1.File’s Owner为nil

    UIView *demo1 = [[[NSBundle mainBundle] loadNibNamed:@"demo1" owner:nil options:nil] lastObject];

    CGRect rect = demo1.frame;

    rect.origin.y = 100;

    demo1.frame = rect;

    [self.view addSubview:demo1];

2.File’s Owner有值,　File’s Owner可以是任何实例,不一定是控制器

　 // 下面是demo2_class1.h, xib和demo2_class1连线产生的

　 @property (weak, nonatomic) IBOutlet UIView *purpleView;

　 @property (weak, nonatomic) IBOutlet UIView *blueView;

    // 下面是mainViewController.m

　 demo2_class1 *demo2 = [[demo2_class1 alloc]init];

    NSLog(@"load前:demo2.purpleView.frame-------%@",NSStringFromCGRect(demo2.purpleView.frame));

    NSLog(@"load前:demo2.blueView.frame-------%@",NSStringFromCGRect(demo2.blueView.frame));

    // 此时self.view是没值的,也就是说往self.view上加东西,是不会有效果的

    // [self.view addSubview:demo2.purpleView];

    [[[NSBundle mainBundle] loadNibNamed:@"demo2" owner:demo2 options:nil] lastObject];

    NSLog(@"load后:demo2.purpleView.frame-------%@",NSStringFromCGRect(demo2.purpleView.frame));

    NSLog(@"load后:demo2.blueView.frame-------%@",NSStringFromCGRect(demo2.blueView.frame));

    [self.view addSubview:demo2.purpleView];

说明:xib只有loadNib完之后,File’s Owner的IBOutlet才会自动初始化

3.  如果在<2>的代码的基础上,新建一个dog类,把Owner改成dog,其他都不改

　 Dog *dog = [[Dog alloc]init];

    [[[NSBundle mainBundle] loadNibNamed:@"demo2" owner:dog options:nil] lastObject];

运行程序,程序崩溃,崩溃原因如下,由此可见,在loadNibNamed时,会去找owner的IBOutlet,并对IBOutlet做setValue的操作

2015-02-03 14:49:17.285 xib开发[31342:60b] *** Terminating app due to uncaught exception ‘NSUnknownKeyException‘, reason: ‘[<Dog 0x8d4bc90> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key blueView.‘

4.如果在<2>的代码的基础上,给demo2_classs1这个类添加实例方法 - (IBAction)clickMe;并且在xib上添加个按钮,按钮和clickMe做连线

在模拟器上点击那个按钮,有打印.

5.xib里的view指定为自定义的类.  PS:File’s Owner不用去设

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5.1 Demo3 class一般是自定义类,需要提供一个遍历构造方法,方便使用

+ (instancetype)initWithXib{

    return [[[NSBundle mainBundle] loadNibNamed:@"demo3" owner:nil options:nil] lastObject];

}

5.2 补充:如果需要对xib里各个子控件做个性化的设置,可以在awakeFromNib做相应设置

- (void)awakeFromNib{

    self.backgroundColor = [UIColor redColor];

}

5.3 在mainViewController.m里使用xib

    demo3_class *demo3 = [demo3_class initWithXib];

    CGRect rect = demo3.frame;

    rect.origin.y = 200;

    demo3.frame = rect;

    [self.view addSubview:demo3];

6.xib的File’s Owner是UIViewController的子类,File’s Owner的view 就是xib的view

// 提供便捷方法

+ (instancetype)viewControllerFromXib{

    return [[self alloc] initWithNibName:@"demo4" bundle:nil];

}

看看MainViewController怎么使用:

　 // 稳妥的做法

　 demo4_ViewController *demo4VC = [[demo4_ViewController alloc]initWithNibName:@"demo4" bundle:nil];

　 // 或者用便捷方法,如果xib文件的名字和类名称一样,可以用便捷方法

　 // demo4_ViewController *demo4VC = [demo4_ViewController demo4ViewController];

    [self.view addSubview:demo4VC.view];

　 // 父子控制器

　 [self addChildViewController:demo4VC];

iOS xib的使用详解