactory factory = new MappingSearchSchemaFactory(
    new Dictionary<Type,ISearch<ISchema>>
    { new TableSchema(), new Table() },
    { new ViewSchema(), new view() }
);

但是我不太推荐这个。我会查看Dependency Injection和IoC Containers来管理对象的初始化。我个人使用Castle Windsor

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