C# - 使用反射设置属性

Question

SO Community,

So I'm learning C# and am still trying to wrap my head around reflection. In particular trying to use it to access a property of a property on a class.

I've boiled down the basic task that I'm trying to accomplish below:

public enum SIGNAL_STATE { NOT_RETRIEVED = 0, RETRIEVING = 1, RETRIEVED = 2, FAILED = 3 }

public class MyObjectClass
{
    public string MyString;
    private SIGNAL_STATE _state = SIGNAL_STATE.NOT_RETRIEVED;
    public SIGNAL_STATE State { get { return _state; } set { _state = value;} }
}

public class NeedToReflect
{
    private MyObjectClass _myObject1 = new MyObjectClass();
    private MyObjectClass _myObject2 = new MyObjectClass();
    private MyObjectClass _myObject3 = new MyObjectClass();

    public MyObjectClass MyObject1
    {
        get{return _myObject1;} 
        set{_myObject1 = value;}
    }

    public MyObjectClass MyObject2
    {
        get{return _myObject2;}
        set{_myObject2 = value;}
    }

    public MyObjectClass MyObject3
    {
        get{return _myObject3;}
        set{_myObject3 = value;}
    }

    public static void Main(string [] args){
        NeedToReflect needToReflect = new NeedToReflect();

        string fieldName;
        for(int idx = 1; idx<=3; ++idx)
        {
            fieldName = String.Format("MyObject{0}",idx);

            //TODO: set state of 'MyObject' values to SIGNAL_STATE.RETRIEVING

        }
    }
}

edit 1 :

At Yair Nevet's suggestion I'm grabbing the FieldInfo from the applicable object like,

FieldInfo fieldInfo = needToReflect.GetType().GetField(fieldName, BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance);

But from there I get hung up on accessing and setting the right 'State' Field/Property on that member field

Solution (ie. here's what I plugged in on that TODO comment):

// Determine what binding flags will give us proper access to our member field
BindingFlags bindFlags = BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance;
// Get the field for that field
FieldInfo fieldInfo = needToReflect.GetType().GetField(fieldName, bindFlags);
// Pass in the containing object that we're reflecting on to get an instance of the member field
MyObjectClass myField = (MyObjectClass) fieldInfo.GetValue(needToReflect);
// We can now directly access and edit the value in question
myField.State = SIGNAL_STATE.RETRIEVING;

That does it. Thanks to Shlomi Borovitz for pointing me in the right direction.

Thanks!

Answer 1

You are trying to access a Property while the member is actually a private Field :

propertyName = String.Format("MyObject{0}",idx);

Use GetField method instead for that:

needToReflect.GetType().GetField(propertyName, BindingFlags.NonPublic |BindingFlags.GetField | BindingFlags.Instance);

Answer 2

The FieldInfo object which returned by GetField has property which called FieldInfo , which returns the type of that field. And you can query it for that type's (the type of the field) properties/fields (and whatever you want) - and get/set them.

Remember that both GetType method (of any object), and the FieldInfo.FieldType property return Type object, that you can query in reflection.

object obj =... 
var field = obj.GetType().GetField(fieldName,...);
field.FieldType.GetField(... 
//etc... etc... 

For each field, you can query the type and for each type, you can query the fields, and get/set them.

BTW, in C# 4.0 you can use the dynamic pseudo type (it used as a type when declaring dynamic variable, but it's not a real type), and then using that variable, while assuming which properties/fields/methods that variable would have in runtime (ie, using them like they are known in compile time although they don't). This will not work for private members (and I can't warn you enough against calling private members in reflection), but for public members, this would make your code simple and readable, like you never used reflection (although, behind the scenes [in this case] reflection would be used).

Answer 3

完成这些步骤...

1) Get the Type.
2) Have an instance of that type.
3) Get the PropertyInfo for the property.
4) Call "GetSetMethod" on the PropertyInfo object. It will return a MethodInfo object.
5) Invoke the MethodInfo object using the instance of the type and a value.

Answer 4

Given:

class ClassyMcClass
{
    public int PropertyB { get; set; }
}

class MyClass
{
    public ClassyMcClass PropertyA { get; set; }
}

The following code uses reflection on a MyClass object to set the int value of PropertyB in PropertyA to NewValue :

PropertyInfo propA = typeof(MyClass).GetProperty("PropertyA");
PropertyInfo probBofA = propA.PropertyType.GetProperty("PropertyB");

// Set property B of property A, where obj is of type MyClass
probBofA.SetValue(propA.GetValue(obj), NewValue, null);