Question

如何获取类或属性的自定义特性

Answer 1

1. 定义一个以Attribute结尾的特性类, 特性类继承自System.Attribute, 如下所示.
[AttributeUsage(AttributeTargets.Property, AllowMultiple=false)]
public class PrimaryKeyAttribute : System.Attribute
{
.............

其中AttributeTargets是一个枚举的值, 可以是: Assembly | Module | Class | Struct | Enum | Constructor | Method | Property | Field | Event | Interface | Parameter | Delegate

2. 在需要使用的地方使用PrimaryKey自定义特性标签, 如下所示.
[PrimaryKey(Column = "CustomerID", IsIdentity=false)]
public int ID
{
.............

3. 为了获取自定义特性的信息, 需要反射的方式获取其数据, 首先我们定义一个类来存储这些信息, 如下所示
public class PrimaryKeyModel
{
private readonly PropertyInfo propertyInfo;//外键的属性字段信息
private readonly PrimaryKeyAttribute primaryKeyAtt;//外键的特性信息
................

public static PrimaryKeyModel GetPrimaryKey(Type type)
{
PropertyInfo[] properties = type.GetProperties();
foreach (PropertyInfo p in properties)
{
object[] keys = p.GetCustomAttributes(typeof(PrimaryKeyAttribute), true);
if (keys.Length == 1)
{
return new PrimaryKeyModel(p, keys[0] as PrimaryKeyAttribute);
}
}
return null;
}

4. 在Customer类中获取其特性的信息代码如下
string strReturn = string.Empty;
//Get PrimaryKey Name
PrimaryKeyModel attribute= PrimaryKeyModel.GetPrimaryKey(this.GetType());
if(attribute != null)
{
strReturn += string.Format("PrimaryKey Name:{0} IsIdentity:{1} Column:{2}\r\n",
attribute.Property.Name, attribute.PrimaryKeyAtt.IsIdentity, attribute.PrimaryKeyAtt.Column);
}

Answer 2

1. 定义一个以Attribute结尾的特性类, 特性类继承自System.Attribute, 如下所示.
[AttributeUsage(AttributeTargets.Property, AllowMultiple=false)]
public class PrimaryKeyAttribute : System.Attribute
{
.............

其中AttributeTargets是一个枚举的值, 可以是: Assembly | Module | Class | Struct | Enum | Constructor | Method | Property | Field | Event | Interface | Parameter | Delegate

2. 在需要使用的地方使用PrimaryKey自定义特性标签, 如下所示.
[PrimaryKey(Column = "CustomerID", IsIdentity=false)]
public int ID
{
.............

3. 为了获取自定义特性的信息, 需要反射的方式获取其数据, 首先我们定义一个类来存储这些信息, 如下所示
public class PrimaryKeyModel
{
private readonly PropertyInfo propertyInfo;//外键的属性字段信息
private readonly PrimaryKeyAttribute primaryKeyAtt;//外键的特性信息
................

public static PrimaryKeyModel GetPrimaryKey(Type type)
{
PropertyInfo[] properties = type.GetProperties();
foreach (PropertyInfo p in properties)
{
object[] keys = p.GetCustomAttributes(typeof(PrimaryKeyAttribute), true);
if (keys.Length == 1)
{
return new PrimaryKeyModel(p, keys[0] as PrimaryKeyAttribute);
}
}
return null;
}

4. 在Customer类中获取其特性的信息代码如下
string strReturn = string.Empty;
//Get PrimaryKey Name
PrimaryKeyModel attribute= PrimaryKeyModel.GetPrimaryKey(this.GetType());
if(attribute != null)
{
strReturn += string.Format("PrimaryKey Name:{0} IsIdentity:{1} Column:{2}\r\n",
attribute.Property.Name, attribute.PrimaryKeyAtt.IsIdentity, attribute.PrimaryKeyAtt.Column);
}