c# - Nullable.GetUnderlyingType 无法正常工作

Question

我有以下代码:

Tuple<string, string, Type, ParameterInfo[]> method = (Tuple<string, string, Type, ParameterInfo[]>)(comboBox1.SelectedItem);
if (comboBox2.SelectedIndex - 1 >= 0)
{
    if (method.Item4[comboBox2.SelectedIndex - 1].ParameterType.BaseType == typeof(Enum))
    {
        foreach (object type in Enum.GetValues(method.Item4[comboBox2.SelectedIndex - 1].ParameterType))
        {
            Console.WriteLine(type);
        }
        MessageBox.Show("This looks like an auto-generated type; you shouldn't set it to anything.", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning, MessageBoxDefaultButton.Button1);
    }
    else if (Nullable.GetUnderlyingType(method.Item4[comboBox2.SelectedIndex - 1].ParameterType) != null)
    {
        if (Nullable.GetUnderlyingType(method.Item4[comboBox2.SelectedIndex - 1].ParameterType).BaseType == typeof(Enum))
        {
            MessageBox.Show("This looks like an auto-generated type; you shouldn't set it to anything.", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning, MessageBoxDefaultButton.Button1);
        }
    }
}

在 else if 语句中，我注意到它总是返回 null，即使在我的例子中 method.Item4[0] 处的对象在 comboBox2.SelectedIndex 为 1 时始终是 Nullable 类型，那么为什么它返回 null ？说真的，我在那里放了一个断点，在 Item4 中，我看到索引 0 处的对象为:

[0] = {System.Nullable`1[CarConditionEnum]& carCondition}

...在索引 1 处为:

[1] = {Boolean& carConditionSpecified}

Answer 1

问题是参数是引用类型，即它被声明为 ref CarConditionEnum？参数名.

需要获取参数的元素类型，然后使用Nullable.GetUnderlyingType:

Type paramType = method.Item4[comboBox2.SelectedIndex - 1].ParameterType;
if(paramType.HasElementType)
{
    paramType = paramType.GetElementType();
}

if(Nullable.GetUnderlyingType(paramType) != null)
{
}