开源中国iOS客户端学习——(二)下拉刷新特效EGOTableViewPullRefresh

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2015.8.19 更新

考虑到还会有很多童鞋会看到该Blog，在此做一个说明，开源中国iOS开源客户端源码已做重构，请下载最新的源码学习（注：本Blog不一定适用与新的代码学习）。

新repo地址：http://git.oschina.net/oschina/iphone-app。

另外，这篇Blog收集了一些其他社区的客户端源码，源码也正在不断更新中，有的也上架appstore。

访问地址：http://duxinfeng.com/2015/07/14/iOS%E5%BC%80%E6%BA%90App%E6%95%B4%E7%90%86/

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打开开源中国iOS客户端应用程序第一步就是加载数据，经常我们在第二次以后打开的时候，我们界面显示的是上一次更新的数据，此时我们想看最新内容就需要去刷新数据加载这些内容，加载需要一个等待过程，如何能让用户在等待过程中不焦急，能够等待这个过程完成，这就需要给用户一个心里安慰，让用户知道该软件正在很努力很努力的执行自己命令，这就需要我们为自己应用程序添加一些特效；

      开源中国iOS客户端用到了不少特效，这些特效在当前很多应用软件中都比较流行，基本上这些特效都属于第三方类库，本次想说的是下拉刷新特效，EGOTableViewPullRefresh最开始是在Twitter中使用，最后做了开源，然后很多应用添加这个特效，常作为加载数据时将等待时间作为一个动画来过渡；

下拉刷新类库EGOTableViewPullRefresh资源文件下载地址：

 https://github.com/enormego/EGOTableViewPullRefresh/tree/

先这个特效的效果图

  

在EGOTableViewPullRefresh资源文件中有两个文件，.m和.h文件，还有资源图片，就是下拉刷新箭头

资源图片一共4种色，可以根据喜好选用不同色的箭头，只需在EGORefreshTableHeaderView.m文件中修改一下。按照大小尺寸又可分两种，较大尺寸是用于iPad上使用的。

针对这些第三方类库，我们没必要去深入研究它们内部实现机制原理，只要知道怎么用就可以。不过，看一看别人实现原理，学学别人的方法还是很不错的，了解下人家牛人程序是怎么写的；

EGORefreshTableHeaderView.h

#import <UIKit/UIKit.h>#import <QuartzCore/QuartzCore.h>typedef enum{EGOOPullRefreshPulling = 0,EGOOPullRefreshNormal,EGOOPullRefreshLoading,} EGOPullRefreshState;@protocol EGORefreshTableHeaderDelegate;@interface EGORefreshTableHeaderView : UIView {id _delegate;EGOPullRefreshState _state;UILabel *_lastUpdatedLabel;UILabel *_statusLabel;CALayer *_arrowImage;UIActivityIndicatorView *_activityView;}@property(nonatomic,assign) id <EGORefreshTableHeaderDelegate> delegate;- (id)initWithFrame:(CGRect)frame arrowImageName:(NSString *)arrow textColor:(UIColor *)textColor;- (void)refreshLastUpdatedDate;- (void)egoRefreshScrollViewDidScroll:(UIScrollView *)scrollView;- (void)egoRefreshScrollViewDidEndDragging:(UIScrollView *)scrollView;- (void)egoRefreshScrollViewDataSourceDidFinishedLoading:(UIScrollView *)scrollView;@end//定义协议方法@protocol EGORefreshTableHeaderDelegate//下拉的时候调用此方法- (void)egoRefreshTableHeaderDidTriggerRefresh:(EGORefreshTableHeaderView*)view;//判断刷新状态情况，正在刷新或者是没刷新- (BOOL)egoRefreshTableHeaderDataSourceIsLoading:(EGORefreshTableHeaderView*)view;@optional//返回刷新时间，回调方法- (NSDate*)egoRefreshTableHeaderDataSourceLastUpdated:(EGORefreshTableHeaderView*)view;@end

首先是定义了一个枚举类型EGOPullRefreshState表示当前我们操作在哪种状态下，有下拉状态、正常状态、数据加载状态；

@protocol EGORefreshTableHeaderDelegate;表示声明有这个协议，该协议里面声明了一些方法，只要其他的类遵循了这个协议（也就是遵循了它的规定），就可以去实现协议里面方法，协议里的方法是留给遵循这个协议的类去实现的，也是留给外部实现接口；

EGORefreshTableHeaderView成员变量定义两个label用于提示下拉过程所处状态，和显示的刷新时间。定义的CALayer类对象装载显示图片。UIActivityIndicatorView类对象显示一个等待动画；

