014改变背景颜色（扩展知识：两个圆角的视图）

效果如下：

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController {
    @private
    UILabel *lblMessage;
    CGFloat colorRed;
    CGFloat colorGreen;
    CGFloat colorBlue;
}

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()
- (void)redDidPush;
- (void)greenDidPush;
- (void)blueDidPush;
- (void)changeLabelColor:(CGFloat*)pColor;
@end

@implementation ViewController

#pragma mark - Start Implementation For Methods
- (void)viewDidLoad {
    [super viewDidLoad];
    colorRed = 0.0;
    colorGreen = 0.0;
    colorBlue = 0.0;
    CGPoint newPoint = self.view.center;
    
    //追加Label标签
    lblMessage = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 320, 200)];
    lblMessage.textAlignment = NSTextAlignmentCenter;
    lblMessage.center = newPoint;
    lblMessage.textColor = [UIColor whiteColor];
    lblMessage.text = @"染上新的颜色吧...";
    lblMessage.backgroundColor = [[UIColor alloc] initWithRed:colorRed green:colorGreen blue:colorBlue alpha:1.0];
    //设置Label标签的圆角
    //默认是四个圆角
//    lblMessage.layer.cornerRadius = 20.0;
//    lblMessage.layer.masksToBounds = YES;
    
    /*
     typedef NS_OPTIONS(NSUInteger, UIRectCorner) {
     UIRectCornerTopLeft     = 1 << 0,
     UIRectCornerTopRight    = 1 << 1,
     UIRectCornerBottomLeft  = 1 << 2,
     UIRectCornerBottomRight = 1 << 3,
     UIRectCornerAllCorners  = ~0UL
     };
     */
    //这里使用Layer实现两个圆角；左上角和右上角
    UIRectCorner rectCorner = UIRectCornerTopLeft | UIRectCornerTopRight;
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:lblMessage.bounds
                                               byRoundingCorners:rectCorner
                                                     cornerRadii:CGSizeMake(20.0, 20.0)];
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.path = path.CGPath;
    lblMessage.layer.mask = shapeLayer;
    [self.view addSubview:lblMessage];
    
    //追加红色按钮
    UIButton *btnRed = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    btnRed.frame = CGRectMake(0, 0, 50, 40);
    newPoint.x -= (btnRed.frame.size.width + 10);
    newPoint.y = self.view.frame.size.height - 70;
    btnRed.center = newPoint;
    btnRed.backgroundColor = [UIColor grayColor];
    [btnRed setTitle:@"红" forState:UIControlStateNormal];
    [btnRed setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    [btnRed addTarget:self action:@selector(redDidPush) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btnRed];
    
    //追加绿色按钮
    UIButton *btnGreen = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    btnGreen.frame = btnRed.frame;
    newPoint.x += (btnRed.frame.size.width + 5);
    btnGreen.center = newPoint;
    btnGreen.backgroundColor = [UIColor grayColor];
    [btnGreen setTitle:@"绿" forState:UIControlStateNormal];
    [btnGreen setTitleColor:[UIColor greenColor] forState:UIControlStateNormal];
    [btnGreen addTarget:self action:@selector(greenDidPush) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btnGreen];
    
    //追加蓝色按钮
    UIButton *btnBlue = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    btnBlue.frame = btnRed.frame;
    newPoint.x += (btnRed.frame.size.width + 5);
    btnBlue.center = newPoint;
    btnBlue.backgroundColor = [UIColor grayColor];
    [btnBlue setTitle:@"蓝" forState:UIControlStateNormal];
    [btnBlue setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [btnBlue addTarget:self action:@selector(blueDidPush) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btnBlue];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Private Methods
- (void)redDidPush {
    [self changeLabelColor:&colorRed];
}

- (void)greenDidPush {
    [self changeLabelColor:&colorGreen];
}

- (void)blueDidPush {
    [self changeLabelColor:&colorBlue];
}

- (void)changeLabelColor:(CGFloat*)pColor {
    if (pColor) {
        if (*pColor > 0.99) {
            *pColor = 0.0;
        } else {
            *pColor += 0.1;
        }
        lblMessage.backgroundColor = [[UIColor alloc] initWithRed:colorRed green:colorGreen blue:colorBlue alpha:1.0];
    }
}

@end