SetNeedsLayout

这个方法和SetNeedsDisplay非常相似，并且也是CALayer 和 UIView都有的同名方法，我们在上篇认识了：layoutSubViews 这个方法，对应的，层Layer拥有layoutSublayers的相似方法。根据文档：

“发动触发在下一个更新循环中更新布局，在主线程中调用，并集中在同一个更新周期，旨在提高性能“ 

和SetNeedsDisplay方法一样，这个方法也是专门为layoutSubViews服务的。

UIView

头文件：

#import <UIKit/UIKit.h>

@interface LBSetNeedsLayoutViewController : UIViewController

@end

#pragma mark - LBSetNeedsLayoutView

@interface LBSetNeedsLayoutView : UIView

@property (nonatomic, assign) BOOL isChangeTheBackgroundColor;

@end

实现文件：

#import "UIColor+RandomColor.h"
#import "LBSetNeedsLayoutViewController.h"

@interface LBSetNeedsLayoutViewController ()

@property (nonatomic, strong) LBSetNeedsLayoutView* setNeedsLayoutView;

@end

@implementation LBSetNeedsLayoutViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.setNeedsLayoutView = [[LBSetNeedsLayoutView alloc] init];
    [self.setNeedsLayoutView setFrame:CGRectMake(0, 0, 100, 100)];
    [self.setNeedsLayoutView setBackgroundColor:[UIColor randomColor]];
    [self.view addSubview:self.setNeedsLayoutView];
    
    UIButton* button = [UIButton buttonWithType:UIButtonTypeCustom];
    [button setFrame:CGRectMake(0, 0, 50, 50)];
    [button setCenter:CGPointMake(self.view.center.x, button.center.y + 50)];
    [button setBackgroundColor:[UIColor blueColor]];
    [button addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}


- (void)buttonClicked:(id)sender
{
    [self.setNeedsLayoutView setIsChangeTheBackgroundColor:YES];
    
    [self.setNeedsLayoutView setNeedsLayout];
}

 @end


#pragma mark - LBSetNeedsLayoutView


@implementation LBSetNeedsLayoutView

- (id)init
{
    self = [super init];
    
    if (self)
    {
        _isChangeTheBackgroundColor = NO;
    }
    
    return self;
}

- (void)layoutSubviews
{
    [super layoutSubviews];
    
    if (_isChangeTheBackgroundColor)
    {
        [self setBackgroundColor:[UIColor randomColor]];
    }
    
    NSLog(@" Test setNeedsLayout RelationShip.. ");
}

@end

CALayer

头文件：

#import <UIKit/UIKit.h>

@interface LBSetNeedsLayoutLayerController : UIViewController

@end

#pragma mark - LBSetNeedsLayoutLayer

@interface LBSetNeedsLayoutLayer : CALayer

@property (nonatomic, assign) BOOL isChangeTheBackgroundColor;

@end

实现文件：

#import "UIColor+RandomColor.h"
#import "LBSetNeedsLayoutLayerController.h"

@interface LBSetNeedsLayoutLayerController ()

@property (nonatomic, strong) LBSetNeedsLayoutLayer* setNeedsLayoutLayer;

@end

@implementation LBSetNeedsLayoutLayerController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.setNeedsLayoutLayer = [LBSetNeedsLayoutLayer layer];
    [self.setNeedsLayoutLayer setBackgroundColor:[UIColor randomColor].CGColor];
    [self.setNeedsLayoutLayer setBounds:CGRectMake(0, 0, 150, 150)];
    [self.view.layer addSublayer:self.setNeedsLayoutLayer];
    
    
    UIButton* button = [UIButton buttonWithType:UIButtonTypeCustom];
    [button setFrame:CGRectMake(0, 0, 50, 50)];
    [button setCenter:CGPointMake(self.view.center.x, self.view.center.y)];
    [button setBackgroundColor:[UIColor yellowColor]];
    [button addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}

- (void)buttonClicked:(id)sender
{
    [self.setNeedsLayoutLayer setIsChangeTheBackgroundColor:YES];
    
    [self.setNeedsLayoutLayer setNeedsLayout];
}

@end


#pragma mark - LBSetNeedsLayoutLayer

@implementation LBSetNeedsLayoutLayer

- (void)layoutSublayers
{
    [super layoutSublayers];
    
    if (_isChangeTheBackgroundColor)
    {
        [self setBackgroundColor:[UIColor randomColor].CGColor];
    }
    
    NSLog(@"setNeedsLayout invokes layoutSublayers");
}

@end

有些人会疑问，那这两者究竟区别是什么呢？其实很显然了，一个是视图重绘，一个是针对子视图的布局更新

http://stackoverflow.com/questions/14506968/setneedslayout-and-setneedsdisplay