1、带xib控制器加载过程

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
}
- (IBAction)btnClicked:(UIButton *)sender {
    //如果只执行init，它会执行initWithNibName:bundle:方法，并且参数都为空
    EOCViewController * vc = [[EOCViewController alloc] init];
    //当nibName参数为nil，表示加载名为EOCViewController的对象，如果bundle为空，表示在主路径下寻找xib文件
    //EOCViewController * vc = [[EOCViewController alloc] initWithNibName:@"EOCViewController" bundle:nil];
    [self presentViewController:vc animated:YES completion:^{
        
    }];
}
@end

@implementation EOCViewController
- (instancetype)init{
    NSLog(@"%s",__func__);
    self = [super init];
    return self;
}
- (instancetype)initWithCoder:(NSCoder *)aDecoder{
    NSLog(@"%s",__func__);
    self = [super initWithCoder:aDecoder];
    return self;
}
- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil{
   NSLog(@"%s",__func__);
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    return self;
}
@end

结果：

-[EOCViewController init]
-[EOCViewController initWithNibName:bundle:]
-[EOCViewController viewDidLoad]

2、带xib文件，重写loadView方法。不会加载出来这个xib文件。如果不重写这个loadView方法，加载xib的时候会自动加载此方法。如：EOCViewController控制器。

- (void)loadView{
    NSLog(@"%s",__func__);
    [super loadView];
}

3、如果去掉EOCViewController控制器的xib文件，执行如下代码：

- (void)loadView{
    NSLog(@"%s",__func__);
//    [super loadView];
}
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"%s",__func__);
    self.view.backgroundColor = [UIColor whiteColor];
}

会造成loadView与viewDidLoad方法循环调用。原因是self.view是懒加载方法:

- (UIView *)view{
    if (!_view) {
        [self loadView];
        [self viewDidLoad];
    }
    return _view;
}

4、在xib中加载视图控制器，self.view是在viewDidAppear中加载完的（frame为屏幕的大小），而不是在viewDidLoad中加载完的（frame为xib的大小），所以self.view的frame大小还没有在viewDidLoad中成型。
不带xib的控制器被加载，viewDidLoad方法中frame的为手机屏幕的大小。
5、通过重写loadView改变控制器的视图.

- (void)loadView{
    NSLog(@"%s",__func__);
    [super loadView];
    self.view = [[NSBundle mainBundle] loadNibNamed:@"EOCView" owner:self options:nil].lastObject;
}
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"%s",__func__);
    self.view.backgroundColor = [UIColor whiteColor];
}

6、视图加载过程
EOCView * view = [[NSBundle mainBundle]loadNibNamed:@"EOCView" owner:self options:nil].lastObject;启动过程：

initWithCoder:
awakeFromNib:

EOCView * view = [[EOCView alloc] init];启动过程：

init
initWithFrame:

init方法中会封装initWithFrame:方法。
7、在initWithFrame:方法中添加视图。

#import "ECOLabel.h"
@implementation ECOLabel
- (instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if (self) {
        UIView * view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
        
        view.backgroundColor = [UIColor blueColor];
        [self addSubview:view];
    }
    return self;
}
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor lightGrayColor];
    ECOLabel * lbl = [[ECOLabel alloc] initWithFrame:CGRectMake(0, 0, 90, 90)];
    lbl.backgroundColor = [UIColor yellowColor];
//    lbl.backgroundColor = [UIColor clearColor];
    [self.view addSubview:lbl];
}

会出现如下如图一效果：

ECOLabel对象背景色为黄色 图一.png

ECOLabel对象背景色为透明色 图二.png

IB_DESIGNABLE
@interface EOCView ()
@property (nonatomic, strong) IBInspectable UIColor * pathColor;
@property (nonatomic, assign) IBInspectable CGFloat pathWith;
@end

- (void)drawRect:(CGRect)rect{
    [super drawRect:rect];
    CGFloat centerX = (self.bounds.size.width - self.bounds.origin.x) / 2;
    CGFloat centerY = (self.bounds.size.height - self.bounds.origin.y) / 2;
    
    UIBezierPath * path = [[UIBezierPath alloc] init];
    //添加一个圆形
    [path addArcWithCenter:CGPointMake(centerX, centerY) radius:50 startAngle:0 endAngle:360 clockwise:YES];
    //设置宽度
    path.lineWidth = self.pathWith;
    //设置线条颜色
    [self.pathColor setStroke];
    //绘制线条
    [path stroke];
}

效果如图三所示。

视图关联EOCView对象加入控制器的XIB中 图三.png