强制演员 [英] Force a cast
问题描述
我想从类外部访问页面对象的视图状态
（在帮助器类中），所以我创建了一个继承自Page的类，并公开了一个
返回viewstate对象的属性。我的帮助类我将
页面转换为我的页面类并访问公开的属性，但是强制转换导致
指定的强制转换无效异常。我曾经在delphi和
c ++中一直访问受保护的东西，是否可以在.NET中使用？
" Jeremy Chapman" < me@here.com>在消息中写道
新闻：％2 **************** @ TK2MSFTNGP14.phx.gbl ...我想要从类的外部访问页面对象的视图状态（在辅助类中），所以我创建了一个继承自Page的类，并公开了一个返回viewstate对象的
属性。我的帮助类我将
页面转换为我的页面类并访问公开的属性，但是强制转换导致指定的强制转换无效异常。我曾经在delphi
和c ++中一直这样做以访问受保护的东西，是否可以在.NET中？
在.NET中可以进行强制转换。发布实际的源代码，它会更容易
来帮助你。
- Oliver
< blockquote>我认为你认为你曾经在Delphi中这么做过，但它根本不是
。为什么？因为你只能将一个类型转换为它所属的类型，它是一个类型，它是它的类型，还是它继承的类型。由于您的自定义类
继承了System.Web.UI.Page，您可以将IT转换为System.Web.UI.Page类，
但是您无法投射System.Web.UI.Page类作为您的自定义类。
然而，请加油助威。事实上，你的解决方案是不必要的复杂。
请记住，你的页面不是System.Web.UI.Page类，而是
" YourClassName" class，继承System.Web.UI.Page。 IT可以使用自己的ViewState访问
，并可以通过您选择的任何方法公开它。
-
HTH，
Kevin Spencer
Microsoft MVP
..Net开发人员
期待未被接受。
" Jeremy Chapman" < me@here.com>在消息中写道
新闻：％2 **************** @ TK2MSFTNGP14.phx.gbl ...
我想要从类的外部访问页面对象的视图状态（在辅助类中），所以我创建了一个继承自Page的类，并公开了一个返回viewstate对象的
属性。我的帮助类我将
页面转换为我的页面类并访问公开的属性，但是强制转换导致指定的强制转换无效异常。我曾经在delphi
和c ++中一直这样做以访问受保护的东西，是否可以在.NET？
这里有一些样本来源。
使用系统;
名称空间Mynamespace
{
/ //< summary>
///页面的帮助函数
///< / summary>
公共类HelperClass
{
public HelperClass
{
//
// TODO：Add构造函数逻辑这里
//
}
私有类CustomPage：System.Web.UI.Page
{
public CustomPage（）
{
}
public System.Web.UI.StateBag PublishViewState
{
get
{
返回ViewState;
}
}
}
public static void HelperTest（System.Web.UI.Page pPage）
{
CustomPage pPageCustom =（CustomPage）pPage;
pPageCustom.PublishViewState [" test"] = DateTime.Now;
}
}
}
" Oliver Wong" <流*** @ castortech.com>在消息中写道
新闻：Q18Le.195006
I want to access the viewstate of a page object from outside of the class
(in a helper class), so I made a class inherited from Page, and exposed a
property that returns the viewstate object. I my helper class I cast the
page to my page class and access the exposed property, but the cast causes
an ''Specified cast is not valid'' exception. I used to do this in delphi and
c++ all the time to access protected stuff, is it possible in .NET?
"Jeremy Chapman" <me@here.com> wrote in message
news:%2****************@TK2MSFTNGP14.phx.gbl...I want to access the viewstate of a page object from outside of the class
(in a helper class), so I made a class inherited from Page, and exposed a
property that returns the viewstate object. I my helper class I cast the
page to my page class and access the exposed property, but the cast causes
an ''Specified cast is not valid'' exception. I used to do this in delphi
and c++ all the time to access protected stuff, is it possible in .NET?
Casting is possible in .NET. Post actual source code and it''ll be easier
to help you.
- Oliver
I think you THINK you used to so this in Delphi, but it is simply not
possible. Why? Because you can only cast a type as a type that it IS, that
is, the type that it is, or a type that it inherits. Since your custom class
inherits System.Web.UI.Page, you can cast IT as a System.Web.UI.Page class,
but you can not cast a System.Web.UI.Page class as your custom class.
However, be of good cheer. In fact, your solution is needlessly complex.
Remember that your Page is not a System.Web.UI.Page class, but a
"YourClassName" class, which inherits System.Web.UI.Page. IT has access to
its own ViewState, and can expose it via any method you choose.
--
HTH,
Kevin Spencer
Microsoft MVP
..Net Developer
Expect the unaccepted.
"Jeremy Chapman" <me@here.com> wrote in message
news:%2****************@TK2MSFTNGP14.phx.gbl...I want to access the viewstate of a page object from outside of the class
(in a helper class), so I made a class inherited from Page, and exposed a
property that returns the viewstate object. I my helper class I cast the
page to my page class and access the exposed property, but the cast causes
an ''Specified cast is not valid'' exception. I used to do this in delphi
and c++ all the time to access protected stuff, is it possible in .NET?
Here is some sample source.
using System;
namespace Mynamespace
{
/// <summary>
/// Helper functions for a page
/// </summary>
public class HelperClass
{
public HelperClass
{
//
// TODO: Add constructor logic here
//
}
private class CustomPage : System.Web.UI.Page
{
public CustomPage()
{
}
public System.Web.UI.StateBag PublishViewState
{
get
{
return ViewState;
}
}
}
public static void HelperTest(System.Web.UI.Page pPage)
{
CustomPage pPageCustom = (CustomPage)pPage;
pPageCustom.PublishViewState["test"] = DateTime.Now;
}
}
}
"Oliver Wong" <ow***@castortech.com> wrote in message
news:Q18Le.195006
这篇关于强制演员的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
