cocos2D创建一组单选按钮菜单

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看了一下CCMenu类的实现，主要包含以下几个关键参数：

selected_成员变量，配合selected和unselected方法设置CCMenuItemImage中SelectedItemImage是否显示。
state_成员变量有2种状态，当TouchBegan的时候设置为Tracking状态，TouchEnd的时候设置为Waiting状态。
activate方法使得当前CCMenuItem获得焦点，真正的被选中。
CCMenuItem *curSelection = [self itemForTouch:touch];该变量用来记录当前touch的CCMenuItem

创建一个CCRadioMenu类继承自CCMenu类

1. curHightLighted_ 成员变量，表示当前选中的Item

CCRadioMenu.m文件主要内容如下：

- (void)setSelectedItem: (CCMenuItem *)item{    [selectedItem_ unselected];    selectedItem_ = item;    [selectedItem_ selected];}

-(BOOL) ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event{if( state_ != kCCMenuStateWaiting || !visible_ )return NO;CCMenuItem *curSelection = [self itemForTouch:touch];    [curSelection selected];    _curHightlighted = curSelection;        if (_curHightlighted) {        if (selectedItem_ != curSelection) {            [selectedItem_ unselected];                        state_ = kCCMenuStateTrackingTouch;            return YES;        }    }return NO;}-(void) ccTouchEnded:(UITouch *)touch withEvent:(UIEvent *)event{NSAssert(state_ == kCCMenuStateTrackingTouch, @"[Menu ccTouchEnded] -- invalid state");    CCMenuItem *curSelection = [self itemForTouch:touch];        if (curSelection) {        if (curSelection != _curHightlighted) {            [_curHightlighted unselected];            selectedItem_ = curSelection;            [selectedItem_ selected];            [selectedItem_ activate];            _curHightlighted = nil;            state_ = kCCMenuStateWaiting;            return;        }    }    [selectedItem_ unselected];    selectedItem_ = _curHightlighted;    [selectedItem_ selected];    [selectedItem_ activate];    _curHightlighted = nil;state_ = kCCMenuStateWaiting;}

用法如下：

    CCRadioMenu *radioMenu = [CCRadioMenu menuWithItems:menuItem1, menuItem2, menuItem3, nil];    [radioMenu setSelectedItem:menuItem1];    [radioMenu alignItemsVerticallyWithPadding:(20.0/480)*winSize.height];    radioMenu.position = ccp(winSize.width/2, winSize.height/2);    [self addChild:radioMenu z:2];