iOS核心动画高级技巧二

• 基础视图

UIView *layerView = [[UIView alloc] initWithFrame:CGRectMake(100.0f, 100.0f, 200.0f, 200.0f)];
layerView.backgroundColor = [UIColor whiteColor];
[self.view addSubview:layerView];

• 显示图片

UIImage *image = [UIImage imageNamed:@"test.jpg"];
layerView.layer.contents = (__bridge id _Nullable)(image.CGImage);

• 等比例拉伸以适应图层的边界

layerView.layer.contentsGravity = kCAGravityResizeAspect; 

• contentsScale

layerView.layer.contentsGravity = kCAGravityCenter;
layerView.layer.contentsScale = [[UIScreen mainScreen] scale];

• masksToBounds

layerView.layer.masksToBounds = YES;

• contentsRect 相当于裁剪显示区域(下图显示为整个图片的左上方部分图片)

layerView.layer.contentsRect = CGRectMake(0.0f, 0.0f, 0.5f, 0.5f);

• contentsCenter

layerView.layer.contentsCenter = CGRectMake(0.25, 0.25, 0.5, 0.5);

• 绘图

UIView *layerView = [[UIView alloc] initWithFrame:CGRectMake(100.0f, 100.0f, 200.0f, 200.0f)];
layerView.backgroundColor = [UIColor whiteColor];
[self.view addSubview:layerView];
    
CALayer *blueLayer = [CALayer layer];
blueLayer.frame = CGRectMake(50.0f, 50.0f, 100.0f, 100.0f);
blueLayer.backgroundColor = [UIColor blueColor].CGColor;
[layerView.layer addSublayer:blueLayer];
    
blueLayer.delegate = self;
[blueLayer display];

• CALayerDelegate

- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
{
    CGContextSetLineWidth(ctx, 10.0f);
    CGContextSetStrokeColorWithColor(ctx, [UIColor redColor].CGColor);
    CGContextStrokeEllipseInRect(ctx, layer.bounds);
}