c# - 代码契约(Contract)不检查空条件。为什么？

Question

为什么 .NET Contracts 不提示这段代码？

private static User GetUser()
{
    var sFirstName = Console.ReadLine();
    var sLastName = Console.ReadLine();
    if (sLastName == "NULL")
    {
        return null;
    }
    else
    {
        return new User(sLastName, sFirstName);
    }
}
public static int Main(string[] args)
{
        var oUser = GetUser();
        DisplayUser(oUser);
        Console.ReadLine();
        return 0;
}
private static void DisplayUser(User user)
{
    Contract.Requires(user != null);
    Console.WriteLine(user.ToString());
}

GetUser 可以返回 null，但契约(Contract)从未规定我必须在将返回值传递给 DisplayUser 之前检查返回值。为什么？

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AutoAnswer:代码契约配置中存在警告级别。我应该把它从低到高。

Answer 1

根据 this msdn页面，如果您没有在 Visual Studio 中安装正确的插件，契约(Contract)将不会被执行。你安装那个插件了吗？

You must install a Visual Studio add-in to enforce contracts. The Code Contracts Premium Edition add-in lets you specify static and run-time checking of code contracts on the project Properties page. If you do not enable run-time checking, contracts such as the Contract.Ensures method will not throw exceptions during run time if a contract is violated. The Visual Studio add-in does not ship with Visual Studio 2010 or the Windows SDK.