flex4 自定义效果学习

flex4默认提供了很多效果，但是很多时候我们还是要自定义效果才能满足需求

要自定义flex4的效果需要用到两个类，Animate和AnimateInstance

自定义的效果要继承自AnimateInstance，这个类用来编写实际效果运行的代码，里面必须覆盖两个方法play()和animationUpdate()，play()方法用来初始化效果的参数，然后启动效果，animationUpdate()将在效果每次更新过程中调用，这个方法运行的就是实际执行效果的代码。

另一个类继承自Animate，这个类用来自定义效果，但是实际的效果是其内部由AnimateInstance实例来决定的。

下面用一个例子说明如何实现自定义效果

首先定义一个SlideAnimateInstance继承自AnimateInstance，这个类里有两个需要注意的地方，首先是target属性，这个属性表示当前运行效果的对象，另一个是motionPaths属性，这个集合用来存储MotionPath对象，每个MotionPath对象都定义了实际效果运行过程中改变的属性和对应的值。

import flash.display.DisplayObject;
	
	import mx.events.FlexEvent;
	
	import spark.effects.animation.Animation;
	import spark.effects.animation.MotionPath;
	import spark.effects.animation.SimpleMotionPath;
	import spark.effects.supportClasses.AnimateInstance;
	
	/**
	 * 自定义滑动效果 
	 * @author wkkyo
	 * 
	 */	
	public class SlideAnimateInstance extends AnimateInstance
	{
		
		public var direction:String = "up";
		public var offset:Number = 0;
		
		public function SlideAnimateInstance(target:Object){
			super(target);
		}
		
		/**
		 * 覆盖父类的play方法实现自定义效果 
		 * 
		 */		
		override public function play():void{
			//执行效果的组件
			var t:DisplayObject = target as DisplayObject;
			//效果的属性
			var motionPath:SimpleMotionPath = new SimpleMotionPath();
			var from:Number;
			var to:Number;
			
			switch( direction )
			{
				case "up":
					motionPath.property = "y";
					from = -t.height;
					to = offset;
					break;
				case "right":
					motionPath.property = "x";
					from = t.parent.width;
					to = t.parent.width-t.width-offset;
					break;
				case "down":
					motionPath.property = "y";
					from = t.parent.height;
					to = t.parent.height-t.height-offset;
					break;
				case "left":
					motionPath.property = "x";
					from = -t.width;
					to = offset;
					break;
			}
			motionPaths = new Vector.<MotionPath>();
			motionPaths.push(motionPath);
			if (null != triggerEvent ){
				if ( triggerEvent.type == FlexEvent.SHOW ){
					motionPath.valueFrom = from;
					motionPath.valueTo = to;
				}else{
					motionPath.valueFrom = to;
					motionPath.valueTo = from;
				}
			}
			super.play();
		}
		
			
		override public function animationUpdate(animation:Animation):void{
			super.animationUpdate(animation);
			var t:DisplayObject = target as DisplayObject;
			if(direction == "up" || direction == "down"){
				t.y = animation.currentValue["y"] as Number;
			}else if(direction == "left" || direction == "right"){
				t.x = animation.currentValue["x"] as Number;
			}
		}
	}

 

接下来是SlideAnimate继承自Animate，在这个类的构造方法里需要将instanceClass赋值为自定义效果类的实例，即SlideAnimateInstance，同样要覆盖两个方法initInstance()和getAffectedProperties()

import mx.effects.IEffectInstance;
	
	import spark.effects.Animate;
	
	/**
	 * 滑动效果类 
	 * @author wkkyo
	 * 
	 */	
	public class SlideAnimate extends Animate
	{
		/* 组件滑动的方向 “上右下左” */
		[Inspectable(catalog="Common", type="String",enumeration="up,right,down,left", defaultValue = "up" )]
		public var direction:String = "up";
		
		/* 组件偏移量 */
		public var offset:Number = 0;
		
		public function SlideAnimate(target:Object=null)
		{
			super(target);
			instanceClass = SlideAnimateInstance;
		}
		
		
		override protected function initInstance(instance:IEffectInstance):void
		{
			super.initInstance(instance);
			var inst:SlideAnimateInstance = instance as SlideAnimateInstance;
			inst.direction = this.direction;
			inst.offset = this.offset;
		}
		
		
		override public function getAffectedProperties():Array
		{
			return ["x","y"];
		}
	}

 接下来就可以在mxml中使用这个自定义的效果了

<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009" 
					   xmlns:s="library://ns.adobe.com/flex/spark" 
					   xmlns:mx="library://ns.adobe.com/flex/mx" xmlns:effect="com.effect.*">
	<fx:Declarations>
		<!-- 将非可视元素（例如服务、值对象）放在此处 -->
		<effect:SlideAnimate id="slideAnimate" direction="up" />
	</fx:Declarations>
	
	<s:Panel id="pan" title="从上滑出" width="200" height="300" showEffect="{slideAnimate}" hideEffect="{slideAnimate}" >
		
	</s:Panel>
	
	<s:Button label="效果" click="pan.visible=!pan.visible" right="10" />
	
</s:WindowedApplication>

 其他效果都是类似的，重点就是在play方法中设置效果的参数，然后在animationUpdate修改对应的属性。