避免10 个常见ASP.NET缺陷 使网站平稳运行
View State: The Silent Perf Killer
视图状态：无声的性能杀手
In some ways, view state is the greatest thing since sliced bread. After all, it’s view state that allows pages and controls to persist state across postbacks. That’s why you don’t have to write code to keep the text in a TextBox from disappearing when a button is clicked as you did in classic ASP, or requery a database and rebind a DataGrid following a postback.
从某种意义上说，视图状态是有史以来最伟大的事情。毕竟，视图状态使得页面和控件能够在回发之间保持状态。因此，您不必像在传统的 ASP 中那样编写代码，以防止在单击按钮时文本框中的文本消失，或在回发后重新查询数据库和重新绑定 DataGrid。
But view state has a dark side, too: when it grows too large, it’s a silent performance killer. Some controls, such as TextBoxes, are judicious with view state. Others, notably DataGrids and GridViews, emit view state in proportion to the amount of information displayed. I cringe when I see a GridView displaying 200 or 300 rows of data. Even though ASP.NET 2.0 view state is roughly half the size of ASP.NET 1.x view state, one lousy GridView can easily cut the effective bandwidth of a connection between a browser and a Web server by 50 percent or more.
但是视图状态也有缺点：当它增长得过大时，它便成为一个无声的性能杀手。某些控件（例如文本框）会根据视图状态作出相应判断。其他控件（特别是 DataGrid 和 GridView）则根据显示的信息量确定视图状态。如果 GridView 显示 200 或 300 行数据，我会望而生畏。即使 ASP.NET 2.0 视图状态大致是 ASP.NET 1 x 视图状态的一半大小，一个糟糕的 GridView 也可以容易地将浏览器和 Web 服务器之间的连接的有效带宽减少 50％ 或更多。
You can turn off view state for individual controls by setting EnableViewState to false, but some controls, particularly DataGrids, lose some of their functionality when denied the freedom to use view state. A much better solution to taming view state is keeping it on the server. In ASP.NET 1.x, you can override a page’s LoadPageStateFromPersistenceMedium and SavePageStateToPersistenceMedium methods and handle view state however you like. The overrides shown in the code in Figure 4 prevent view state from being persisted in a hidden field and persist it in session state instead. Storing view state in session state is particularly effective when paired with the default session state process model—that is, when session state is stored in memory in the ASP.NET worker process. If session state is stored in a database instead, then only testing will show whether keeping view state in session state improves or degrades performance.
您可以通过将 EnableViewState 设置为 false 来关闭单个控件的视图状态，但某些控件（特别是 DataGrid）在不能使用视图状态时会失去某些功能。控制视图状态的更佳解决方案是将其保留在服务器上。在 ASP.NET 1.x 中，您可以重写页面的 LoadPageStateFromPersistenceMedium 和 SavePageStateToPersistenceMedium 方法并按您喜欢的方式处理视图状态。图4 中的代码显示的重写可防止视图状态保留在隐藏字段中，而将其保留在会话状态中。当与默认会话状态进程模型一起使用时（即，会话状态存储在内存中的 ASP.NET 辅助进程中时），在会话状态中存储视图状态尤其有效。相反，如果会话状态存储在数据库中，则只有测试才能显示在会话状态中保留视图状态会提高还是降低性能。
The same technique works in ASP.NET 2.0, but ASP.NET 2.0 offers a simpler means for persisting view state in session state. You begin by defining a custom page adapter whose GetStatePersister method returns an instance of the .NET Framework SessionPageStatePersister class:
在 ASP.NET 2.0 中使用相同的方法，但是 ASP.NET 2.0 能够提供更简单的方法将视图状态保留在会话状态中。
首先，定义一个自定义页适配器，其 GetStatePersister 方法返回 .NET Framework SessionPageStatePersister 类的一个实例：
public class SessionPageStateAdapter :System.Web.UI.Adapters.PageAdapter{public override PageStatePersister GetStatePersister (){return new SessionPageStatePersister(this.Page);}}
Then you register the custom page adapter as the default page adapter by dropping an App.browsers file like the following into the application’s App_Browsers folder:
然后，通过将 App.browsers 文件按以下方式放入应用程序的 App_Browsers 文件夹，将自定义页适配器注册为默认页适配器：
<browsers><browser refID="Default"><controlAdapters><adapter controlType="System.Web.UI.Page"adapterType="SessionPageStateAdapter" /></controlAdapters></browser></browsers>
(You can name the file anything you like as long as it has a .browsers extension.) Thereafter, ASP.NET will load the page adapter and use the returned SessionPageStatePersister to persist all page state, including view state.
One downside to using a custom page adapter is that it acts globally for every page in the application. If you’d prefer to persist view state in session state for some pages but not for others, use the technique shown in Figure 4. Additionally, you can run into issues with this technique if a user creates multiple browser windows within the same session.
（您可以将文件命名为您喜欢的任何名称，只要它的扩展名为 .browsers 即可。）此后，ASP.NET 将加载页适配器并使用返回的 SessionPageStatePersister 以保留所有页面状态，包括视图状态。
使用自定义页适配器的一个缺点是它全局性地作用于应用程序中的每一页。如果您更愿意将其中一些页面的视图状态保留在会话状态中而不保留其他页面的视图状态，请使用 图4 中显示的方法。另外，如果用户在同一会话中创建多个浏览器窗口，您使用该方法可能会遇到问题。
from:asp学习网/title:避免10 个常见ASP.NET缺陷 使网站平稳运行/ time:2007-5-20 17:41:09
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