DataGridView没有显示实现ICustomTypeDescriptor的对象的属性

Question

我在DataGridView中显示对象列表。一切都很顺利。列是根据对象的属性自动添加到DataGridView中的。

现在，我更改了在网格中显示的类，以实现ICustomTypeDescriptor.但是现在，当我将DataSource设置为自定义对象的列表时，网格现在不再显示任何列或行。

我猜想这与这样一个事实有关:使用ICustomTypeDescriptor，每个网格的每一行中显示的每个实例都可能返回不同的属性集。

我正在实现ICustomTypeDescriptor，以便允许用户在运行时动态地向对象添加自定义属性。这些自定义属性应该是可见的，可以通过DataGridView.编辑。

为什么DataGridView看不到我的ICustomTypeDescriptor方法？是否有另一种方法可以动态地向将显示在DataGridView中的对象添加属性？

Answer 1

DataGridView查看元数据的列表版本；其规则是.综合体：

1. 如果数据源实现IListSource，则计算GetList()作为数据源(在2处继续)，如果数据源实现ITypedList，则使用GetProperties()获取元数据(Exit)

H 110，如果可以找到一个类型化(非object)索引器(即public T this[int index])，则通过TypeDescriptor.GetProperties(type)：G 115H 116通过TypeDescriptionProvider使用D13作为源：G 115H 116它用于针对(exit)

1. otherwise反射类型的元数据，用于元数据(exit)

。

​

如果列表是非空的，则第一个对象用于通过(exit)实现TypeDescriptor.GetProperties(list[0])：

1. ，然后使用(退出)*
2. ，如果指定了TypeDescriptionProvider，则用于针对类型(exit) *H 233H 134的元数据，否则就使用反射。

​

1. 元数据不可用(退出)

(*=I不记得这两个人走哪条路.)

如果您使用的是List<T> (或类似的)，则会遇到“最简单”(IMO)的情况-- #3。如果您想提供自定义元数据，最好是编写一个TypeDescriptionProvider并将其与类型关联起来。我可以写一个例子，但它需要一段时间(在火车上，可能).

编辑：here's --一个使用ITypedList的示例；我将尝试将其调整为使用TypeDescriptionProvider .

第二次编辑:下面是使用TypeDescriptionProvider的完整(但最少的)示例；长代码警告.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
// example
static class Program {
    [STAThread]
    static void Main() { 
        PropertyBag.AddProperty("UserName", typeof(string), new DisplayNameAttribute("User Name"));
        PropertyBag.AddProperty("DateOfBirth", typeof(DateTime), new DisplayNameAttribute("Date of Birth"));
        BindingList<PropertyBag> list = new BindingList<PropertyBag>() {
            new PropertyBag().With("UserName", "Fred").With("DateOfBirth", new DateTime(1998,12,1)),
            new PropertyBag().With("UserName", "William").With("DateOfBirth", new DateTime(1997,4,23))
        };

        Application.Run(new Form {
            Controls = {
                new DataGridView { // prove it works for complex bindings
                    Dock = DockStyle.Fill,
                    DataSource = list,
                    ReadOnly = false, AllowUserToAddRows = true
                }
            },
            DataBindings = {
                {"Text", list, "UserName"} // prove it works for simple bindings
            }
        });
    }
}
// PropertyBag file 1; the core bag
partial class PropertyBag : INotifyPropertyChanged {
    private static PropertyDescriptorCollection props;
    public event PropertyChangedEventHandler PropertyChanged;
    void OnPropertyChanged(string propertyName) {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
    static PropertyBag() {
        props = new PropertyDescriptorCollection(new PropertyDescriptor[0], true);
        // init the provider; I'm avoiding TypeDescriptionProviderAttribute so that we
        // can exploit the default implementation for fun and profit
        TypeDescriptionProvider defaultProvider = TypeDescriptor.GetProvider(typeof(PropertyBag)),
            customProvider = new PropertyBagTypeDescriptionProvider(defaultProvider);
        TypeDescriptor.AddProvider(customProvider, typeof(PropertyBag));
    }
    private static readonly object syncLock = new object();
    public static void AddProperty(string name, Type type, params Attribute[] attributes) {
        lock (syncLock)
        {   // append the new prop, into a *new* collection, so that downstream
            // callers don't have to worry about the complexities
            PropertyDescriptor[] newProps = new PropertyDescriptor[props.Count + 1];
            props.CopyTo(newProps, 0);
            newProps[newProps.Length - 1] = new PropertyBagPropertyDescriptor(name, type, attributes);
            props = new PropertyDescriptorCollection(newProps, true);
        }
    }
    private readonly Dictionary<string, object> values;
    public PropertyBag()
    { // mainly want to enforce that we have a public parameterless ctor
        values = new Dictionary<string, object>();
    }    
    public object this[string key] {
        get {
            if (string.IsNullOrEmpty(key)) throw new ArgumentNullException("key");
            object value;
            values.TryGetValue(key, out value);
            return value;
        }
        set {
            if (string.IsNullOrEmpty(key)) throw new ArgumentNullException("key");
            var prop = props[key];
            if (prop == null) throw new ArgumentException("Invalid property: " + key, "key");
            values[key] = value;
            OnPropertyChanged(key);
        }
    }
    internal void Reset(string key) {
        values.Remove(key);
    }
    internal bool ShouldSerialize(string key) {
        return values.ContainsKey(key);
    }
}

