根据进度条来设置图片的透明度

{
    UISwitch *switc;
    UISlider *slide;
    UIImageView *imgView;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    self.view.backgroundColor = [UIColor whiteColor];
    self.title = @"日考7";
    
    switc = [[UISwitch alloc]initWithFrame:CGRectMake(self.view.frame.size.width / 2 - 25, 100, 100, 50)];
    switc.on = YES;//设置初始为on的一边
    [switc addTarget:self action:@selector(switchAction:) forControlEvents:UIControlEventValueChanged];   // 开关事件切换通知
    [self.view addSubview:switc];
    
    imgView = [[UIImageView alloc]initWithFrame:CGRectMake(self.view.frame.size.width / 2 - 150, 250, 300, 300)];
    imgView.backgroundColor = [UIColor redColor];
    [self.view addSubview:imgView];
    
    slide = [[UISlider alloc]initWithFrame:CGRectMake(self.view.frame.size.width / 2 - 100, 650, 200, 20)];
    slide.minimumValue = 0;// 设置最小值
    slide.maximumValue = 1;// 设置最大值
    slide.continuous = YES;// 设置可连续变化
    slide.value = slide.maximumValue;// 设置初始值
    [slide addTarget:self action:@selector(sliderValueChanged:) forControlEvents:UIControlEventValueChanged];// 针对值变化添加响应方法
    [self.view addSubview:slide];
    
}
- (void)sliderValueChanged:(id)sender{
    NSLog(@"滑动条");
    imgView.alpha = slide.value;
}

-(void)switchAction:(id)sender{
    NSLog(@"点击了开关");
    if (switc.on == NO) {
        slide.hidden = YES;
    }
    else{
    slide.hidden = NO;
    }
}