在开发中，现在很多app更新了新功能时都会给出用户一个提示，以方便用户更好的体验，那么这个功能如何实现的呢？
首先看下效果图：

1.首先创建第一个viewcontroller 在上面放上一个imageview和一个按钮

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    UIImageView *imageview=[[UIImageView alloc]init];
    imageview.frame=CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height);
    imageview.image=[UIImage imageNamed:@"girl.png"];
    [self.view addSubview:imageview];

    UIButton *Btn=[[UIButton alloc]init];
    Btn.frame=CGRectMake(20, 100, 50, 50);
    Btn.backgroundColor=[UIColor blueColor];
    [Btn addTarget:self action:@selector(btnclick) forControlEvents:UIControlEventTouchUpInside];

    [imageview addSubview:Btn];
    imageview.userInteractionEnabled=YES;


}
-(void)btnclick
{
    BackViewController *backVc=[[BackViewController alloc]init];


    [self presentViewController:backVc animated:YES completion:nil];
}

2.这时候我们在创建一个BackViewController 设置透明即可

- (instancetype)init
{
    self = [super init];
    if (self) {


        self.view.backgroundColor=[UIColor colorWithWhite:0 alpha:0.4];
        self.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
        self.modalPresentationStyle = UIModalPresentationOverFullScreen;
    }
    return self;
}

这里提示一点，很多时候我们对视图直接设置alpha属性的值会导致其子控件也变得半透明，而通常我们的需求是：背景半透明而其子控件不透明。
因此我们可以用一下方法设置透明度

//只设置黑白背景色 white后面的参数表示灰度，从0-1之间表示从黑到白的变化，alpha就是你想调整的透明度。
    blackV.backgroundColor = [UIColor colorWithWhite:0.f alpha:0.7];  


//设置任意颜色的背景色
blackV.backgroundColor = [UIColor colorWithRed:122/255.0 green:123/255.0 blue:234/255.0 alpha:0.7]; 

UIColor *color = [UIColor blackColor];
bgView.backgroundColor = [color colorWithAlphaComponent:0.5];

3.设置BackViewController上面的控件

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *btn=[UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame=CGRectMake(50, 300, 50, 50);
//    btn.backgroundColor=[UIColor blueColor];
    [self.view addSubview:btn];
    [btn setBackgroundImage:[UIImage imageNamed:@"userGuideBtnBG_unClear.png"] forState:UIControlStateNormal];
    [btn addTarget:self action:@selector(btnclick) forControlEvents:UIControlEventTouchUpInside];
    btn.backgroundColor=[UIColor clearColor];
    btn.alpha=0.75;

    UIView *view1=[[UIView alloc]init];
    view1.backgroundColor=[UIColor blackColor];
    view1.alpha=0.75;
    [self.view addSubview:view1];
    view1.frame=CGRectMake(0, 0, self.view.frame.size.width, 300);

    UIView *view2=[[UIView alloc]init];
    view2.backgroundColor=[UIColor blackColor];
    view2.alpha=0.75;
    [self.view addSubview:view2];
    view2.frame=CGRectMake(0, 300+50, self.view.frame.size.width, self.view.frame.size.height-50-300);

    UIView *view3=[[UIView alloc]init];
    view3.backgroundColor=[UIColor blackColor];
    view3.alpha=0.75;
    [self.view addSubview:view3];
    view3.frame=CGRectMake(0, 300, 50, 50);

    UIView *view4=[[UIView alloc]init];
    view4.backgroundColor=[UIColor blackColor];
    view4.alpha=0.75;
    [self.view addSubview:view4];
    view4.frame=CGRectMake(50+50, 300, self.view.frame.size.width-50-50, 50);


    UILabel *titlelabel=[[UILabel alloc]init];
    titlelabel.frame=CGRectMake(100, 350,100,50 );
    [self.view addSubview:titlelabel];
    titlelabel.text=@"这是新功能";
    titlelabel.textColor=[UIColor whiteColor];

}
-(void)btnclick
{
    [self dismissViewControllerAnimated:YES completion:nil];
}

原理很简单，我们present出来一个透明的控制器，这样在控制器上面放上几个深度alpha的view和一个btn，哦，还需要一个label提示文字，也可以自己再添加一些箭头什么的，当然这个btn时美工扣图处理之后给你的，然后通过改变它们的frame来实现不同位置的提示。因为是做的demo所以我用了frame，我建议用autolayout去定它们之间的关系，然后用transform来实现移动frame，然后可以提示多个新功能。
btn抠图之后的效果：