[转] 解析LayoutSubviews

//
//  TestView.h
//  LayoutSubviews
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface TestView : UIView

@end

//
//  TestView.m
//  LayoutSubviews
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import "TestView.h"

@implementation TestView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
        NSLog(@"initWithFrame:%@" ,NSStringFromCGRect(frame));
    }
    return self;
}

- (void)layoutSubviews
{
    NSLog(@"layoutSubviews %@", self);
    [super layoutSubviews];
}

@end

//
//  RootViewController.m
//  LayoutSubviews
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import "RootViewController.h"
#import "TestView.h"

@interface RootViewController ()

@property (nonatomic, strong) NSTimer   *timer;
@property (nonatomic, strong) TestView  *largeView;
@property (nonatomic, strong) TestView  *smallView;

@end

@implementation RootViewController


- (void)viewDidLoad
{
    [super viewDidLoad];

    // 1、init初始化不会触发layoutSubviews [正确的]
    // 2、addSubview会触发layoutSubviews [不完全正确,当frame为0时是不会触发的]
    // 3、设置view的Frame会触发layoutSubviews，当然前提是frame的值设置前后发生了变化 [正确]
    
//    [self test_1];
//    [self test_2];
//    [self test_3];
    
    // 4、滚动一个UIScrollView会触发layoutSubviews[错误,不用滚动就会触发]
//    [self test_4];
    
    // 5、改变一个UIView大小的时候也会触发父UIView上的layoutSubviews事件
    [self test_5];
}


- (void)test_1
{
    /* 
     解释:
     
     走了initWithFrame:方法,但是又有frame值为{{0, 0}, {0, 0}},并不需要绘制任何的东西,
     所以即使添加了test,也没必要绘制它,同时也验证了addSubview会触发layoutSubviews是错
     误的,只有当被添加的view有着尺寸的时候才会触发layoutSubviews
     */
    
    TestView *test = [TestView new];
    [self.view addSubview:test];
}

- (void)test_2
{
    TestView *test = [TestView new];
    test.frame = CGRectMake(0, 0, 100, 100);
    [self.view addSubview:test];
}

- (void)test_3
{
    /*
     解释:
     
     layoutSubviews这个方法自身无法调用,是被父类添加的时候才执行的方法
     */
    
    TestView *test = [TestView new];
    test.frame = CGRectMake(0, 0, 50, 50);
    UIView *showView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];
    [test addSubview:showView];
}

- (void)test_4
{
    CGRect rect    = self.view.bounds;
    CGFloat height = rect.size.height;
    CGFloat width  = rect.size.width;
    
    UIScrollView *rootScroll = [[UIScrollView alloc] initWithFrame:self.view.bounds];
    NSArray *data            = @[@"", @"", @"", @""];
    [data enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        TestView *tmp        = [[TestView alloc] initWithFrame:CGRectMake(width*idx, 0,
                                                                          width, height)];
        [rootScroll addSubview:tmp];
    }];
    rootScroll.contentSize   = CGSizeMake(width * data.count, height);
    [self.view addSubview:rootScroll];
}

- (void)test_5
{
    _timer = [NSTimer scheduledTimerWithTimeInterval:1.f
                                              target:self
                                            selector:@selector(timerEvent:)
                                            userInfo:nil
                                             repeats:YES];
    _largeView = [[TestView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:_largeView];
    
    _smallView = [[TestView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
    [_largeView addSubview:_smallView];
}

- (void)timerEvent:(id)sender
{
    _smallView.frame = CGRectMake(arc4random()%100 + 20,
                                  arc4random()%100 + 20,
                                  arc4random()%100 + 20,
                                  arc4random()%100 + 20);
    NSLog(@"_smallView %@", _smallView);
    NSLog(@"_smallView %@", _largeView);
}

@end