ios之如何让图片显示成圆形的样式/设置控件边框大小以及颜色

比如说QQ登陆头像显示出来的就是圆形的，但实际上它的图片并非就是圆形，而是通过对layer层进行绘制而成的。说到layer每个控件都会有layer层属性所以可以把任意的控件都可以设置成圆形，或是椭圆型看项目需要而定

 UIImageView *imageView = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"头像.png"]];
    imageView.frame = CGRectMake(100, 100, 100, 100);
    // 通过layer层设置控件的边角半径（每个控件都会有一个layer层所有其他控件也都能实现圆形效果）
    imageView.layer.cornerRadius = 50;
    // 同时也要设置超出部分不让显示 这样就可以达到一个圆形的效果图片-
    imageView.clipsToBounds = YES;
    
    [mainView.view addSubview:imageView];

下面是苹果API

@property CGFloat cornerRadius; //设置边角半径

/* The width of the layer's border, inset from the layer bounds. The
 * border is composited above the layer's content and sublayers and
 * includes the effects of the `cornerRadius' property. Defaults to
 * zero. Animatable. */

@property CGFloat borderWidth; // 设置控件的边框宽度

/* The color of the layer's border. Defaults to opaque black. Colors
 * created from tiled patterns are supported. Animatable. */

@property CGColorRef borderColor;  // 设置控件的边框颜色

/* The opacity of the layer, as a value between zero and one. Defaults
 * to one. Specifying a value outside the [0,1] range will give undefined
 * results. Animatable. */

@property float opacity; // 设置控件的透明度有部分动画会用到

/* When true, and the layer's opacity property is less than one, the
 * layer is allowed to composite itself as a group separate from its
 * parent. This gives the correct results when the layer contains
 * multiple opaque components, but may reduce performance.
 *
 * The default value of the property is read from the boolean
 * UIViewGroupOpacity property in the main bundle's Info.plist. If no
 * value is found in the Info.plist the default value is YES for
 * applications linked against the iOS 7 SDK or later and NO for
 * applications linked against an earlier SDK. */

// 只需要这两句话就可以设置完成
    imageView.layer.borderWidth = 2; // float类型数据
    imageView.layer.borderColor = [UIColor redColor].CGColor;  // 颜色需要是CGColor