获取类成员的默认值

发布于 2024-09-04 04:32:06 字数 219 浏览 4 评论 0原文

假设我有一个 ClassWithMember 类，

class ClassWithMember
{
    int myIntMember = 10;
}

如何通过 System.Type 获取 myIntMember 成员的默认值 10？

我目前正在努力解决所有我检索到的反射，即 int (0) 的默认值而不是类默认成员 (10) ..

原文

Let's assume I have a class ClassWithMember

class ClassWithMember
{
    int myIntMember = 10;
}

How do I get the default value 10 of the myIntMember member by System.Type?

I'm currently struggling around with reflections by all I retreive is the default value of int (0) not the classes default member (10)..

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烦人精 2024-09-11 04:32:06

您可以尝试这样的事情：

var field = typeof(ClassWithMember).GetField("myIntMember",
    BindingFlags.Instance | BindingFlags.NonPublic);
var value = (int)field.GetValue(new ClassWithMember());

这里的技巧是实例化一个实例。

You can try something like this:

var field = typeof(ClassWithMember).GetField("myIntMember",
    BindingFlags.Instance | BindingFlags.NonPublic);
var value = (int)field.GetValue(new ClassWithMember());

The trick here is to instantiate an instance.

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背叛残局 2024-09-11 04:32:06

尝试创建一个实例并通过反射检索值。

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盗琴音 2024-09-11 04:32:06

如果您控制 ClassWithMember 的代码，则可以使用 System.ComponentModel 中的 [DefaultValue] 属性，采取完全不同的方法。基本上，您要做的就是编写如下内容：

class ClassWithMember
{
    public ClassWithMember()
    {
        SetDefaultValues();
    }

    [DefaultValue(5)]
    public MyIntMember { get; set; }
}

然后在某处（也许在基类中）有一个类似的函数：

public void SetDefaultValues()
{
    foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(this))
    {
        DefaultValueAttribute a = prop.Attributes[typeof(DefaultValueAttribute)] as DefaultValueAttribute;
        if (a == null) 
            continue;
        prop.SetValue(this, a.Value);
    }
}

所以现在，您可以使用反射轻松检索默认值。

请记住，由于反射要求，这会慢很多，因此如果此代码被实例化很多，您可能需要找到一种不同的方法。此外，由于 .NET Framework 属性支持的限制，它不适用于非值类型。

If you're in control of the code for ClassWithMember, you could take a completely different approach to this by using the [DefaultValue] attribute from System.ComponentModel. Basically, what you'd do is write something like this:

class ClassWithMember
{
    public ClassWithMember()
    {
        SetDefaultValues();
    }

    [DefaultValue(5)]
    public MyIntMember { get; set; }
}

And then have a function like this somewhere, perhaps in a base class:

public void SetDefaultValues()
{
    foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(this))
    {
        DefaultValueAttribute a = prop.Attributes[typeof(DefaultValueAttribute)] as DefaultValueAttribute;
        if (a == null) 
            continue;
        prop.SetValue(this, a.Value);
    }
}

So now, you have a situation where you can easily retrieve the default values using Reflection.

Keep in mind that this is going to be quite a lot slower due to the Reflection requirement, so if this code gets instantiated a lot, you'll probably want to find a different approach. Also, it won't work with non-value types, due to a limitation with the .NET Framework's attribute support.

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