关键帧动画－五角星动画－在层上画出五角星

本例是对核心动画教程的  关键帧动画中的一个例子的一点总结与自己的心得

在.h文件中 定义一个   CGMutablePathRef starPath; 用来纪录当前的路径 以便于绘画。

 

.m文件

- (IBAction)action:(id)sender {
    
    //创建五角星的路径
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathMoveToPoint(path,NULL,240.0, 280.0);
    CGPathAddLineToPoint(path, NULL, 181.0, 99.0);
    CGPathAddLineToPoint(path, NULL, 335.0, 210.0);
    CGPathAddLineToPoint(path, NULL, 144.0, 210.0);
    CGPathAddLineToPoint(path, NULL, 298.0, 99.0);
    CGPathCloseSubpath(path);

    //创建关键帧动画实例
    CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    //关键帧动画定义为10秒，一共6帧，每一帧是10/（6-1）等与2秒
    [animation setDuration:10.0f];
    [animation setDelegate:self];
    [animation setPath:path];


     [self.block.layer addAnimation:animation forKey:NULL];
    
    //在每一帧结束的时候  定时器进入其方法
    [NSTimer scheduledTimerWithTimeInterval:2.0 target:self
                                   selector:@selector(legOne:) userInfo:nil
                                    repeats:NO];
    [NSTimer scheduledTimerWithTimeInterval:4.0
                                     target:self selector:@selector(legTwo:) userInfo:nil
                                    repeats:NO];
    [NSTimer scheduledTimerWithTimeInterval:6.0 target:self
                                   selector:@selector(legThree:) userInfo:nil repeats:NO];
    
    [NSTimer scheduledTimerWithTimeInterval:8.0 target:self selector:@selector(legFour:) userInfo:nil
repeats:NO];
    [NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:@selector(legFive:) userInfo:nil
                                    repeats:NO];
    // Tell the root layer to call drawLayer

    //不设定这个Delegate  调用setNeedDisplay的时候  会不进入 drawLayer方法
    [self.view.layer setDelegate:self];
    
    
    
}

 注意最后一行代码的作用

- (void)legOne:(id)sender {
    CGPathAddLineToPoint(starPath, NULL, 181.0, 99.0);
    [self.view.layer setNeedsDisplay];
}
- (void)legTwo:(id)sender { CGPathAddLineToPoint(starPath, NULL, 335.0, 210.0);
    [self.view.layer setNeedsDisplay];
}
- (void)legThree:(id)sender { CGPathAddLineToPoint(starPath, NULL, 144.0, 210.0);
    [self.view.layer setNeedsDisplay];
}
- (void)legFour:(id)sender { CGPathAddLineToPoint(starPath, NULL, 298.0, 99.0);
    [self.view.layer setNeedsDisplay];
}
- (void)legFive:(id)sender { CGPathCloseSubpath(starPath);
    [self.view.layer setNeedsDisplay];
}

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)context {
   
    CGColorRef white =[UIColor whiteColor].CGColor;
        CGContextSetStrokeColorWithColor(context, white);
    //CFRelease(white);
    CGContextBeginPath(context);
    CGContextAddPath(context, starPath);
    CGContextSetLineWidth(context, 3.0);
    CGContextStrokePath(context);
    NSLog(@"im in drawLayer");
}

 另外 注意  在.h文件中定义的 starPath 要初始化  在ViewDidLoad中完成的

    starPath=CGPathCreateMutable();
    CGPathMoveToPoint(starPath,NULL,240.0, 280.0);