控制隱藏字幕可見度

您可以控制隱藏字幕的可見度。 當可見性開啟時，會顯示目前選取的軌道。 如果您變更了目前的軌道，可見度設定會維持不變。

public static const HIDDEN:String = hidden;
public static const VISIBLE:String = visible;

1. 等待MediaPlayer至少具有PREPARED狀態（請參閱等待有效狀態）。

2. 若要取得隱藏字幕的目前可見性設定，請使用MediaPlayer中的getter方法，此方法會傳回可見性值。

   public function get ccVisibility():String
   

3. 若要變更隱藏字幕的可見度，請使用setter方法，從ClosedCaptionsVisibility傳遞可見度值。

   例如：

   public function set ccVisibility(value:String):void
   

4. 定義下拉式清單。

   <s:DropDownList id="ccTracksList" width="85"
                   dataProvider="{_ccTracks}"
                   change="onCCTrackChange(event)"
                   prompt="CC"/>
   

5. 定義隱藏字幕軌道的可系結陣列。

   [Bindable] private var _ccTracks:ArrayCollection =
     new ArrayCollection(); // active tracks
   

6. 設定監聽器。

   player.addEventListener(MediaPlayerItemEvent.ITEM_CREATED, onItemCreated);
   player.addEventListener(MediaPlayerItemEvent.CAPTIONS_UPDATED, onCaptionUpdated);
   

   要從銷毀代碼中刪除監聽程式，請執行以下操作：

   player.removeEventListener(MediaPlayerItemEvent.ITEM_CREATED, onItemCreated);
   player.removeEventListener(MediaPlayerItemEvent.CAPTIONS_UPDATED, onCaptionUpdated);
   

7. 當使用者從清單中選擇時，建立並更新清單。

   private function onCCTrackChange(event:IndexChangeEvent):void {
       var ccTrackIndex:int = event.newIndex;
       var ccTracks:Vector.<ClosedCaptionsTrack> =
         _player.currentItem.closedCaptionsTracks;
       if (ccTrackIndex == 0) {
           _player.ccVisibility = MediaPlayer.INVISIBLE;
       }
       else if (ccTrackIndex <= _ccTracks.length) {
           var index:Number = findFromActiveIndex(ccTracks, ccTrackIndex - 1);
           _player.currentItem.selectClosedCaptionsTrack(ccTracks[index]);
           _player.ccVisibility = MediaPlayer.VISIBLE;
       }
   }
   
   private function findFromActiveIndex(ccTracks:Vector.<ClosedCaptionsTrack>,
     ccTrackIndex:int):Number {
       var count:Number = 0;
       for each (var ccTrack:ClosedCaptionsTrack in ccTracks) {
           if (count < ccTrackIndex)
               count = count + 1;
           else
               return count;
       }
       return -1;
   }
   
   private function onItemCreated(event:MediaPlayerItemEvent):void {
       ... (you are likely to need more code here for other reasons)
       updateCCTracks(_player.currentItem.closedCaptionsTracks);
   }
   
   private function onCaptionUpdated(event:MediaPlayerItemEvent):void {
       ... (you are likely to need more code here for other reasons)
       updateCCTracks(_player.currentItem.closedCaptionsTracks,
                     (_player.ccVisibility == MediaPlayer.VISIBLE) ?
                      _player.currentItem.selectedClosedCaptionsTrack : null);
   }
   
   private function updateCCTracks(tracks:Vector.<ClosedCaptionsTrack>,
     selectedTrack:ClosedCaptionsTrack = null):void {
       _ccTracks.removeAll();
   
       _ccTracks.addItem(
           {
               "label": "CC off",
               "data": "cc-off"
           }
       );
   
       var selectedIndex:int = 0;
       for each (var ccTrack:ClosedCaptionsTrack in tracks) {
           _ccTracks.addItem(
               {
                   "label": ccTrack.name,
                   "data": ccTrack.name
               }
           );
           if (selectedTrack && ccTrack.name == selectedTrack.name &&
           ccTrack.language == selectedTrack.language &&
           ccTrack.serviceType == selectedTrack.serviceType) {
               selectedIndex = _ccTracks.length - 1;
           }
       }
   
       var hasCC:Boolean = _ccTracks.length > 0;
       ccTracksList.enabled = hasCC;
       ccTracksList.mouseEnabled = hasCC;
       ccTracksList.selectedIndex = selectedIndex;
   }
   

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