使用反射设置列表 <dynamic> 列出 <T>

Question

Say, I have these properties in a class :

public class Example
{
    public List<Toyota> listToyota; 
    public List<Honda> listHonda; 
    public List<Huyndai> listHuyndai; 
    ... 
    ... 
}

And there will be more properties if there are new car brands. Each brand is a table.

Normally, I would do this to get the data from tables :

Example result = new Example();
switch (brandname)
{
    case "Toyota":
        result.listToyota = * select table from context * ; 
        break;
    case "Honda":
        result.listHonda = * select table from context * ; 
        break;
        ...
}

Also, I'll have to add more code when there are new brands. I found this very annoying/time-consuming and decided to switch to a dynamic approach. I've sucessfully get the tables dynamically :

tblName = "Toyota"; 
IEnumerable<dynamic> table = typeof(MyContext).GetProperty(tblName).GetValue(context, null) as IEnumerable<dynamic>;

But I failed to dynamically set the property value, in this example, is listToyota :

query = (from a in table select a).ToList() as List<dynamic>;
SetPropertyValue(result, "listToyota", query);

I got this error :

Object of type 'System.Collections.Generic.List1[System.Object]' cannot be converted to type 'System.Collections.Generic.List1[Toyota]'.

SetPropertyValue is a very simple function using System.Reflection :

static void SetPropertyValue(object p, string propName, object value)
{
    Type t = p.GetType();

    System.Reflection.PropertyInfo info = t.GetProperty(propName);

    if (info == null)
        return;
    if (!info.CanWrite)
        return;
    info.SetValue(p, value, null);
}

Any advices are greatly appreciated!

Answer 1

Please try something like this

static void SetPropertyValue(object p, string propName, object value)
{
    Type t = p.GetType();

    System.Reflection.PropertyInfo info = t.GetProperty(propName);

    if (info == null)
        return;
    if (!info.CanWrite)
        return;

    var elemtype = info.PropertyType.GetElementType();
    var castmethod = typeof(Enumerable).GetMethod("Cast", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(elemtype);
    var tolist = typeof(Enumerable).GetMethod("ToList", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(elemtype);

    var collection = castmethod.Invoke(null, new object[] { value });
    var list = tolist.Invoke(null, new object[] { collection });

    info.SetValue(p, list, null);
}

Answer 2

I think the main problem is your software design. I wouldn't use dynamic this way.

1. I would create a Brand-Class. If you want to use dynamic, try something like this:

    public class DynamicBrand : DynamicObject { private IDictionary<string, object> myDynamicValues; public DynamicBrand() : base() { myDynamicValues = new Dictionary<string, object>(); } public void AddMember(string Name, object Value) { if (!myDynamicValues.ContainsKey(Name.Trim().ToLower())) { myDynamicValues.Add(Name.ToLower().Trim(), Value); } else { throw new Exception("The Member with the Name: " + Name + " already exists!"); } } public override bool TrySetMember(SetMemberBinder Binder, object Value) { if (myDynamicValues.ContainsKey(Binder.Name.ToLower())) { myDynamicValues[Binder.Name.ToLower()] = Value; return true; } else { myDynamicValues.Add(Binder.Name.ToLower(), Value); } return true; } publc override bool TryGetMember(GetMemberBinder Binder, out object Result) { if (myDynamicValues.ContainsKey(Binder.Name.ToLower())) { Result = myDynamicValues[Binder.Name.ToLower()]; return true; } else { Result = null; return false; } } 

2. I would change your example class

    public class Example { // string = brand-name; list = list of dynamic brand items public Dictionary<string, List<DynamicBrand>> brands; } 

3. Whenyou fill your data, just add a new dynamic brand to your brands-list and simply add the member you need.

EDIT : Dynamic isn't a very nice solution for your problem. I would think about a completly different structure.