Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
505 views
in Technique[技术] by (71.8m points)

c# - How to provide conversion when using Reflection.SetValue?

I have a class that pretends to be an int, so it has overloaded the various operators;

public class MyId
{
    int value;
    public virtual int Value
    {
        get { return this.value; }
        set { this.value = value; }
    }

    public MyId(int value)
    {
        this.value = value;
    }


    public static implicit operator MyId(int rhs)
    {
        return new MyId(rhs);
    }

    public static implicit operator int(MyId rhs)
    {
        return rhs.Value;
    }


}

However, when I use code like

PropertyInfo.SetValue(myObj, 13, null)
OR
MyId myId = 13;
int x = Convert.ToInt32(myId);
IConvertible iConvertible = x as IConvertible;
iConvertible.ToType(typeof(MyId), CultureInfo.CurrentCulture);

I get invalid cast. I'm puzzled, both calls seem to attempt to call convert on the int which will fail because int doesn't understand the type MyId (even though all the assignment operators are there). Any ideas of a workaround for this, I'm sure I must be missing something stupid?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

Implicit conversions are a C# construct and are not available through reflection. Additionally, setting a field or property through reflection means that you must provide the appropriate type up front. You can attempt to circumvent this by using a custom TypeConverter (or some other means of custom conversion) to help convert your types at runtime prior to using reflection. Here's a rough example of a TypeConverter implementation.

public class MyIdTypeConverter : TypeConverter
{                
    public override object ConvertFrom(ITypeDescriptorContext context,
                                       System.Globalization.CultureInfo culture,
                                       object value)
    {   
        if (value is int)
            return new MyId((int)value);
        else if (value is MyId)
            return value;
        return base.ConvertFrom(context, culture, value);
    }               
}

Here's the type that we would be trying to set the Custom property on.

public class Container
{
    [TypeConverter(typeof(MyIdTypeConverter))]
    public MyId Custom { get; set; }                
}

The code to call it would have to check the attribute and perform the conversion ahead of time, after which it could call SetValue.

var instance = new Container();
var type = typeof(Container);
var property = type.GetProperty("Custom");

var descriptor = TypeDescriptor.GetProperties(instance)["Custom"];
var converter = descriptor.Converter;                
property.SetValue(instance, converter.ConvertFrom(15), null);

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...