学步园

1.通过添加一个objective-c class,并选择super为 UIView.不同于interface中的view和storyboard.
2.把view controller连接（IBOutlet）到新添加的view。
3.在model中drawRect方法中开始画一个笑脸。
画之前创建了一个画圆的通用方法：

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-(void) drawCircleAtPoint:(CGPoint) p withRadius:(CGFloat) radius inContext:(CGContextRef) context
{
    
    //注意对称封闭 push和pop
    UIGraphicsPushContext(context);
        CGContextBeginPath(context);
        CGContextAddArc(context, p.x, p.y, radius, 0, 2*M_PI, YES);
        CGContextStrokePath(context);
    UIGraphicsPopContext();
}

然后开始画笑脸

- (void)drawRect:(CGRect)rect
{
    // Drawing code
    CGContextRef content =UIGraphicsGetCurrentContext();    //画图都是从这行开始
    //draw face (1 circle)
    CGPoint midPoint;
    
    midPoint.x=self.bounds.origin.x + self.bounds.size.width/2; //屏幕最中心点,因为这里的self.bounds.origin位于(0,0).
    midPoint.y=self.bounds.origin.y + self.bounds.size.height/2;
    
    CGFloat size=self.bounds.size.width/2;
    if(self.bounds.size.height<self.bounds.size.width) size=self.bounds.size.height/2; //根据横竖屏情况取最小半径。
    size *= self.scale; //由getter决定缩放比例

    CGContextSetLineWidth(content, 5.0);
    [[UIColor blueColor] setStroke ];
    [self drawCircleAtPoint:midPoint withRadius:size inContext:content];
    
    
    //eyes (2 circle)
#define EYE_H 0.35
#define EYE_V 0.35
#define EYE_RADIUS 0.15
    CGPoint eyePoint;
    eyePoint.x=midPoint.x-size*EYE_H;   //左眼中心从face中心向左和向上移动。
    eyePoint.y=midPoint.y-size*EYE_V;
    [[UIColor blackColor] setStroke ];
    [self drawCircleAtPoint:eyePoint withRadius:size*EYE_RADIUS inContext:content];
    
    eyePoint.x +=  size*EYE_H*2;        //右眼中心 从左眼位置向右移动到对称位置。
    [self drawCircleAtPoint:eyePoint withRadius:size*EYE_RADIUS inContext:content];
    
    //no nose
    //mouth
#define MOUTH_H 0.45
#define MOUTH_V 0.40
#define MOUTH_SMILE 0.25
    CGPoint mouthStart;
    mouthStart.x=midPoint.x- size *MOUTH_H;//左边嘴角位置
    mouthStart.y=midPoint.y+ size *MOUTH_V;
    
    CGPoint mouthEnd=mouthStart;
    mouthEnd.x +=size *MOUTH_H *2;          //右边嘴角移动到左边嘴角的对称位置
    CGPoint mouthCP1=mouthStart;        
    mouthCP1.x +=size *MOUTH_H *2/3;        //CP(Curve Point)
    CGPoint mouthCP2=mouthEnd;
    mouthCP2.x -=size *MOUTH_H *2/3;
    
    float smile=1;
    CGFloat smileOffset =MOUTH_SMILE * size *smile; //喜哀幅度
    mouthCP1.y+=smileOffset;
    mouthCP2.y+=smileOffset;
    CGContextBeginPath(content);
    CGContextMoveToPoint(content, mouthStart.x, mouthStart.y);//移动到左嘴角
    CGContextAddCurveToPoint(content, mouthCP1.x, mouthCP2.y, mouthCP2.x, mouthCP2.y, mouthEnd.x, mouthEnd.y);
    [[UIColor redColor] setStroke ];
    CGContextStrokePath(content);
  
    
    
}

4.实现drawRect后，在旋转屏幕时需要实现 awakeFromNib而不用重新drawRect.(实际上可以通过面板中的一开关进行设置（mode:Redraw）即可)

-(void) awakeFromNib
{

 　　self.contentMode=UIViewContentModeRedraw;//允许旋转后自动重画

}

但为了不仅让在awakeFromNib中执行，还希望在initWithFrame中执行。原因：（）
因此代码改为：

-(void) setup
{
    self.contentMode=UIViewContentModeRedraw;//允许旋转后自动重画,
}

-(void) awakeFromNib
{
    [self setup];
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        [self setup];
    }
    return self;
}

5.添加缩放scale的setter、getter：

@synthesize scale =_scale;

#define DEFAULT_SCALE 0.90

-(CGFloat) scale
{
    if(!_scale ){
        return DEFAULT_SCALE;
    }else {
        return _scale;
    }
} 

-(void) setScale:(CGFloat)scale
{
    if (scale != _scale) { //高效处理
        _scale=scale;
        [self setNeedsDisplay];
    }
}

6.然后添加手势

-(void) pinch:(UIPinchGestureRecognizer *)gesture
{
    if (gesture.state == UIGestureRecognizerStateChanged || gesture.state == UIGestureRecognizerStateEnded) {
        self.scale *= gesture.scale;//自身view的缩放比例等于手势的缩放比例
        gesture.scale=1;    //这里每次需要重置手势
    }
}