测试 Convert.ChangeType 是否适用于两种类型

问题描述

这是关于使用反射转换值的这个问题的后续.可以像这样将某种类型的对象转换为另一种类型:

This is a follow-up to this question about converting values with reflection. Converting an object of a certain type to another type can be done like this:

object convertedValue = Convert.ChangeType(value, targetType);

给定两个 Type 实例(比如 FromType 和 ToType)，有没有办法测试转换是否成功?

Given two Type instances (say FromType and ToType), is there a way to test whether the conversion will succeed?

例如我可以编写这样的扩展方法吗:

E.g. can I write an extension method like this:

public static class TypeExtensions
{
    public static bool CanChangeType(this Type fromType, Type toType)
    {
        // what to put here?
    }
}

这就是我现在所拥有的.丑，但我还没有看到另一种方式......

This is what I have right now. Ugly, but I don't see another way yet...

bool CanChangeType(Type sourceType, Type targetType)
{
  try
  {
    var instanceOfSourceType = Activator.CreateInstance(sourceType);
    Convert.ChangeType(instanceOfSourceType, targetType);
    return true; // OK, it can be converted
  }
  catch (Exception ex)
  {
    return false;
  }

推荐答案

我刚刚遇到了同样的问题，我使用 Reflector 查看 ChangeType 的源代码.ChangeType 在 3 种情况下抛出异常:

I was just encountering this same issue, and I used Reflector to look at the source for ChangeType. ChangeType throws exceptions in 3 cases:

1. conversionType 为空
2. 值为空
3. 值未实现 IConvertible

这3个都勾选后，就保证可以转换了.因此，您只需自己检查这 3 件事，即可节省大量性能并移除 try{}/catch{} 块:

After those 3 are checked, it is guaranteed that it can be converted. So you can save a lot of performance and remove the try{}/catch{} block by simply checking those 3 things yourself:

public static bool CanChangeType(object value, Type conversionType)
{
    if (conversionType == null)
    {
        return false;
    }

    if (value == null)
    {
        return false;
    }

    IConvertible convertible = value as IConvertible;

    if (convertible == null)
    {
        return false;
    }

    return true;
}

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