如何从反射执行显式操作转换? [英] How do I perform explicit operation casting from reflection?

问题描述

我想使用反射，并使用反射进行隐式或显式掩盖.

鉴于我以这种方式定义了Foo

public class Foo
{
    public static explicit operator decimal(Foo foo)
    {
        return foo.Value;
    }

    public static explicit operator Foo(decimal number)
    {
        return new Foo(number);
    }

    public Foo() { }

    public Foo(decimal number)
    {
        Value = number;
    }

    public decimal Value { get; set; }

    public override string ToString()
    {
        return Value.ToString();
    }
}

当我运行这段代码时

decimal someNumber = 42.42m;

var test = (Foo)someNumber;

Console.WriteLine(test);        // Writes 42.42 No problems

当我尝试使用Foo作为成员类型定义一个类并使用反射对其进行设置时.我收到以下异常.

Error     : Object of type 'System.Decimal' cannot be converted to type 'Foo'.
StackTrace:    at System.RuntimeType.TryChangeType(Object value, Binder binder, CultureInfo culture, Boolean needsSpecialCast)
               at System.RuntimeType.CheckValue(Object value, Binder binder, CultureInfo culture, BindingFlags invokeAttr)
               at System.Reflection.MethodBase.CheckArguments(Object[] parameters, Binder binder, BindingFlags invokeAttr, CultureInfo culture, Signature sig)
               at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
               at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
               at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
               at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, Object[] index)

这是我用来设置反射属性的代码

public class FooComposite
{
    public Foo Bar { get; set; }
}

var properties = typeof(FooComposite).GetProperties();

var testFoo = new FooComposite();

foreach(var propertyInfo in properties)
{
    propertyInfo.SetValue(testFoo, 17.17m, null);  // Exception generated on this line
}

Console.WriteLine(testFoo.Bar);  // Never gets here

我该如何进行转换?

解决方案

与非反射代码的确没有什么不同，您仍然需要将数字显式转换为Foo:

propertyInfo.SetValue(testFoo,(Foo)17.17m, null);

实时示例: http://rextester.com/rundotnet?code=BPQ74480

出于兴趣我尝试了几种选择.

1. 将其设为Foo中的implicit强制转换-无效，出现相同的错误 ^实时
2. 使用Convert.ChangeType(17.17m,typeof(Foo))-也不起作用. ^实时

I want to use reflection and do either an implicit or explicit coversion using reflection.

Given I have defined Foo this way

public class Foo
{
    public static explicit operator decimal(Foo foo)
    {
        return foo.Value;
    }

    public static explicit operator Foo(decimal number)
    {
        return new Foo(number);
    }

    public Foo() { }

    public Foo(decimal number)
    {
        Value = number;
    }

    public decimal Value { get; set; }

    public override string ToString()
    {
        return Value.ToString();
    }
}

When I run this code

decimal someNumber = 42.42m;

var test = (Foo)someNumber;

Console.WriteLine(test);        // Writes 42.42 No problems

When I try to define a class with Foo as a member type and use reflection to set it. I get the following Exception.

Error     : Object of type 'System.Decimal' cannot be converted to type 'Foo'.
StackTrace:    at System.RuntimeType.TryChangeType(Object value, Binder binder, CultureInfo culture, Boolean needsSpecialCast)
               at System.RuntimeType.CheckValue(Object value, Binder binder, CultureInfo culture, BindingFlags invokeAttr)
               at System.Reflection.MethodBase.CheckArguments(Object[] parameters, Binder binder, BindingFlags invokeAttr, CultureInfo culture, Signature sig)
               at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
               at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
               at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
               at System.Reflection.RuntimePropertyInfo.SetValue(Object obj, Object value, Object[] index)

Here is the code I use to set the property with reflection

public class FooComposite
{
    public Foo Bar { get; set; }
}

var properties = typeof(FooComposite).GetProperties();

var testFoo = new FooComposite();

foreach(var propertyInfo in properties)
{
    propertyInfo.SetValue(testFoo, 17.17m, null);  // Exception generated on this line
}

Console.WriteLine(testFoo.Bar);  // Never gets here

How can I do this conversion?

解决方案

Well its really no different from your non-reflection code, you still need to explicitly cast the number to a Foo:

propertyInfo.SetValue(testFoo,(Foo)17.17m, null);

Live example: http://rextester.com/rundotnet?code=BPQ74480

Out of interest I tried a few alternatives.

1. Make it an implicit cast in Foo - doesnt work, same error ^Live
2. Use Convert.ChangeType(17.17m,typeof(Foo)) - also doesnt work. ^Live

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