Event.filter<'T,'Del> Function (F#)

Returns a new event that listens to the original event and triggers the resulting event only when the argument to the event passes the given function.

Namespace/Module Path: Microsoft.FSharp.Control.Event

Assembly: FSharp.Core (in FSharp.Core.dll)

// Signature:
Event.filter : ('T -> bool) -> IEvent<'Del,'T> -> IEvent<'T> (requires delegate)

// Usage:
Event.filter predicate sourceEvent

Parameters

• predicate
  Type: 'T -> bool

  The function to determine which triggers from the event to propagate.

• sourceEvent
  Type: IEvent<'Del,'T>

  The input event.

Return Value

An event that only passes values that pass the predicate.

Remarks

This function is named Filter in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

Example

The following code example shows how to use the Event.filter function. In this example, mouse events are passed on only when the mouse pointer is in a certain region.

let form = new Form(Text = "F# Windows Form",
                    Visible = true,
                    TopMost = true)
form.MouseMove
    |> Event.filter ( fun evArgs -> evArgs.X > 100 && evArgs.Y > 100)
    |> Event.add ( fun evArgs ->
        form.BackColor <- System.Drawing.Color.FromArgb(
            evArgs.X, evArgs.Y, evArgs.X ^^^ evArgs.Y) )

Platforms

Windows 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2

Version Information

F# Runtime

Supported in: 2.0, 4.0

Silverlight

Supported in: 3

See Also

Reference

Control.Event Module (F#)

Microsoft.FSharp.Control Namespace (F#)

Change History

Date	History	Reason
September 2010	Added code example.	Information enhancement.