static class PropertyBagExt
{
    // cheeky fluent API to make the example code easier:
    public static PropertyBag With(this PropertyBag obj, string name, object value) {
        obj[name] = value;
        return obj;
    }
}

// PropertyBag file 2: provider / type-descriptor
partial class PropertyBag {
    class PropertyBagTypeDescriptionProvider : TypeDescriptionProvider, ICustomTypeDescriptor {
        readonly ICustomTypeDescriptor defaultDescriptor;
        public PropertyBagTypeDescriptionProvider(TypeDescriptionProvider parent) : base(parent) {
            this.defaultDescriptor = parent.GetTypeDescriptor(typeof(PropertyBag));
        }
        public override ICustomTypeDescriptor GetTypeDescriptor(Type objectType, object instance) {
            return this;
        }
        AttributeCollection ICustomTypeDescriptor.GetAttributes() {
            return defaultDescriptor.GetAttributes();
        }
        string ICustomTypeDescriptor.GetClassName() {
            return defaultDescriptor.GetClassName();
        }
        string ICustomTypeDescriptor.GetComponentName() {
            return defaultDescriptor.GetComponentName();
        }
        TypeConverter ICustomTypeDescriptor.GetConverter() {
            return defaultDescriptor.GetConverter();
        }
        EventDescriptor ICustomTypeDescriptor.GetDefaultEvent() {
            return defaultDescriptor.GetDefaultEvent();
        }
        PropertyDescriptor ICustomTypeDescriptor.GetDefaultProperty() {
            return defaultDescriptor.GetDefaultProperty();
        }
        object ICustomTypeDescriptor.GetEditor(Type editorBaseType) {
            return defaultDescriptor.GetEditor(editorBaseType);
        }
        EventDescriptorCollection ICustomTypeDescriptor.GetEvents(Attribute[] attributes) {
            return defaultDescriptor.GetEvents(attributes);
        }
        EventDescriptorCollection ICustomTypeDescriptor.GetEvents() {
            return defaultDescriptor.GetEvents();
        }
        PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties(Attribute[] attributes) {
            return PropertyBag.props; // should really be filtered, but meh!
        }
        PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties() {
            return PropertyBag.props;
        }
        object ICustomTypeDescriptor.GetPropertyOwner(PropertyDescriptor pd) {
            return defaultDescriptor.GetPropertyOwner(pd);
        }
    }
}
// PropertyBag file 3: property descriptor
partial class PropertyBag {
    class PropertyBagPropertyDescriptor : PropertyDescriptor {
        private readonly Type type;
        public PropertyBagPropertyDescriptor(string name, Type type, Attribute[] attributes)
            : base(name, attributes) {
            this.type = type;
        }
        public override object GetValue(object component) {
            return ((PropertyBag)component)[Name];
        }
        public override void SetValue(object component, object value) {
            ((PropertyBag)component)[Name] = value;
        }
        public override void ResetValue(object component) {
            ((PropertyBag)component).Reset(Name);
        }
        public override bool CanResetValue(object component) {
            return true;
        }
        public override bool ShouldSerializeValue(object component) {
            return ((PropertyBag)component).ShouldSerialize(Name);
        }
        public override Type PropertyType {
            get { return type; }
        }
        public override bool IsReadOnly {
            get { return false; }
        }
        public override Type ComponentType {
            get { return typeof(PropertyBag); }
        }
    }
}