@property(nonatomic,assign)id <EGORefreshTableHeaderDelegate> delegate;声明一个协议对象；

接着下面的是EGORefreshTableHeaderView类成员函数，用于实现类库中下拉刷新的效果；

最后定义了4个协议方法，其中最后一个协议方法为可选实现；

下面是EGORefreshTableHeaderView.m文件，想说的都在注释里

#import "EGORefreshTableHeaderView.h"#define TEXT_COLOR [UIColor colorWithRed:87.0/255.0 green:108.0/255.0 blue:137.0/255.0 alpha:1.0]#define FLIP_ANIMATION_DURATION 0.18f//设置的一个私有接口，只能本类来使用@interface EGORefreshTableHeaderView (Private)- (void)setState:(EGOPullRefreshState)aState;@end@implementation EGORefreshTableHeaderView@synthesize delegate=_delegate;//初始化框架属性，- (id)initWithFrame:(CGRect)frame arrowImageName:(NSString *)arrow textColor:(UIColor *)textColor  {    if((self = [super initWithFrame:frame])) {//self.view自动适应bounds的宽度self.autoresizingMask = UIViewAutoresizingFlexibleWidth;//        self.view背景色和透明度设置self.backgroundColor = [UIColor colorWithRed:226.0/255.0 green:231.0/255.0 blue:237.0/255.0 alpha:1.0];UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0.0f, frame.size.height - 30.0f, self.frame.size.width, 20.0f)];label.autoresizingMask = UIViewAutoresizingFlexibleWidth;label.font = [UIFont systemFontOfSize:12.0f];label.textColor = textColor;//        label文本阴影颜色label.shadowColor = [UIColor colorWithWhite:0.9f alpha:1.0f];label.shadowOffset = CGSizeMake(0.0f, 1.0f);label.backgroundColor = [UIColor clearColor];label.textAlignment = UITextAlignmentCenter;[self addSubview:label];_lastUpdatedLabel=label;[label release];label = [[UILabel alloc] initWithFrame:CGRectMake(0.0f, frame.size.height - 48.0f, self.frame.size.width, 20.0f)];label.autoresizingMask = UIViewAutoresizingFlexibleWidth;label.font = [UIFont boldSystemFontOfSize:13.0f];label.textColor = textColor;label.shadowColor = [UIColor colorWithWhite:0.9f alpha:1.0f];label.shadowOffset = CGSizeMake(0.0f, 1.0f);label.backgroundColor = [UIColor clearColor];label.textAlignment = UITextAlignmentCenter;[self addSubview:label];_statusLabel=label;[label release];CALayer *layer = [CALayer layer];layer.frame = CGRectMake(25.0f, frame.size.height - 65.0f, 30.0f, 55.0f);//        设置layer在view上以某种形式适应layer.contentsGravity = kCAGravityResizeAspect;layer.contents = (id)[UIImage imageNamed:arrow].CGImage;//        判断设备版本，因为一些iOS特性是在最后新增的，要求设备配置高一些，所以做一下判断#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 40000if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {layer.contentsScale = [[UIScreen mainScreen] scale];}#endif[[self layer] addSublayer:layer];_arrowImage=layer;UIActivityIndicatorView *view = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];view.frame = CGRectMake(25.0f, frame.size.height - 38.0f, 20.0f, 20.0f);[self addSubview:view];_activityView = view;[view release];[self setState:EGOOPullRefreshNormal];    }    return self;}

//初始化当前视图的frame- (id)initWithFrame:(CGRect)frame  {  return [self initWithFrame:frame arrowImageName:@"blueArrow.png" textColor:TEXT_COLOR];}#pragma mark -#pragma mark Setters//获取最后一次更新的时间- (void)refreshLastUpdatedDate {if ([_delegate respondsToSelector:@selector(egoRefreshTableHeaderDataSourceLastUpdated:)]) {NSDate *date = [_delegate egoRefreshTableHeaderDataSourceLastUpdated:self];//NSDateFormatter实例创建字符串，来表示NSDate和NSCalendarDate对象，已预订格式化字符串输出  [NSDateFormatter setDefaultFormatterBehavior:NSDateFormatterBehaviorDefault];NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];//        设置日期输出格式[dateFormatter setDateStyle:NSDateFormatterShortStyle];//        设置时间显示格式[dateFormatter setTimeStyle:NSDateFormatterShortStyle];//_lastUpdatedLabel.text = [NSString stringWithFormat:@"Last Updated: %@", [dateFormatter stringFromDate:date]];        _lastUpdatedLabel.text = [NSString stringWithFormat:@"最后更新: %@", [dateFormatter stringFromDate:date]];//        存储_lastUpdatedLabel.text内容，放到字典中[[NSUserDefaults standardUserDefaults] setObject:_lastUpdatedLabel.text forKey:@"EGORefreshTableView_LastRefresh"];//        将NSUserDefaults存储数据放到磁盘[[NSUserDefaults standardUserDefaults] synchronize];} else {_lastUpdatedLabel.text = nil;}}

