在编程接口时，我发现我做了很多强制转换或对象类型转换。
这两种转换方法有什么区别吗?如果是的话，是否有成本差异，或者这对我的程序有什么影响?
public interface IMyInterface
{
void AMethod();
}
public class MyClass : IMyInterface
{
public void AMethod()
{
//Do work
}
// Other helper methods....
}
public class Implementation
{
IMyInterface _MyObj;
MyClass _myCls1;
MyClass _myCls2;
public Implementation()
{
_MyObj = new MyClass();
// What is the difference here:
_myCls1 = (MyClass)_MyObj;
_myCls2 = (_MyObj as MyClass);
}
}
另外，“一般来说”首选的方法是什么?
除了这里已经暴露的所有内容，我刚刚发现了一个我认为值得注意的实际差异，在显式选角之间
var x = (T) ...
相对于使用as操作符。
下面是例子:
class Program
{
static void Main(string[] args)
{
Console.WriteLine(GenericCaster<string>(12345));
Console.WriteLine(GenericCaster<object>(new { a = 100, b = "string" }) ?? "null");
Console.WriteLine(GenericCaster<double>(20.4));
//prints:
//12345
//null
//20.4
Console.WriteLine(GenericCaster2<string>(12345));
Console.WriteLine(GenericCaster2<object>(new { a = 100, b = "string" }) ?? "null");
//will not compile -> 20.4 does not comply due to the type constraint "T : class"
//Console.WriteLine(GenericCaster2<double>(20.4));
}
static T GenericCaster<T>(object value, T defaultValue = default(T))
{
T castedValue;
try
{
castedValue = (T) Convert.ChangeType(value, typeof(T));
}
catch (Exception)
{
castedValue = defaultValue;
}
return castedValue;
}
static T GenericCaster2<T>(object value, T defaultValue = default(T)) where T : class
{
T castedValue;
try
{
castedValue = Convert.ChangeType(value, typeof(T)) as T;
}
catch (Exception)
{
castedValue = defaultValue;
}
return castedValue;
}
}
底线:GenericCaster2不能用于结构类型。GenericCaster意志。
如果您使用针对。net Framework 4的Office PIAs。X你应该使用as关键字，否则它将无法编译。
Microsoft.Office.Interop.Outlook.Application o = new Microsoft.Office.Interop.Outlook.Application();
Microsoft.Office.Interop.Outlook.MailItem m = o.CreateItem(Microsoft.Office.Interop.Outlook.OlItemType.olMailItem) as Microsoft.Office.Interop.Outlook.MailItem;
当目标是。net 2.0时，强制转换是可以的:
Microsoft.Office.Interop.Outlook.MailItem m = (Microsoft.Office.Interop.Outlook.MailItem)o.CreateItem(Microsoft.Office.Interop.Outlook.OlItemType.olMailItem);
当目标是。net 4时。X的误差为:
缺少编译器需要的成员'Microsoft.CSharp.RuntimeBinder.Binder.Convert'
缺少编译器需要的成员'Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo.Create'
