通过反射设置属性时的类型转换问题 [英] Type conversion issue when setting property through reflection

问题描述

我们有一个类型为 long？的属性，其中填充了 int 。

We have a property of type long? that gets filled with an int.

当我直接将属性设置为 obj.Value = v; 时，此方法很好，但是当我尝试通过反射<$设置属性时c $ c> info.SetValue（obj，v，null）; 它给了我一个以下异常：

This works fine when i just set the property directly obj.Value = v; but when i try and set the property through reflection info.SetValue(obj, v, null); it gives me a the following exception:

类型'System.Int32'的对象不能转换为类型'System.Nullable`1 [System.Int64]'。

Object of type 'System.Int32' cannot be converted to type 'System.Nullable`1[System.Int64]'.

这是一个简化的场景：

    class TestClass
    {
        public long? Value { get; set; }
    }

    [TestMethod]
    public void TestMethod2()
    {
        TestClass obj = new TestClass();
        Type t = obj.GetType();

        PropertyInfo info = t.GetProperty("Value");
        int v = 1;

        // This works
        obj.Value = v;

        // This does not work
        info.SetValue(obj, v, null);
    }

为什么通过设置属性时不起作用反射在直接设置属性时有效吗？

Why does it not work when setting the property through reflection while it works when setting the property directly?

推荐答案

查看全文：如何使用反射来设置属性的值？

完整代码，如果您要为可空类型设置值

full code if you are setting value for nullable type

public static void SetValue(object inputObject, string propertyName, object propertyVal)
{
    //find out the type
    Type type = inputObject.GetType();

    //get the property information based on the type
    System.Reflection.PropertyInfo propertyInfo = type.GetProperty(propertyName);

    //find the property type
    Type propertyType = propertyInfo.PropertyType;

    //Convert.ChangeType does not handle conversion to nullable types
    //if the property type is nullable, we need to get the underlying type of the property
    var targetType = IsNullableType(propertyType) ? Nullable.GetUnderlyingType(propertyType) : propertyType;

    //Returns an System.Object with the specified System.Type and whose value is
    //equivalent to the specified object.
    propertyVal = Convert.ChangeType(propertyVal, targetType);

    //Set the value of the property
    propertyInfo.SetValue(inputObject, propertyVal, null);

}
private static bool IsNullableType(Type type)
{
    return type.IsGenericType && type.GetGenericTypeDefinition().Equals(typeof(Nullable<>));
}

---

您需要转换价值这样，即您需要将值转换为如下所示的属性类型

---

you need to convert value like this i.e you need to convert value to your property type like as below

PropertyInfo info = t.GetProperty("Value");
object value = null;
try 
{ 
    value = System.Convert.ChangeType(123, 
        Nullable.GetUnderlyingType(info.PropertyType));
} 
catch (InvalidCastException)
{
    return;
}
propertyInfo.SetValue(obj, value, null);

您需要执行此操作，因为您无法将任意值转换为给定类型...因此您需要像这样转换

you need to do this because you cannot convert any arbirtary value to given type...so you need to convert it like this

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