iPhone开发多视图技术总结之四：Page Control .

第一次使用某个App时，一般会有欢迎界面，向右滑动屏幕会出现该App的新增功能或功能介绍或使用帮助相关的界面。通过PageControl可以实现该效果。


实现的功能：通过PageControl，实现多视图切换。


关键词：多视图 PageControl UIPageContrller


1、创建一个Empty Application工程，命名为：MultiView-Navigation，如下图

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2、选中工程中的Group MultiView-Tab，然后按住CMD（Windows键）+N，新建视图控制器PageControlViewController，如下图
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3、依照上步操作，新建视图控制器WelcomeViewController、FeatureListViewController





4、万事俱备，开始编写代码，首先修改AppDelegate，AppDelegate.h如下：

#import <UIKit/UIKit.h>
#import "PageControlViewController.h"
#import "WelcomeViewController.h"
@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) PageControlViewController *pageControlViewController;

@end

AppDelegate.m主要修改didFinishLaunchingWithOptions方法，如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.pageControlViewController = [[PageControlViewController alloc]initWithNibName:@"PageControlViewController" bundle:nil];
    //设置rootViewController
    self.window.rootViewController = pageControlViewController;
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

5、视图控制器WelcomeViewController、FeatureListViewController仅仅修改了源代码文件，设置了一下背景色，如下：

@implementation WelcomeViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        self.view.backgroundColor = [UIColor redColor];
    }
    return self;
}

@implementation FeatureListViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        self.view.backgroundColor = [UIColor greenColor];
    }
    return self;
}

6、主要工作在PageControlViewController中，PageControlViewController.h如下：

#import <UIKit/UIKit.h>
#import "WelcomeViewController.h"
#import "FeatureListViewController.h"
@interface PageControlViewController : UIViewController<UIScrollViewDelegate>{
    BOOL pageControlUsed;//用于区分是点击PageControll换页还是通过滚动scrollView换页
}

//添加代码
@property (strong, nonatomic) UIPageControl *pageControl;
@property (strong, nonatomic) UIScrollView *scrollView;
@property (strong, nonatomic) WelcomeViewController *welComeViewController;
@property (strong, nonatomic) FeatureListViewController *featureListViewController;

-(void)pageControlChanged:(id)sender;
@end

PageControlViewController.m如下：

#import "PageControlViewController.h"

@interface PageControlViewController ()

@end

@implementation PageControlViewController
@synthesize pageControl;
@synthesize scrollView;
@synthesize welComeViewController;
@synthesize featureListViewController;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
	CGRect frame = [UIScreen mainScreen].applicationFrame;
    int width = frame.size.width;
    int height = frame.size.height;
  
    frame = CGRectMake(0, 0, width, height);
    //初始化scrollView
    scrollView = [[UIScrollView alloc]initWithFrame:frame];
    scrollView.showsVerticalScrollIndicator = NO;
    scrollView.showsHorizontalScrollIndicator = YES;
    scrollView.pagingEnabled = YES;
    scrollView.contentSize = CGSizeMake(width*2, height);//scrollView内存大小
    scrollView.scrollsToTop = NO;
    //设置代理
    scrollView.delegate = self;
    
    
    int pageControlHeight = 50;
    NSLog(@"width=%d,height=%d",width,height);
    //初始化pageControl
    pageControl = [[UIPageControl alloc]initWithFrame:CGRectMake(0, height-pageControlHeight, width, pageControlHeight)];
    
    //pageControl设定
    pageControl.numberOfPages = 2; //2页
    pageControl.currentPage = 0;
	pageControl.hidesForSinglePage = NO;
	pageControl.backgroundColor = [UIColor blackColor];
    [pageControl addTarget:self action:@selector(pageControlChanged:) forControlEvents:UIControlEventValueChanged];
    
    //初始化welComeViewController、featureListViewController
    welComeViewController = [[WelcomeViewController alloc]initWithNibName:@"WelcomeViewController" bundle:nil];
    featureListViewController = [[FeatureListViewController alloc]initWithNibName:@"FeatureListViewController" bundle:nil];
    
    //设定welComeViewController的位置
    frame = scrollView.frame;
    frame.origin.y = 0;
    welComeViewController.view.frame = frame;
    
    //设定featureListViewController的位置
    frame.origin.x = frame.size.width;
    featureListViewController.view.frame = frame;
    
    //将welComeViewController、featureListViewController加入到scrollView中
    [scrollView addSubview:welComeViewController.view];
    [scrollView addSubview:featureListViewController.view];
    //scrollView设置为黑色背景
    scrollView.backgroundColor = [UIColor blackColor];
    
    [self.view insertSubview:scrollView atIndex:0];
    //将pageControl的atIndex设置为1，pageControl的view在scrollView的view的上层
    [self.view insertSubview:pageControl atIndex:1];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    pageControl = nil;
    scrollView = nil;
    welComeViewController = nil;
    featureListViewController = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

//点击pageControl上的白色点触发的事件
-(void)pageControlChanged:(id)sender{
    int page = pageControl.currentPage;
    NSLog(@"page=%d",page);
    CGRect frame = scrollView.frame;
    frame.origin.x = frame.size.width*page;
    frame.origin.y = 0;
    [scrollView scrollRectToVisible:frame animated:YES];
    pageControlUsed = YES; //用户通过点击Page Control换页时将其设置为YES
}


#pragma pageControl methods
- (void)scrollViewDidScroll:(UIScrollView *)sender{
    NSLog(@"scrollViewDidScroll...");
    if(pageControlUsed){//如果用户通过点击Page Control换页，则不做处理
        return;
    }
    CGFloat pageWidth = scrollView.frame.size.width;
    NSLog(@"pageWidth=%.2f,scrollView.contentOffset.x=%.2f",pageWidth,scrollView.contentOffset.x);
    NSLog(@"@ %.2f,%2.f",floor(-0.5),floor(-0.6));
    //计算滚到哪页
    int page = floor((scrollView.contentOffset.x-pageWidth/2)/pageWidth)+1;
    pageControl.currentPage = page;
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
    pageControlUsed = NO;//滚动结束后将pageControlUsed重置为NO
}


@end

UIPageControl由一系列小圆点组成，每个点代表一页，白色的点代表当前选中的页。


其实现多视图的原理是scrollView的宽度为WelcomeViewController、FeatureListViewController中View的宽度之和，并且WelcomeViewController、FeatureListViewController的View都是作为scrollView的子视图。当第一页被选中时显示WelcomeViewController的view，但是第二页被选中时显示FeatureListViewController的view。



7、编译、运行，效果如下：

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