DataGridView不显示实现ICustomTypeDescriptor的对象的属性 [英] DataGridView not showing properites of objects which implement ICustomTypeDescriptor
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问题描述
我在 DataGridView 中显示对象列表。一切都很好。根据对象的属性将列自动添加到 DataGridView 中。
现在，我将网格中显示的类更改为实现 ICustomTypeDescriptor 。但是现在，当我将 DataSource 设置为我的自定义对象列表时，现在网格不再显示任何列或行。
我是猜测这与使用 ICustomTypeDescriptor 的事实有关，每个网格的每行显示的每个实例可能会返回一组不同的属性。
我正在实现 ICustomTypeDescriptor ，以便我可以允许用户在运行时向对象动态添加自定义属性。这些自定义属性应该通过 DataGridView 可见和可编辑。
为什么 DataGridView 看不到我的 ICustomTypeDescriptor 方法？有另外一种方法，我可以动态地添加属性到一个将显示在 DataGridView 中的对象。
解决方案
DataGridView 查看元数据的列表版本;这个规则是...复杂：
- 如果数据源实现
IListSource，GetList（）被评估并用作数据源（继续为2） - 如果数据源实现
ITypedList，GetProperties（）用于获取元数据（退出） - 如果可以找到一个类型（非
对象）索引器（即public T this [int index]），那么T通过TypeDescriptor.GetProperties（type）用作源代码：
- 如果分配了
TypeDescriptionProvider，则根据类型（退出）使用此元数据 - 否则反射用于元数据（退出）
- 如果分配了
- 如果列表不为空，则第一个对象通过
TypeDescriptor.GetProperties（list [0]）：
- if
ICustomTypeDescriptor被实现，然后它被使用（exit）[*] - 如果分配了一个
TypeDescriptionProvider，则根据类型（exit）[*] - 否则使用反射（退出）
- if
- else元数据不可用（退出）
（[*] =我不记得这两个方法去哪里了...）
如果您使用列表< T> （或类似），则您打到最简单（IMO）案例 - ＃3。如果要提供自定义元数据，那么;最好是写一个 TypeDescriptionProvider 并将其与该类型相关联。我可以写一个例子，但需要一段时间（在火车上，大概）...
- if a
TypeDescriptionProvideris assigned, the this is used for metadata against the type (exit) - otherwise reflection is used for metadata (exit)
TypeDescriptor.GetProperties(list[0]):
- if
ICustomTypeDescriptoris implemented, then it is used (exit) [*] - if a
TypeDescriptionProvideris assigned, the this is used for metadata against the type (exit) [*] - otherwise reflection is used (exit)
([*]=I can't remember which way around these two go...)
If you are using List<T> (or similar), then you hit the "simplest" (IMO) case - #3. If you want to provide custom metadata, then; you best bet is to write a TypeDescriptionProvider and associate it with the type. I can write an example but it'll take a while (on the train, probably)...
Edit: here's an example that uses ITypedList; I'll try to tweak it to use TypeDescriptionProvider instead...
Second edit: a full (yet minimal) example using TypeDescriptionProvider follows; long code warning...
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); }
}
}
}
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