对于UI控件，我们创建一个新项目，类别是IOS类下的Applicatin中的Single View Application。

UILabel

UILable是iPhone界面最基本的控件，主要用来显示文本信息。
修改项目中的ViewController.m文件，达到创建UILable，设置其中的显示内容，字体大小颜色，阴影，字体对齐方式，显示行数等。

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #d12f1b}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; min-height: 13.0px}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #4f8187}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #bb2ca2}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo}p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #008400}p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'Heiti SC Light'; color: #008400}p.p8 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #703daa}p.p9 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #3d1d81}span.s1 {font-variant-ligatures: no-common-ligatures; color: #78492a}span.s2 {font-variant-ligatures: no-common-ligatures}span.s3 {font-variant-ligatures: no-common-ligatures; color: #bb2ca2}span.s4 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s5 {font: 11.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures}span.s6 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures; color: #000000}span.s7 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures}span.s8 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s9 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s10 {font-variant-ligatures: no-common-ligatures; color: #272ad8}

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

//创建UI控件
-(void)createUI
{
    //定义并创建一个UI Label
    //UILabel可以显示在屏幕上的，并且可以显示文字的UI控件
    UILabel* label=[[UILabel alloc]init];
    
    label.text=@"hello world!bababababkkkkk";
    label.frame=CGRectMake(100, 150, 160, 90);
    label.backgroundColor=[UIColor redColor];
    [self.view addSubview:label];
    
    //设置字体大小颜色
    label.font=[UIFont systemFontOfSize:22];
    label.textColor=[UIColor blackColor];
    
    //设置阴影颜色
    label.shadowOffset=CGSizeMake(5, 10);
    label.shadowColor=[UIColor grayColor];
    
    //文字对齐方式
    label.textAlignment=NSTextAlignmentCenter;
    
    //文字显示行数，默认为1 如果值为0 即按需要显示
    label.numberOfLines=3;
    
}

UIButton

修改项目中的ViewController.m文件，达到创建按钮，设置文字内容和风格，按钮事件等效果：

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'Heiti SC Light'; color: #008400}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #3d1d81}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; min-height: 13.0px}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #008400}p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #703daa}p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #d12f1b}span.s1 {font-variant-ligatures: no-common-ligatures}span.s2 {font-variant-ligatures: no-common-ligatures; color: #bb2ca2}span.s3 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures; color: #000000}span.s4 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures}span.s5 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s6 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s7 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s8 {font-variant-ligatures: no-common-ligatures; color: #272ad8}span.s9 {font-variant-ligatures: no-common-ligatures; color: #d12f1b}span.s10 {font-variant-ligatures: no-common-ligatures; color: #008400}span.s11 {font: 11.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures; color: #008400}span.s12 {font: 11.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures}

-(void)creatRectButton
{
    //通过类方法来创建 圆角按钮
    UIButton* btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    
    btn.frame=CGRectMake(100, 100, 100, 40);
    
    //设置按钮文字内容
    [btn setTitle:@"button1" forState:UIControlStateNormal]; //正常状态
    [btn setTitle:@"press button" forState:UIControlStateHighlighted]; //按下状态
    //设置文字颜色
    [btn setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
    [btn setTitleColor:[UIColor blueColor] forState:UIControlStateHighlighted];
    //设置风格颜色
    [btn setTintColor:[UIColor whiteColor]];
    //设置文字大小
    btn.titleLabel.font = [UIFont systemFontOfSize:12];
    
    //设置按钮背景颜色
    btn.backgroundColor=[UIColor grayColor];
    
    //按钮事件
    
    //向按钮添加事件函数 UIControlEvent--事件处理函数类型  TouchUpInside--按钮弹起 并光标离开位置在按钮范围内
    [btn addTarget:self action:@selector(pressBtn) forControlEvents:UIControlEventTouchUpInside];
    
    btn.tag=101; //设置按钮标记值 除指针外也可以通过tag区分
    
    
    
    //添加到视图中并显示
    [self.view addSubview:btn];
    
}

-(void)pressBtn{
    NSLog(@"@button pressed");
}

运行效果：

屏幕快照 2016-11-02 下午9.58.02.png

还可以创建一个图片按钮：

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'Heiti SC Light'; color: #008400}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #3d1d81}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; min-height: 13.0px}span.s1 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures}span.s2 {font-variant-ligatures: no-common-ligatures}span.s3 {font-variant-ligatures: no-common-ligatures; color: #bb2ca2}span.s4 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures; color: #000000}span.s5 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s6 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s7 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s8 {font-variant-ligatures: no-common-ligatures; color: #272ad8}span.s9 {font-variant-ligatures: no-common-ligatures; color: #d12f1b}

//可以显示图片的按钮
-(void)createImgBtn{
    //创建一个自定义类型
    UIButton* btnImage=[UIButton buttonWithType:UIButtonTypeCustom];
    btnImage.frame=CGRectMake(100, 300, 50, 50);
    UIImage* icon01=[UIImage imageNamed:@"1.jpeg"];
    UIImage* icon02=[UIImage imageNamed:@"2.jpeg"];
    [btnImage setImage:icon01 forState:UIControlStateNormal];
    [btnImage setImage:icon02 forState:UIControlStateHighlighted];
    
    [self.view addSubview:btnImage];
}

UIWindow

UIWindow是一种特殊的UIView，通常在一个app中只会有一个UIWindow。
iOS程序启动完毕后，创建的第一个视图控件就是UIWindow，接着创建控制器的view，最后将控制器的view添加到UIWindow上，于是控制器的view就显示在屏幕上了。
一个iOS程序之所以能显示到屏幕上，完全是因为它有UIWindow。也就说，没有UIWindow，就看不见任何UI界面。

通过自编程序了解UIWindow创建过程：
在AppDelegate.m文件中修改：

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; min-height: 13.0px}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'Heiti SC Light'; color: #008400}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #008400}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #3d1d81}p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #703daa}p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #bb2ca2}span.s1 {font-variant-ligatures: no-common-ligatures}span.s2 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures}span.s3 {font-variant-ligatures: no-common-ligatures; color: #bb2ca2}span.s4 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s5 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s6 {font: 11.0px 'Heiti SC Light'; font-variant-ligatures: no-common-ligatures}span.s7 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures; color: #000000}span.s8 {font-variant-ligatures: no-common-ligatures; color: #4f8187}span.s9 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s10 {font-variant-ligatures: no-common-ligatures; color: #272ad8}span.s11 {font-variant-ligatures: no-common-ligatures; color: #d12f1b}

//当程序框架初始化成功后，调用此函数
//用来初始化整个程序框架结构。即整个程序对IOS开发工程师的入口函数
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    //创建一个window对象
    //整个程序中只有一个UIWindow对象
    //在程序基本上表示屏幕窗口
    //UIWindow也是继承自UIView，是一个特殊的UIView
    //UIScreen表示屏幕硬件表示类，mainSreen获得主屏幕设备信息
    self.window = [[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];
    //创建一个视图控制器，作为UIWindow的跟视图控制器
    self.window.rootViewController=[[UIViewController alloc]init];
    self.window.backgroundColor=[UIColor blueColor];
    
    UIView* view=[[UIView alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
    view.backgroundColor=[UIColor redColor];
    
    UIView* backView=[[UIView alloc]initWithFrame:CGRectMake(0, 50, 240, 360)];
    backView.backgroundColor = [UIColor greenColor];
    //背景视图
    [backView addSubview:view];
    
    //将backView作为view的父视图.子视图的坐标的参考系是父视图的坐标
    [self.window addSubview:backView];
    

    
    //使window有效并显示到屏幕上
    [self.window makeKeyAndVisible];
    
    //这些window是同一个window
    //当子视图添加到父视图上时，子视图window会被父视图window赋值，打印输出的是window地址
    NSLog(@"%@",view.window);
    NSLog(@"%@",backView.window);
    NSLog(@"%@",self.window);

    return YES;
}