关于self.view(0,0)点的位置，还有UIScrollView 向下移的问题

前言
朋友问我设置UIScrollView的origin为(0,0)点，但是现实的效果是(0,StatusBar)，就是顶部空出了一个状态栏的高度。我就告诉他添加下面代码，能解决问题。

if (@available(iOS 11, *)) {
      self.scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
 } else {
      self.automaticallyAdjustsScrollViewInsets = NO;
  }

正好就一起扩展一下关于self.View 的(0,0)点的问题

接下来我们看这下面这3个属性

• extendedLayoutIncludesOpaqueBars
• edgesForExtendedLayout
• automaticallyAdjustsScrollViewInsets

1、extendedLayoutIncludesOpaqueBars

1.1如下代码：未设置导航栏的背景

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
//默认导航栏是半透明的
//    [self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"t"] forBarMetrics:UIBarMetricsDefault];
    NSLog(@"extendedLayoutIncludesOpaqueBars = %d",self.extendedLayoutIncludesOpaqueBars);
    
}

打印结果 ： extendedLayoutIncludesOpaqueBars = 0

未设置导航栏背景

1.2 给导航栏设置背景图

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    [self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"t"] forBarMetrics:UIBarMetricsDefault];
    NSLog(@"extendedLayoutIncludesOpaqueBars = %d",self.extendedLayoutIncludesOpaqueBars);
    
}

打印结果：extendedLayoutIncludesOpaqueBars = 0

设置了导航栏背景

小结1：extendedLayoutIncludesOpaqueBars默认为NO，在导航栏为透明的时候，self.view 的(0,0)点，在屏幕的左上角，在导航栏不透明的时候，自动移到导航栏的下方，也就是(0,navigationBarHight)

1.3 导航栏未设置背景图，extendedLayoutIncludesOpaqueBars 赋值为YES

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    self.extendedLayoutIncludesOpaqueBars = YES;
//    [self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"t"] forBarMetrics:UIBarMetricsDefault];
    NSLog(@"extendedLayoutIncludesOpaqueBars = %d",self.extendedLayoutIncludesOpaqueBars);
    
}

打印结果：extendedLayoutIncludesOpaqueBars = 1

导航栏未设置背景图，extendedLayoutIncludesOpaqueBars 赋值为YES

1.4 导航栏设置背景图，extendedLayoutIncludesOpaqueBars 赋值为YES

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    self.extendedLayoutIncludesOpaqueBars = YES;
    [self.navigationController.navigationBar setBackgroundImage:[UIImage imageNamed:@"t"] forBarMetrics:UIBarMetricsDefault];
    NSLog(@"extendedLayoutIncludesOpaqueBars = %d",self.extendedLayoutIncludesOpaqueBars);
    
}

打印结果：extendedLayoutIncludesOpaqueBars = 1

导航栏设置背景图，extendedLayoutIncludesOpaqueBars 赋值为YES

小结2：当设置 extendedLayoutIncludesOpaqueBars = YES的时候，不管导航栏是否透明，self.view的（0，0）点都是屏幕的左上角，我们在开发的时候最好设置为YES ，我们就统一计算frame，方便管理
tip:底部的tabbar也是和navigationBar是一样的道理

2、edgesForExtendedLayout ()

2.1edgesForExtendedLayout 设置为 UIRectEdgeAll(这也是默认值)

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    self.edgesForExtendedLayout = UIRectEdgeAll;
}

UIRectEdgeAll

2.2 edgesForExtendedLayout 设置为 UIRectEdgeTop

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    self.edgesForExtendedLayout = UIRectEdgeTop;
}

UIRectEdgeTop

2.3 edgesForExtendedLayout 设置为 UIRectEdgeBottom

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    self.edgesForExtendedLayout = UIRectEdgeBottom;
}

UIRectEdgeBottom

2.4 edgesForExtendedLayout 设置为 UIRectEdgeNone

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor redColor];
    self.edgesForExtendedLayout = UIRectEdgeNone;
}

UIRectEdgeNone

总结：通过设置edgesForExtendedLayout此属性，你可以指定view的边（上、下、左、右）延伸到整个屏幕。默认为UIRectEdgeAll

3、automaticallyAdjustsScrollViewInsets

automaticallyAdjustsScrollViewInsets（默认YES）这个属性在iOS11 已经被放弃使用了，使用UIScrollView的contentInsetAdjustmentBehavior

automaticallyAdjustsScrollViewInsets

所以我们在使用的时候要兼容老版本，代码如下:

if (@available(iOS 11, *)) {
      self.tableView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
  } else {
      self.automaticallyAdjustsScrollViewInsets = NO;
  }

这个我就不写的Demo了

总结：开发的时候我们就设置 ,让（0，0）点在屏幕的左上角，方便计算frame
self.extendedLayoutIncludesOpaqueBars = YES
if (@available(iOS 11, *)) {
self.tableView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
} else {
self.automaticallyAdjustsScrollViewInsets = NO;
}