- (void)setState:(EGOPullRefreshState)aState{switch (aState) {            /*触摸屏幕下拉状态*/case EGOOPullRefreshPulling://_statusLabel.text = NSLocalizedString(@"Release to refresh...", @"Release to refresh status");            _statusLabel.text = @"松开即可刷新";//            设置下拉刷新过程，箭头的图片的一个动画过程[CATransaction begin];//            动画时间[CATransaction setAnimationDuration:FLIP_ANIMATION_DURATION];//            下拉刷新箭头一个翻转过程，(M_PI / 180.0)是角度转换为弧度            _arrowImage.transform = CATransform3DMakeRotation((M_PI / 180.0) * 180.0f, 0.0f, 0.0f, 1.0f);//            动画结束[CATransaction commit];break;            /*刚开始触摸屏幕准备下拉的时候的状态*/case EGOOPullRefreshNormal:if (_state == EGOOPullRefreshPulling) {[CATransaction begin];[CATransaction setAnimationDuration:FLIP_ANIMATION_DURATION];_arrowImage.transform = CATransform3DIdentity;[CATransaction commit];}//_statusLabel.text = NSLocalizedString(@"Pull down to refresh...", @"Pull down to refresh status");            _statusLabel.text = @"下拉可以刷新";[_activityView stopAnimating];[CATransaction begin];//            因为下拉刷新完成好就不需要下拉动画，此时_activityView动画显示//            显示事物关闭动画效果 kCFBooleanTrue关闭 kCFBooleanFalse开启[CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions]; _arrowImage.hidden = NO;_arrowImage.transform = CATransform3DIdentity;[CATransaction commit];//更新下时间[self refreshLastUpdatedDate];break;            /*触摸手指松开，完成下拉操作的状态*/case EGOOPullRefreshLoading://_statusLabel.text = NSLocalizedString(@"Loading...", @"Loading Status");            _statusLabel.text = @"加载中";[_activityView startAnimating];[CATransaction begin];[CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions]; _arrowImage.hidden = YES;[CATransaction commit];break;default:break;}_state = aState;}

#pragma mark -#pragma mark ScrollView Methods- (void)egoRefreshScrollViewDidScroll:(UIScrollView *)scrollView {if (_state == EGOOPullRefreshLoading) {CGFloat offset = MAX(scrollView.contentOffset.y * -1, 0);offset = MIN(offset, 60);scrollView.contentInset = UIEdgeInsetsMake(offset, 0.0f, 0.0f, 0.0f);} else if (scrollView.isDragging) {BOOL _loading = NO;if ([_delegate respondsToSelector:@selector(egoRefreshTableHeaderDataSourceIsLoading:)]) {_loading = [_delegate egoRefreshTableHeaderDataSourceIsLoading:self];}if (_state == EGOOPullRefreshPulling && scrollView.contentOffset.y > -65.0f && scrollView.contentOffset.y < 0.0f && !_loading) {[self setState:EGOOPullRefreshNormal];} else if (_state == EGOOPullRefreshNormal && scrollView.contentOffset.y < -65.0f && !_loading) {[self setState:EGOOPullRefreshPulling];}//设置下拉属性scrollView框架恢复初始位置if (scrollView.contentInset.top != 0) {//        A UIEdgeInsets struct whose top, left, bottom, and right fields are all set to the value 0.scrollView.contentInset = UIEdgeInsetsZero;}}}- (void)egoRefreshScrollViewDidEndDragging:(UIScrollView *)scrollView {BOOL _loading = NO;if ([_delegate respondsToSelector:@selector(egoRefreshTableHeaderDataSourceIsLoading:)]) {_loading = [_delegate egoRefreshTableHeaderDataSourceIsLoading:self];}if (scrollView.contentOffset.y <= - 65.0f && !_loading) {if ([_delegate respondsToSelector:@selector(egoRefreshTableHeaderDidTriggerRefresh:)]) {[_delegate egoRefreshTableHeaderDidTriggerRefresh:self];}[self setState:EGOOPullRefreshLoading];[UIView beginAnimations:nil context:NULL];[UIView setAnimationDuration:0.2];scrollView.contentInset = UIEdgeInsetsMake(60.0f, 0.0f, 0.0f, 0.0f);[UIView commitAnimations];}}//数据加载完成后调用此方法- (void)egoRefreshScrollViewDataSourceDidFinishedLoading:(UIScrollView *)scrollView {[UIView beginAnimations:nil context:NULL];[UIView setAnimationDuration:.3];//    数据加载完成后，scrollView恢复位置大小[scrollView setContentInset:UIEdgeInsetsMake(0.0f, 0.0f, 0.0f, 0.0f)];[UIView commitAnimations];//数据加载完成，[self setState:EGOOPullRefreshNormal];}

#pragma mark -#pragma mark Dealloc- (void)dealloc {_delegate=nil;_activityView = nil;_statusLabel = nil;_arrowImage = nil;_lastUpdatedLabel = nil;    [super dealloc];}@end

当我们想使用这个下拉刷新类库的时候，在使用类里声明这个协议<EGORefreshTableHeaderDelegate>,把当前类self交付给下拉刷新库的协议对象，也就是xx.delegate=self;

怎样让其他类来使用这里面效果，这时我们就可以委托另一个类来实现协议的方法。

选中一个协议方法，右键选择Jump to Definition就可以看到哪些类被委托了，怎样使用了这个类的协议方法：

正在学习过程中，错误之处请指正，欢迎交流，共同学习；

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