Observable.FromEvent TDelegate， TEventArgs < 方法 (Func < Action < TEventArgs >> ， TDelegate > ， Action TDelegate， Action << TDelegate >>)
將 .NET 事件轉換為可觀察的序列。
Namespace：System.Reactive.Linq
裝配： System.Reactive.dll) 中的 System.Reactive (
Syntax
'Declaration
Public Shared Function FromEvent(Of TDelegate, TEventArgs) ( _
conversion As Func(Of Action(Of TEventArgs), TDelegate), _
addHandler As Action(Of TDelegate), _
removeHandler As Action(Of TDelegate) _
) As IObservable(Of TEventArgs)
'Usage
Dim conversion As Func(Of Action(Of TEventArgs), TDelegate)
Dim addHandler As Action(Of TDelegate)
Dim removeHandler As Action(Of TDelegate)
Dim returnValue As IObservable(Of TEventArgs)
returnValue = Observable.FromEvent(conversion, _
addHandler, removeHandler)
public static IObservable<TEventArgs> FromEvent<TDelegate, TEventArgs>(
Func<Action<TEventArgs>, TDelegate> conversion,
Action<TDelegate> addHandler,
Action<TDelegate> removeHandler
)
public:
generic<typename TDelegate, typename TEventArgs>
static IObservable<TEventArgs>^ FromEvent(
Func<Action<TEventArgs>^, TDelegate>^ conversion,
Action<TDelegate>^ addHandler,
Action<TDelegate>^ removeHandler
)
static member FromEvent :
conversion:Func<Action<'TEventArgs>, 'TDelegate> *
addHandler:Action<'TDelegate> *
removeHandler:Action<'TDelegate> -> IObservable<'TEventArgs>
JScript does not support generic types and methods.
類型參數
- TDelegate
委派的類型。
- TEventArgs
事件的類型。
參數
- 轉換
類型：System.Func<Action< TEventArgs > 、TDelegate>
函式，用來將指定的事件處理常式轉換為與基礎 .NET 事件相容的委派。 產生的委派用於對 addHandler 和 removeHandler 動作參數的呼叫。
- addHandler
類型：System.Action< TDelegate>
將指定事件處理常式附加至基礎 .NET 事件的動作。
- removeHandler
類型：System.Action< TDelegate>
從基礎 .NET 事件中斷連結指定事件處理常式的動作。
傳回值
類型：System.IObservable< TEventArgs>
可觀察序列，其中包含基礎 .NET 事件調用的資料表示。
備註
FromEvent 運算子會在引發事件時，建立與基礎事件一起提供之事件引數的可觀察序列。 FromEvent 運算子只適用于 Action < T > 類型的委派。 因此，轉換函式必須用來建立與基礎 .NET 事件相容的事件處理常式。 本主題中的範例程式碼示範 System.IO.FileSystemEventHandler 和 System.IO.RenamedEventHandler 委派的這個轉換。
範例
此範例程式碼示範如何使用 FromEvent 運算子接聽 System.IO.FileSystemWatcher 上的建立、重新命名和刪除事件。 此範例會在 C：\Users\Public 資料夾中監看這些事件。 FromEvent 運算子只支援 Action < T > 類型的委派。 因此，此範例會使用轉換參數來定義 Lambda 運算式，將 System T > 委派轉換成 System.IO.FileSystemEventHandler < 和 System.IO.RenamedEventHandler 委派。 事件是使用每個可觀察序列的訂用帳戶來觀察。 每個事件都會寫入主控台視窗。
using System;
using System.Reactive.Linq;
using System.IO;
namespace Example
{
class Program
{
static void Main()
{
//*********************************************************************************************************************//
//*** Create a FileSystemWatcher to watch the C:\Users\Public directory using the default NotifyFilter watching for ***//
//*** changes to any type of file. ***//
//*********************************************************************************************************************//
FileSystemWatcher fsw = new FileSystemWatcher(@"C:\Users\Public", "*.*");
fsw.EnableRaisingEvents = true;
//******************************************************************************************//
//*** Use the FromEvent operator to setup a subscription to the Created event. ***//
//*** ***//
//*** The first lambda expression performs the conversion of Action<FileSystemEventArgs> ***//
//*** to FileSystemEventHandler. The FileSystemEventHandler just calls the handler ***//
//*** passing the FileSystemEventArgs. ***//
//*** ***//
//*** The other lambda expressions add and remove the FileSystemEventHandler to and from ***//
//*** the event. ***//
//******************************************************************************************//
var fswCreated = Observable.FromEvent<FileSystemEventHandler, FileSystemEventArgs>(handler =>
{
FileSystemEventHandler fsHandler = (sender, e) =>
{
handler(e);
};
return fsHandler;
},
fsHandler => fsw.Created += fsHandler,
fsHandler => fsw.Created -= fsHandler);
fswCreated.Subscribe(e => Console.WriteLine("{0} was created.", e.FullPath));
//******************************************************************************************//
//*** Use the FromEvent operator to setup a subscription to the Renamed event. ***//
//*** ***//
//*** The first lambda expression performs the conversion of Action<RenamedEventArgs> ***//
//*** to RenamedEventHandler. The RenamedEventHandler just calls the handler passing the ***//
//*** RenamedEventArgs. ***//
//*** ***//
//*** The other lambda expressions add and remove the RenamedEventHandler to and from ***//
//*** the event. ***//
//******************************************************************************************//
var fswRenamed = Observable.FromEvent<RenamedEventHandler, RenamedEventArgs>(handler =>
{
RenamedEventHandler fsHandler = (sender, e) =>
{
handler(e);
};
return fsHandler;
},
fsHandler => fsw.Renamed += fsHandler,
fsHandler => fsw.Renamed -= fsHandler);
fswRenamed.Subscribe(e => Console.WriteLine("{0} was renamed to {1}.", e.OldFullPath, e.FullPath));
//******************************************************************************************//
//*** Use the FromEvent operator to setup a subscription to the Deleted event. ***//
//*** ***//
//*** The first lambda expression performs the conversion of Action<FileSystemEventArgs> ***//
//*** to FileSystemEventHandler. The FileSystemEventHandler just calls the handler ***//
//*** passing the FileSystemEventArgs. ***//
//*** ***//
//*** The other lambda expressions add and remove the FileSystemEventHandler to and from ***//
//*** the event. ***//
//******************************************************************************************//
var fswDeleted = Observable.FromEvent<FileSystemEventHandler, FileSystemEventArgs>(handler =>
{
FileSystemEventHandler fsHandler = (sender, e) =>
{
handler(e);
};
return fsHandler;
},
fsHandler => fsw.Deleted += fsHandler,
fsHandler => fsw.Deleted -= fsHandler);
fswDeleted.Subscribe(e => Console.WriteLine("{0} was deleted.", e.FullPath));
Console.WriteLine("Press ENTER to exit...\n");
Console.ReadLine();
}
}
}
下列輸出是使用範例程式碼所產生。
Press ENTER to exit...
C:\Users\Public\New Text Document.txt was created.
C:\Users\Public\New Text Document.txt was renamed to C:\Users\Public\TestFile.txt.
C:\Users\Public\TestFile.txt was deleted.