.NET 4.0 beta 2有 introduced IObservable和 IObserver接口(interface)。
与经典 .NET 事件相比有哪些优势?这不是解决同样的问题吗?
最佳答案
您可以将 IObservable 用作事件,将暴露事件的代码替换为 IObservable 类型的属性,但这并不是重点。
关于 IObservable,有两件重要的事情需要理解:
这是我今天下午在工作中遇到的一个例子。
在 Silverlight 中,您可以将某些效果应用于无法应用于普通控件的图像控件。为了在控件的内容发生更改时绕过这些限制,我可以等待其视觉外观更新并对其进行截图。然后我想隐藏它的视觉表示,用快照替换它,并将视觉效果应用到图像上。现在我可以将图像效果应用于控件(假设它不是交互式的)。
这个程序将是微不足道的,但它必须是异步的。在我可以对图像应用效果之前,我必须等待两个连续的异步操作完成:
以下是我使用 Rx 解决此问题的方法:
// A content control is a control that displays content. That content can be
// anything at all like a string or another control. Every content control contains
// another control: a ContentPresenter. The ContentPresenter's job is to generate
// a visual representation of the Content property. For example, if the Content property
// of the ContentControl is a string, the ContentPresenter creates a TextBlock and inserts
// the string into it. On the other hand if the Content property is another control the
// ContentPresenter just inserts it into the visual tree directly.
public class MyContentControl : ContentControl
{
// A subject implements both IObservable and IObserver. When IObserver methods
// are called, it forwards those calls to all of its listeners.
// As a result it has roughly the same semantics as an event that we can "raise."
private Subject<object> contentChanged = new Subject<object>();
// This is a reference to the ContentPresenter in the ContentControl's template
private ContentPresenter contentPresenter;
// This is a reference to the Image control within ContentControl's template. It is displayed on top of the ContentPresenter and has a cool blur effect applied to it.
private Image contentImageControl;
public MyContentControl()
{
// Using Rx we can create specific events from general events.
// In this case I want to create a specific event ("contentImageChanged") which
// gives me exactly the data I need to respond and update the UI.
var contentImageChanged =
// get the content from the content changed event
from content in contentChanged
where content != null
// Wait for the ContentPresenter's visual representation to update.
// ContentPresenter is data bound to the Content property, so it will
// update momentarily.
from _ in contentPresenter.GetLayoutUpdated().Take(1)
select new WritableBitmap(contentPresenter, new TranslateTransform());
contentImageChanged.Subscribe(
contentImage =>
{
// Hide the content presenter now that we've taken a screen shot
contentPresenter.Visibility = Visibility.Collapsed;
// Set the image source of the image control to the snapshot
contentImageControl.ImageSource = contentImage;
});
}
// This method is invoked when the Content property is changed.
protected override OnContentChanged(object oldContent, object newContent)
{
// show the content presenter before taking screenshot
contentPresenter.Visibility = Visibility.Visible;
// raise the content changed "event"
contentChanged.OnNext(newContent);
base.OnContentChanged(oldContent, newContent);
}
}
这个例子特别简单,因为只有两个连续的操作要排序。即使在这个简单的示例中,我们也可以看到 Rx 增加了值(value)。如果没有它,我将不得不使用状态变量来确保事件按特定顺序触发。我还必须编写一些非常丑陋的代码来明确地从 LayoutUpdated 事件中分离出来。
当你使用 Rx 编程时,诀窍是思考“我希望我的框架提供什么事件?”然后去创建它。我们被训练将事件视为简单的、输入驱动的事物(“mouseover”、“mouseclick”、“keyup”等)。但是,事件没有理由不能非常复杂且特定于您的应用程序(“GoogleMsdnMashupStockDataArrived”、“DragStarting”和“ImageContentChanged”)。当您以这种方式构建程序时(准确地创建我需要的事件 ,然后 通过更改状态来响应它),您会发现它们的状态错误更少,变得更有条理,并且更加自我描述。
知道了? :-)
关于.net - .NET Rx 相对于经典事件的优势?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1212536/