Xamarin.Forms Guides | Samples

Xamarin.Forms.EventTrigger Class

Class that represents a triggering event and a list of TriggerAction objects that will be invoked when the event is raised.

Syntax

[Xamarin.Forms.ContentProperty("Actions")]
public sealed class EventTrigger : TriggerBase

Remarks

The example below shows how developers can use an event trigger to respond to events and update the value of a control property.

With the ColorTriggerAction class below defined in the TriggerDemo namespace:

C# Example

public class ColorTriggerAction : TriggerAction<Entry>
{
  protected override void Invoke(Entry sender)
  {
      Color[] color ={ Color.Red,
                       Color.Orange,
                       Color.Yellow,
                       Color.Green,
                       Color.Blue,
                       Color.Indigo,
                       Color.Violet };
      sender.TextColor = color[sender.Text.Length % color.Length];
  }
}

the developer can use the XAML below to create a page that cycles the colors of a Entry text area through the colors of the rainbow as the user enters text.

XAML Example

<?xml version="1.0" encoding="utf-8"?>
<ContentPage    xmlns="http://xamarin.com/schemas/2014/forms"
              xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
              xmlns:local="clr-namespace:TriggerDemo"
              x:Class="TriggerDemo.TriggerDemoPage">
  <StackLayout VerticalOptions="Center">
      <Label Text="Do you see colors?"
             VerticalOptions="Center"
             HorizontalOptions="Center" />
      <Entry Placeholder="Type stuff here."
             VerticalOptions="Center"
             HorizontalOptions="Center"
             BackgroundColor="Black">
          <Entry.Triggers>
              <EventTrigger Event="TextChanged" >
                  <local:ColorTriggerAction />
              </EventTrigger>
          </Entry.Triggers>
      </Entry>
  </StackLayout>
</ContentPage>

Requirements

Namespace: Xamarin.Forms
Assembly: Xamarin.Forms.Core (in Xamarin.Forms.Core.dll)
Assembly Versions: 0.0.0.0, 1.3.0.0, 1.4.0.0, 1.5.0.0, 2.0.0.0

The members of Xamarin.Forms.EventTrigger are listed below.

Public Constructors

EventTrigger()

Creates a new EventTrigger instance.

Public Properties

[read-only]	Actions	IList<TriggerAction>. Gets the list of TriggerAction objects that will be invoked when the event that is identified by the EventTrigger.Event property is raised.
	Event	String. Gets or sets the name of the event that will cause the actions that are contained in the EventTrigger.Actions to be invoked.

Protected Methods

override	OnAttached() Internal.
override	OnDetaching() Internal.

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