设定三原色的值, 生成对应的屏幕背景

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate,UITextFieldDelegate> //添加协议
//编辑环境为MRC, 改用 retain 修饰实例变量
@property (retain, nonatomic) UIWindow *window;

@end

#import "AppDelegate.h"

@interface AppDelegate (){
//用Extension方法扩展实例变量的作用域
UILabel *redLabel;
UILabel *greenLabel;
UILabel *blueLabel;
UITextField *redTextField;
UITextField *greenTextField;
UITextField *blueTextField;

}

@end

@implementation AppDelegate

//编辑环境选用的是MRC模式, 需重写dealloc方法
- (void)dealloc
{
[_window release];
[super dealloc];
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];

//创建redLabel
redLabel = [[UILabel alloc] initWithFrame:CGRectMake(50, 100, 80, 30)];
redLabel.backgroundColor = [UIColor redColor];
NSLog(@"%@",[UIFont familyNames]);
redLabel.font = [UIFont fontWithName:@"Courier New" size:25];
redLabel.textAlignment = NSTextAlignmentCenter;
redLabel.text = @"Red";
redLabel.textColor = [UIColor whiteColor];
[self.window addSubview:redLabel];
[redLabel release];

//创建redTextField
redTextField = [[UITextField alloc] initWithFrame:CGRectMake(160, 100, 165, 30)];
redTextField.tag = 101;
redTextField.backgroundColor = [UIColor whiteColor];
redTextField.placeholder = @"请输入0-255的数";
redTextField.borderStyle = UITextBorderStyleRoundedRect;
[self.window addSubview:redTextField];
[redTextField release];

//创建greenLabel
greenLabel = [[UILabel alloc] initWithFrame:CGRectMake(50, 150, 80, 30)];
greenLabel.backgroundColor = [UIColor greenColor];
greenLabel.text= @"Green";
greenLabel.textColor = [UIColor whiteColor];
greenLabel.font = [UIFont fontWithName:@"Courier New" size:25];
greenLabel.textAlignment = NSTextAlignmentCenter;
[self.window addSubview:greenLabel];
[greenLabel release];

//创建greenTextField
greenTextField = [[UITextField alloc] initWithFrame:CGRectMake(160, 150, 165, 30)];
greenTextField.tag = 102;
greenTextField.backgroundColor = [UIColor whiteColor];
greenTextField.placeholder = @"请输入0-255的数";
greenTextField.borderStyle = UITextBorderStyleRoundedRect;
[self.window addSubview:greenTextField];
[greenTextField release];

//创建blueLabel
blueLabel = [[UILabel alloc] initWithFrame:CGRectMake(50, 200, 80, 30)];
blueLabel.backgroundColor = [UIColor blueColor];
blueLabel.text = @"Blue";
blueLabel.textColor = [UIColor whiteColor];
blueLabel.textAlignment = NSTextAlignmentCenter;
blueLabel.font = [UIFont fontWithName:@"Courier New" size:25];
[self.window addSubview:blueLabel];
[blueLabel release];

//创建blueTextField
blueTextField = [[UITextField alloc] initWithFrame:CGRectMake(160, 200, 165, 30)];
blueTextField.tag = 103;
blueTextField.backgroundColor = [UIColor whiteColor];
blueTextField.placeholder = @"请输入0-255的数";
blueTextField.borderStyle = UITextBorderStyleRoundedRect;
[self.window addSubview:blueTextField];
[blueTextField release];

//创建okButton
UIButton *okButton = [UIButton buttonWithType:UIButtonTypeSystem];
okButton.frame = CGRectMake(150, 280, 75, 30);
okButton.backgroundColor = [UIColor whiteColor];
[okButton setTitle:@"确定" forState:UIControlStateNormal];
[self.window addSubview:okButton];
[okButton addTarget:self action:@selector(submit) forControlEvents:UIControlEventTouchUpInside];

- (void)submit {
CGFloat Red, Green, Blue;
Red = [redTextField.text integerValue] / 255.;
Green = [greenTextField.text integerValue] / 255.;
Blue = [blueTextField.text integerValue] / 255.;

self.window.backgroundColor = [UIColor colorWithRed: Red green:Green  blue:Blue alpha:1.0];
}