Question

我有一个词典：

Dictionary<int, Type> AllDrillTypes = new Dictionary<int, Type>()
{
  {13,typeof(TCHEMISTRY)},
  {14,typeof(TDRILLSPAN)}
};

其中TCHEMISTRY和TDRILLSPAN是类。然后我想从这些类中获取行，如下所示：

Type T = AllDrillTypes[13];
var LC = Activator.CreateInstance( typeof(List<>).MakeGenericType( T ) );
MethodInfo M = T.GetMethod("FindAll", BindingFlags.Public | BindingFlags.Static, null, new Type[] { }, null);    
LC = M.Invoke(null, new object[] { });

所有这些代码都能正常运行。之后我需要得到这样的行：

var LingLC = from obj in LC where obj.RunID == 1001 select obj;

但这一行会导致错误：

“无法找到源类型的查询模式的实现 '宾语'。 “哪里找不到。”

此代码行出了什么问题？

Answer 1

即使您无法更改类定义，也可以避免使用反射：

// Getter dictionary rather than type dictionary.
Dictionary<int, Func<IEnumerable<object>>> DrillTypeGetters =
    new Dictionary<int, Func<IEnumerable<object>>>()   
    {  
        { 13, () => TCHEMISTRY.FindAll().Cast<object>() },
        { 14, () => TDRILLSPAN.FindAll().Cast<object>() }
    };
Dictionary<int, Func<object, int>> IDGetters =
    new Dictionary<int, Func<object, int>>()
    {
        { 13, o => ((TCHEMISTRY)o).RunID },
        { 14, o => ((TDRILLSPAN)o).RunID }
    };

IEnumerable<object> LC = DrillTypeGetters[13]();
IEnumerable<object> LingLC = 
    from obj in LC
    where IDGetters[13](obj) == 1001
    select obj;

或者您甚至可以启用13 / 14并为每种类型运行完全不同的方法。

if (choice == 13)
    IEnumerable<TCHEMISTRY> LingLC =
        TCHEMISTRY.FindAll().Where(tc => tc.RunID == 1001);
else if (choice == 14)
    IEnumerable<TDRILLSPAN> LingLC =
        TDRILLSPAN.FindAll().Where(td => td.RunID == 1001);

基本上，如果这两个类不共享任何公共层次结构，则不能编写任何公共代码来处理它们。如果他们有很多相似的属性，你可以像我在第一个例子中那样使用getter来提供一种获取类似属性的方法，无论你正在处理什么类型的类。如果他们甚至没有类似的属性，请不要尝试编写共享代码。

Answer 2

也许你可以将你的代码改写成这样的东西，......以获得更加类型安全的解决方案（不使用反射）。

void Main()
{
    var driller1 = new DrillerWhichYouCannotChange1();
    var driller2 = new DrillerWhichYouCannotChange2();

    var allDrillTypes = new Dictionary<int, IList<IDriller>>()
    {
        { 13, new List<IDriller>() { new DrillerWhichYouCannotChange1Adapter(driller1) } },
        { 14, new List<IDriller>() { new DrillerWhichYouCannotChange2Adapter(driller2) } },
    };

    Console.WriteLine(allDrillTypes[13][0].SomeCommonProperty); // prints 123
    Console.WriteLine(allDrillTypes[14][0].SomeCommonProperty); // prints 456
}

interface IDriller
{
    int SomeCommonProperty { get; }
}

class DrillerWhichYouCannotChange1Adapter : IDriller
{
    private DrillerWhichYouCannotChange1 inner;

    public DrillerWhichYouCannotChange1Adapter(DrillerWhichYouCannotChange1 inner)
    {
        this.inner = inner;
    }

    public int SomeCommonProperty { get { return this.inner.PropertyX; } }
}

class DrillerWhichYouCannotChange2Adapter : IDriller
{
    private DrillerWhichYouCannotChange2 inner;

    public DrillerWhichYouCannotChange2Adapter(DrillerWhichYouCannotChange2 inner)
    {
        this.inner = inner;
    }

    public int SomeCommonProperty { get { return this.inner.PropertyY; } }
}

class DrillerWhichYouCannotChange1
{
    public int PropertyX { get { return 123; } }
}

class DrillerWhichYouCannotChange2
{
    public int PropertyY { get { return 456; } }
}

编辑：如果您无法更改司钻类，则可以使用适配器模式为每个司机创建一个适配器，该适配器实现IDiller。

Answer 3

您需要将LC转换为FindAll方法的返回类型。有点像：

var genericList = ((List<TChemistry>) LC);
var LingLC = from obj in genericList where obj.RunID == 1001 select obj;

这假设FindAll返回一个TChemistry的集合。

- 修改

如果您在运行时不知道类型是TChemistry还是TDrillspan，那么您必须编写if / else of switch语句以转换为正确的类型。我宁愿让TChemistry和TDrillSpan扩展一个抽象类或接口，你只需要转换为List，你将永远拥有RunId属性。

public abstract class TAbstract
{
   public abstract int RunId {get; set;}
}

public class TChemistry : TAbstract
{
    public override int RunId {get; set;}
}

public class TDrillSpan : TAbstract
{
   public override int RunId {get; set;}
}

Type T = AllDrillTypes[13] as TAbstract;
var LC = Activator.CreateInstance( typeof(List<>).MakeGenericType( T ) );
MethodInfo M = T.GetMethod("FindAll", BindingFlags.Public | BindingFlags.Static, null, new Type[] { }, null);    
LC = M.Invoke(null, new object[] { });

var genericList = ((List<TAbstract>) LC);
var LingLC = from obj in genericList where obj.RunID == 1001 select obj;

如果你不能改变类的声明，那么你只会留下丑陋的if else：

var typeInfo = LC.GetType();
IEnumerable<T> genericList;
if (typeInfo == typeof(IEnumerable<TChemistry>)
{
    genericList = (List<TChemistry>) LC;
)
else if (typeInfo == typeof(IEnumerable<TDrillSpan>)
{
    genericList = (List<TDrillSpan>) LC;
}

var LingLC = from obj in genericList where obj.RunID == 1001 select obj;

Answer 4

尝试

IEnumerable returnedObjects = (IEnumerable)M.Invoke(null, new object[] { }) as IEnumerable;

然后遍历你的可数字

foreach (object report in returnedObjects)
{
    // Use reflection to read properties or add to a new List<object> if you
    // need an ICollection<object>
}

而不是：

LC = M.Invoke(null, new object[] { });

如何使用linq从var-source获取值

4 个答案: