不使用storyboard(或xib)，代码创建的helloworld程序

本单元教程基于 ”程序员长弓——张燕广“ 的 iphone开发教程，使用最新版的 ios9 和 xcode7 作为开发工具编译运行。链接地址  http://blog.csdn.net/m_changgong/article/details/8029211

初始化及展示UI组件，除了使用storyboard(或xib)还可以纯手工编写Code实现（这点所以GUI语言都是一样的）

1、修改ViewController.m文件，在viewDidLoad中添加

//
//  ViewController.m
//  HelloWorld
//
//  Created by chy龙神 on 5/18/16.
//  Copyright © 2016 555chy. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController


- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    NSLog(@"viewDidLoad");
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
    label.text = @"viewDidLoad hello world";
    [self.view addSubview:label];
    //[label release];
}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

运行结果

2、添加loadView方法

-(void)loadView {
    //[super loadView];
    NSLog(@"loadView");
    //手工初始化view
    //applicationFrame is already deprecated: first deprecated in IOS9.0
    //UIView *view = [[UIView alloc] initWithFrame: [UIScreen mainScreen].applicationFrame];
    UIView *view = [[UIView alloc] initWithFrame: [UIScreen mainScreen].bounds];
    self.view = view;
    UILabel *label2 = [[UILabel alloc] initWithFrame:CGRectMake(0,200,200,200)];
    label2.text = @"loadView hello world";
    [self.view addSubview:label2];
    //'release' is unavaliable: not avaliable in automatic reference counting mode, ARC forbids explict message send of 'release'
    //[label2 release];
}

运行结果

我们发现是全黑的。为什么会是这样的呢？

原因是Label的字体默认是黑色的，背景默认是透明的；而UIView的背景色则默认是黑的，所以导致了全黑的界面。

3、下面我们为UIView上色

UIColor *color = [UIColor colorWithRed:1.0 green:0 blue:0 alpha:1.0];
[view setBackgroundColor: color];

运行结果