ios入门第一课

@interface ViewController (){
//设置便签
BOOL _btn;
}

@end

@implementation ViewController

- (void)viewDidLoad {
[super viewDidLoad];
//定义并初始化一个按钮
UIButton *btn =[[UIButton alloc]init];
// 设置按钮的位置和长宽
[btn setFrame:CGRectMake(160.0, 274, 100, 100)];
//设置初始颜色
[btn setBackgroundColor:[UIColor redColor]];
//绑定点击事件
[btn addTarget:self action:@selector(btnclick:)forControlEvents:UIControlEventTouchUpInside];
//把按钮添加到视图中
[self.view addSubview:btn];

}

- (void)btnclick:(UIButton *)button {
button.selected = !(_btn);
if (button.selected) {
button.backgroundColor = [UIColor blueColor];
_btn = YES;
} else {
button.backgroundColor = [UIColor redColor];
_btn = NO;
}
}