Flex - Event Handling

Flex使用事件的概念將數據從一個對象傳遞到另一個對象，這取決於應用程式中的狀態或用戶交互。

ActionScript有一個泛型的Event類，它定義了處理事件所需的許多功能。每次在Flex應用程式中發生事件時，都會創建事件類層次結構中的三種類型的對象。

事件具有以下三個關鍵屬性

Sr.No	Property & Description
1	類型類型表示剛剛發生的事件類型。這可以是click、initialize、mouseover、change等。實際值將由MouseEvent.click等常量表示。
2	目標 Event的target屬性是對生成事件的組件的對象引用。如果單擊id爲clickMeButton的按鈕，則該單擊事件的目標將是clickMeButton
3	當前目標 currentTarget屬性改變容器層次結構。它主要處理事件流。

Sr.No

Property & Description

類型

類型表示剛剛發生的事件類型。這可以是click、initialize、mouseover、change等。實際值將由MouseEvent.click等常量表示。

目標

Event的target屬性是對生成事件的組件的對象引用。如果單擊id爲clickMeButton的按鈕，則該單擊事件的目標將是clickMeButton

當前目標

currentTarget屬性改變容器層次結構。它主要處理事件流。

Event Flow Phases

一個事件經過三個階段尋找事件處理程序。

Sr.No	Phase & Description
1	capture 在捕獲階段，程序將開始從外部（或頂部）父級到最內部的父級查找事件處理程序。捕獲階段在觸發事件的對象的父級停止。
2	目標在目標階段，會檢查觸發事件的組件是否有事件處理程序。
3	氣泡氣泡階段與捕獲階段相反，從目標組件的父級向上，通過結構反向工作。

Sr.No

Phase & Description

capture

在捕獲階段，程序將開始從外部（或頂部）父級到最內部的父級查找事件處理程序。捕獲階段在觸發事件的對象的父級停止。

目標

在目標階段，會檢查觸發事件的組件是否有事件處理程序。

氣泡

氣泡階段與捕獲階段相反，從目標組件的父級向上，通過結構反向工作。

考慮下面的應用程式代碼−

<?xml version = "1.0" encoding = "utf-8"?>
<s:Application xmlns:fx = "http://ns.adobe.com/mxml/2009" 
   xmlns:s = "library://ns.adobe.com/flex/spark" 
   xmlns:mx = "library://ns.adobe.com/flex/mx
   width = "100%" height = "100%" minWidth = "500" minHeight = "500" >
   
   <s:Panel>
      <s:Button id = "clickMeButton" label = "Click Me!" click = "doAction( );" />
   </s:Panel>   
</s:Application>

當用戶單擊按鈕時，他或她也會單擊面板和應用程式。

事件將經歷三個階段來查找事件處理程序分配。

Let us follow the steps below to test event handing in a Flex application −

Step	Description
1	Create a project with a name HelloWorld under a package com.tutorialspoint.client as explained in the Flex - Create Application chapter.
2	Modify HelloWorld.mxml as explained below. Keep rest of the files unchanged.
3	Compile and run the application to make sure business logic is working as per the requirements.

Following is the content of the modified mxml file src/com.tutorialspoint/HelloWorld.mxml.

<?xml version = "1.0" encoding = "utf-8"?>
<s:Application xmlns:fx = "http://ns.adobe.com/mxml/2009"
   xmlns:s = "library://ns.adobe.com/flex/spark"
   xmlns:mx = "library://ns.adobe.com/flex/mx
   width = "100%" height = "100%" minWidth = "500" minHeight = "500">
   
   <fx:Style source = "/com/tutorialspoint/client/Style.css" />
   <fx:Script>
      <![CDATA[
         protected function reportEvent(event:MouseEvent):void {
            var target:String = event.target.id;
            var currentTarget:String = event.target.id;
            var eventPhase: String;

            if(event.target is Button) {
               var button:Button = event.target as Button;
               target = button.label + " Button";
            } else if(event.target is HGroup) {
               var hGroup:HGroup = event.target as HGroup;
               target = hGroup.id + " HGroup";
            } else if(event.target is Panel) {
               var panel:Panel = event.target as Panel;
               target = panel.id + " Panel";
            }

            if(event.currentTarget is Button) {
               var button1:Button = event.currentTarget as Button;
               currentTarget = button1.label + " Button";
            } else if(event.currentTarget is HGroup) {
               var hGroup1:HGroup = event.currentTarget as HGroup;
               currentTarget = hGroup1.id + " HGroup";
            } else if(event.currentTarget is Panel) {
               var panel1:Panel = event.currentTarget as Panel;
               currentTarget = panel1.id + " Panel";
            }

            var eventPhaseInt:uint = event.eventPhase;

            if(eventPhaseInt == EventPhase.AT_TARGET) {
               eventPhase = "Target";
            } else if(eventPhaseInt == EventPhase.BUBBLING_PHASE) {
               eventPhase = "Bubbling";
            } else if(eventPhaseInt == EventPhase.CAPTURING_PHASE) {
               eventPhase = "Capturing";
            }
            
            reports.text += " Target: " + target + "\n currentTarget: " +
               currentTarget + "\n Phase: " + eventPhase + "\n----------\n";
         }
      ]]>
   </fx:Script>
   
   <s:BorderContainer width = "630" height = "480" id = "mainContainer"
      styleName = "container">
      <s:VGroup width = "100%" height = "100%" gap = "10"
         horizontalAlign = "center" verticalAlign = "middle">
         <s:Label id = "lblHeader" text = "Event Handling Demonstration"
            fontSize = "40" color = "0x777777" styleName = "heading" />

         <s:Panel id = "parentPanel" title = "Main Parent"
            click = "reportEvent(event)" width = "500"
            height = "100" includeInLayout = "true" visible = "true">
            <s:layout>
               <s:VerticalLayout  gap = "10" verticalAlign = "middle"
                  horizontalAlign = "center" />
            </s:layout>
            
            <s:HGroup id = "mainHGroup" click = "reportEvent(event)">
               <s:Button label = "Click Me" click = "reportEvent(event)" />
            </s:HGroup>
         </s:Panel>

         <s:Panel id = "reportPanel" title = "Events" width = "500" height = "230">
            <mx:Text id = "reports" />
         </s:Panel>
      </s:VGroup>
   </s:BorderContainer>
</s:Application>

完成所有更改後，讓我們以正常模式編譯並運行應用程式，就像我們在flex-create application一章中所做的那樣。如果您的應用程式一切正常，它將產生以下結果：[聯機試用]