UIscrollView网络加载滚动新闻

　　这个程序是从网上下载的，我稍作了修改。用到了GCD数据加载，因为本人对block不熟，所以看起来十分纠结。等以后笨猪对block的理解更深入了，再做总结。

　　基本功能是从网络下载图片，显示在UIScrollView上，每隔6秒滚动一次，我在源程序基础上做了改动，如果图片还没有加载完成，则显示很酷的风火轮，加载完成风火轮消失。

效果图如下：

这次用到了IB，不过很简单，拖两个控件（UIScrollView和UIPageControl）到View上，再在ViewController.h中声明这两个类型的变量，连起来。如图：

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController{

    IBOutlet UIScrollView *scrollview;
    IBOutlet UIPageControl *page;
    NSArray *Arr;
    int TimeNum;
    BOOL Tend;
}
-(void)AdImg:(NSArray*)arr;
- (void) setCurrentPage:(NSInteger)secondPage;
- (void)createActivityView:(UIImageView*)img;
- (void)stopActivityView:(UIImageView*)img;
@property(retain,nonatomic)UIScrollView *scrollview;
@property(retain,nonatomic)UIPageControl *page;
@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
@synthesize scrollview,page;

- (void)viewDidLoad
{
    [super viewDidLoad];
    [NSTimer scheduledTimerWithTimeInterval:1 target: self selector: @selector(handleTimer:)  userInfo:nil  repeats: YES];
    Arr=[[NSArray alloc]initWithObjects:
                  @"http://www.sootuu.com/photo/uploadfile/2006-4/20064223635877.jpg",
                  @"http://www.sootuu.com/photo/uploadfile/2006-4/2006422377122.jpg",
                  @"http://pic7.nipic.com/20100604/668573_235438084702_2.jpg",nil];
    [self AdImg:Arr];
    [self setCurrentPage:page.currentPage];
    
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
#pragma mark - 6秒换图片
- (void) handleTimer: (NSTimer *) timer
{
    if (TimeNum % 6 == 0 ) {
        if (!Tend) {
            page.currentPage++;
            if (page.currentPage==page.numberOfPages-1) {
                Tend=YES;
            }
        }else{
            page.currentPage--;
            if (page.currentPage==0) {
                Tend=NO;
            }
        }
        [UIView animateWithDuration:1.0 //速度1.0秒
                         animations:^{//修改坐标
                             self.scrollview.contentOffset = CGPointMake(page.currentPage*320,0);
                         }];        
    }
    TimeNum ++;
    NSLog(@"TimeNum==%d",TimeNum);
}
#pragma mark - 下载图片
void UIImageFromURL( NSURL * URL, void (^imageBlock)(UIImage * image), void (^errorBlock)(void) )//block是一段可以在任何时候执行的代码段
{
//这里把imageBlock当做了一个变量，它封装了一段代码，这段代码在-(void)AdImg:(NSArray*)arr中
    dispatch_async( dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0 ), ^(void)
                   {
                       NSData * data = [[NSData alloc] initWithContentsOfURL:URL] ;
                       UIImage * image = [[UIImage alloc] initWithData:data];
                       dispatch_async( dispatch_get_main_queue(), ^(void){//异步加载图
                           if( image != nil )
                           {
                               imageBlock( image );
                           } else {
                               errorBlock();
                           }
                       });
                   });
}

-(void)AdImg:(NSArray*)arr{
    [self.scrollview setContentSize:CGSizeMake(320*[arr count], 211)];
    page.numberOfPages=[arr count];
    for ( int i=0; i<[arr count]; i++) {
        NSString *url=[arr objectAtIndex:i];
        UIImageView *img=[[UIImageView alloc]initWithFrame:CGRectMake(320*i, 0, 320, 211)];
        img.backgroundColor = [UIColor whiteColor];
//        img.tag = 1000 + i;
        [self createActivityView:img];
        [self.scrollview addSubview:img];
        UIImageFromURL([NSURL URLWithString:url], ^( UIImage * image ){
            [img setImage:image];
            [self stopActivityView:img];
                       }, ^(void){});
        [img release];//红色的字体就是上一个函数imageBlock封装起来的代码段，执行的时候直接用这段代码替换void (^imageBlock)(UIImage * image)
    }
}


#pragma mark - scrollView && page
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
    
    page.currentPage=scrollView.contentOffset.x/320;//设置当前页的偏移位置
    [self setCurrentPage:page.currentPage];
    
}
- (void) setCurrentPage:(NSInteger)secondPage {
    
    for (NSUInteger subviewIndex = 0; subviewIndex < [page.subviews count]; subviewIndex++) {//从UIPageControl的subviews中获得每张图片，再替换
        UIImageView* subview = [page.subviews objectAtIndex:subviewIndex];
        CGSize size;
        size.height = 24/2;
     
        size.width = 24/2;
        [subview setFrame:CGRectMake(subview.frame.origin.x, subview.frame.origin.y,
                                     size.width,size.height)];
        if (subviewIndex == secondPage) [subview setImage:[UIImage imageNamed:@"a.png"]];
        else [subview setImage:[UIImage imageNamed:@"d.png"]];//这里是把UIPageControl的小图标换了
    }
    
}

- (void)createActivityView:(UIImageView*)img//创建风火轮
{
    static int size = 40;
    UIActivityIndicatorView *activityView = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    activityView.frame = CGRectMake(img.frame.size.width/2 - size/2, img.frame.size.height/2 - size/2, size, size);
//    activityView.tag = img.tag;
    [img addSubview:activityView];
    [activityView startAnimating];
    [activityView release];
}

- (void)stopActivityView:(UIImageView*)img;//移除风火轮
{
//    UIActivityIndicatorView *actvityIdcator = [[UIActivityIndicatorView alloc]init];
//    actvityIdcator.tag = img.tag;
//    NSLog(@"第%d个加载完成",actvityIdcator.tag);
    if (img.image != nil)
    for (UIView *view in [img subviews]) {//读出UIButton里的所有控件，再选择UIActivityIndicatorView进行更改
        if ([view isKindOfClass:[UIActivityIndicatorView class]]) {
            [view removeFromSuperview];//把风火轮UIActivityIndicatorView移除
        }
    }
}

- (void)dealloc {
    [scrollview release];
    [page release];
    [Arr release];
    [super dealloc];
}

@end