在运行时添加属性 [英] Add properties at runtime

问题描述

我有一个类，程序员可以使用它来动态添加新属性.为此，它实现了 ICustomTypeDescriptor 以能够覆盖 GetProperties() 方法.

I have a class which the programmer can use to dynamically add new properties. For that it implements the ICustomTypeDescriptor to be able to override GetProperties() method.

public class DynamicProperty
{
    public object Value { get; set; }

    public Type Type { get; set; }

    public string Name { get; set; }

    public Collection<Attribute> Attributes { get; set; }
}

public class DynamicClass : ICustomTypeDescriptor
{
    // Collection to code add dynamic properties
    public KeyedCollection<string, DynamicProperty> Properties
    {
        get;
        private set;
    }

    // ICustomTypeDescriptor implementation
    PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties()
    {
        // Properties founded within instance
        PropertyInfo[] instanceProps = this.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance);

        // Fill property collection with founded properties
        PropertyDescriptorCollection propsCollection = 
            new PropertyDescriptorCollection(instanceProps.Cast<PropertyDescriptor>().ToArray());

        // Fill property collection with dynamic properties (Properties)
        foreach (var prop in Properties)
        {
            // HOW TO?
        }

        return propsCollection;
    }
}

是否可以遍历 Properties 列表以将每个属性添加到 PropertyDescriptorCollection?

Is it possible to iterate over the Properties list to add each property to PropertyDescriptorCollection?

基本上我希望程序员能够将 DynamicProperty 添加到将由 GetProperties 处理的集合中.类似的东西:

Basically I want the programmer to be able to add a DynamicProperty to a collection which will be handled by GetProperties. Something like:

new DynamicClass()
{
    Properties = {
        new DynamicProperty() {
            Name = "StringProp",
            Type = System.String,
            Value = "My string here"
        },

        new DynamicProperty() {
            Name = "IntProp",
            Type = System.Int32,
            Value = 10
        }
    }
}

现在，每当调用 GetProperties 时，这些 Properties 将被设置为实例属性.我的想法正确吗?

Now those Properties would be setted to instance properties whenever GetPropertiesis called. Am I thinking this the right way?

推荐答案

您已经在创建这样的集合:

You are already creating a collection like this:

PropertyDescriptorCollection propsCollection = 
            new PropertyDescriptorCollection(instanceProps.Cast<PropertyDescriptor>().ToArray());

但是您创建的集合只有现有的属性，没有您的新属性.

But the collection you are creating only has the existing properties, not your new properties.

您需要提供一个由现有属性和新属性串联而成的数组.

You need to supply a single array concatenated from the existing properties and your new properties.

像这样:

instanceProps.Cast<PropertyDescriptor>().Concat(customProperties).ToArray()

下一个问题:您需要customProperties，它是PropertyDescriptor 的集合.不幸的是，PropertyDescriptor 是一个抽象类，因此您没有一种简单的方法来创建它.

Next problem: you need customProperties which is a collection of PropertyDescriptor. Unfortunately PropertyDescriptor is an abstract class so you don't have an easy way to create one.

我们可以解决这个问题，只需通过从 PropertyDescriptor 派生并实现所有抽象方法来定义您自己的 CustomPropertyDescriptor 类.

We can fix this though, just define your own CustomPropertyDescriptor class by deriving from PropertyDescriptor and implementing all the abstract methods.

像这样:

public class CustomPropertyDescriptor : PropertyDescriptor
{
    private Type propertyType;
    private Type componentType;

    public CustomPropertyDescriptor(string propertyName, Type propertyType, Type componentType)
        : base(propertyName, new Attribute[] { })
    {
        this.propertyType = propertyType;
        this.componentType = componentType;
    }

    public override bool CanResetValue(object component) { return true; }
    public override Type ComponentType { get { return componentType; } }
    public override object GetValue(object component) { return 0; /* your code here to get a value */; }
    public override bool IsReadOnly { get { return false; } }
    public override Type PropertyType { get { return propertyType; } }
    public override void ResetValue(object component) { SetValue(component, null); }
    public override void SetValue(object component, object value) { /* your code here to set a value */; }
    public override bool ShouldSerializeValue(object component) { return true; }
}

我还没有填写获取和设置属性的调用；这些调用取决于您如何在幕后实现动态属性.

I haven't filled in the calls to get and set your properties; those calls depend on how you've implemented the dynamic properties under the hood.

然后，您需要创建一个 CustomPropertyDescriptor 数组，其中填充了适合您的动态属性的信息，并将其连接到我最初描述的基本属性.

Then you need to create an array of CustomPropertyDescriptor filled in with information appropriate to your dynamic properties, and concatenate it to the basic properties as I described initially.

PropertyDescriptor 不仅描述您的属性，它还使客户端能够实际获取和设置这些属性的值.这就是重点，不是吗！

The PropertyDescriptor not only describes your properties, it also enables client to actually get and set the values of those properties. And that's the whole point, isn't it!

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