关于反射中Assembly.Load("程序集").CreateInstance("命名空间.类")与Activator.CreateInstance()方法

 

动态创建类对象，大多是Activator.CreateInstance()和Activator.CreateInstance<T>()方法，有的用了Assembly.Load("AssemblyName").CreateInstance ("ClassName");的方法，研究一下这两者到底有什么区别

System.Reflection.Assembly位于mscorlib.dll里，CreateInstance()方法的源码是这样的

 

 

public object CreateInstance(string typeName, bool ignoreCase, BindingFlags bindingAttr, Binder binder, object[] args, CultureInfo culture, object[]

activationAttributes)
{
      Type type1 = this.GetTypeInternal(typeName, false, ignoreCase, false);
      if (type1 == null)
      {
            return null;
      }
      //注意一下这一句，晕。。。。这里居然调用了Activator.CreateInstance方法
      return Activator.CreateInstance(type1, bindingAttr, binder, args, culture, activationAttributes);
}

System.Activator也位于mscorlib.dll里，CreateInstance()方法的
源码如下

public static object CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, object[] args, CultureInfo culture, object[] activationAttributes)
{
      object obj1;
      if (type == null)
      {
            throw new ArgumentNullException("type");
      }
      if (type is TypeBuilder)
      {
            throw new NotSupportedException(Environment.GetResourceString("NotSupported_CreateInstanceWithTypeBuilder"));
      }
      if ((bindingAttr & ((BindingFlags) 0xff)) == BindingFlags.Default)
      {
            bindingAttr |= BindingFlags.CreateInstance | BindingFlags.Public | BindingFlags.Instance;
      }
      if ((activationAttributes != null) && (activationAttributes.Length > 0))
      {
            if (!type.IsMarshalByRef)
            {
                  throw new NotSupportedException(Environment.GetResourceString("NotSupported_ActivAttrOnNonMBR"));
            }
            if (!type.IsContextful && ((activationAttributes.Length > 1) || !(activationAttributes[0] is UrlAttribute)))
            {
                  throw new NotSupportedException(Environment.GetResourceString("NotSupported_NonUrlAttrOnMBR"));
            }
      }
      try
      {
            obj1 = ((RuntimeType) type.UnderlyingSystemType).CreateInstanceImpl(bindingAttr, binder, args, culture, activationAttributes);
      }
      catch (InvalidCastException)
      {
            throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "type");
      }
      return obj1;
}
===================================================================================

DALFactory默认是每一层封装到一个程序集（独立项目）组件里。通过反射机制创建对象实例。

//从程序集创建对象实例
string path = System.Configuration.ConfigurationSettings.AppSettings["DAL"];//数据层的程序集名称
return (IDbObject)Assembly.Load(path).CreateInstance(path+".DbObject");

如果你的数据层不是单独的程序集,可以采用如下方法加载：
//使用与指定参数匹配程度最高的构造函数来创建指定类型的实例
string path = System.Configuration.ConfigurationSettings.AppSettings["DAL"];
string TypeName=path+".DbObject"
Type objType = Type.GetType(TypeName,true);
return (IDbObject)Activator.CreateInstance(objType);