我想创建一个类似Paging with UIScrollView in the tutorial的scrollView。唯一不同的是在我的应用程序中我将.xib文件添加到UIscrollView而不是UIImageView，我从后端部分获取数据而不是静态设置它们。
我发现需要时间的线（它实际上将图像加载到另一个scrollView）：
[self.offerView loadVisiblePages];
这就是那里发生的事情：
@implementation OfferUIView
- (void)initialization {
NSInteger pageCount = self.pageImages.count;
// Set up the array to hold the views for each page
self.pageViews = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < pageCount; ++i) {
[self.pageViews addObject:[NSNull null]];
}
CGSize pagesScrollViewSize = self.scrollView.frame.size;
self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * 3, pagesScrollViewSize.height);
}
- (void)loadVisiblePages {
[self initialization];
// First, determine which page is currently visible
CGFloat pageWidth = self.scrollView.frame.size.width;
NSInteger page = (NSInteger)floor((self.scrollView.contentOffset.x * 2.0f + pageWidth) / (pageWidth * 2.0f));
// Work out which pages we want to load
NSInteger firstPage = page - 1;
NSInteger lastPage = page + 1;
// Purge anything before the first page
for (NSInteger i=0; i<firstPage; i++) {
[self purgePage:i];
}
for (NSInteger i=firstPage; i<=lastPage; i++) {
[self loadPage:i];
}
for (NSInteger i=lastPage+1; i<self.pageImages.count; i++) {
[self purgePage:i];
}
}
我的问题是，当我第一次运行应用程序时，加载图像速度太慢。你能救我吗？
这是.h文件：
@interface ViewController2 : UIViewController {
@private
UIScrollView *scrollView;
}
@property (nonatomic, strong) IBOutlet UIScrollView *scrollView;
@property (nonatomic, strong) PFLogInViewController *login;
@end
.m文件：
@interface ViewController2 ()
@property (nonatomic, strong) NSMutableDictionary *pageImages;
@property (nonatomic, strong) NSMutableArray *companies;
@property (nonatomic, strong) NSMutableArray *offers;
@property (nonatomic, strong) NSMutableArray *pageViews;
@property (nonatomic, strong) OfferUIView *offerView;
@property (nonatomic, assign) NSString *address;
- (void)loadVisiblePages;
- (void)loadPage:(NSInteger)page;
- (void)purgePage:(NSInteger)page;
@end
@implementation ViewController2
@synthesize scrollView = _scrollView;
@synthesize offerView = _offerView;
@synthesize pageImages = _pageImages;
@synthesize companies = _companies;
@synthesize offers = _offers;
@synthesize pageViews = _pageViews;
- (void)loadVisiblePages {
// First, determine which page is currently visible
CGFloat pageWidth = self.scrollView.frame.size.height;
NSInteger page = (NSInteger)floor((self.scrollView.contentOffset.y * 2.0f + pageWidth) / (pageWidth * 2.0f));
// Work out which pages we want to load
NSInteger firstPage = page - 1;
NSInteger lastPage = page + 1;
// Purge anything before the first page
for (NSInteger i=0; i<firstPage; i++) {
[self purgePage:i];
}
for (NSInteger i=firstPage; i<=lastPage; i++) {
[self loadPage:i];
}
for (NSInteger i=lastPage+1; i<self.pageImages.count; i++) {
[self purgePage:i];
}
}
- (void)loadPage:(NSInteger)page {
if (page < 0 || page >= self.pageImages.count) {
// If it's outside the range of what we have to display, then do nothing
return;
}
// Load an individual page, first seeing if we've already loaded it
UIView *pageView = [self.pageViews objectAtIndex:page];
if ((NSNull*)pageView == [NSNull null]) {
CGRect frame = self.scrollView.bounds;
frame.origin.x = 0.0f;
frame.origin.y = frame.size.height * page;
NSArray *views = [[NSBundle mainBundle] loadNibNamed:@"OfferView" owner:self options:nil];
self.offerView = [views objectAtIndex:0];
self.offerView.contentMode = UIViewContentModeScaleAspectFit;
self.offerView.frame = frame;
[self.scrollView addSubview:self.offerView];
[self.pageViews replaceObjectAtIndex:page withObject:self.offerView];
self.offerView.pageId = 1;
Company *company = [self.companies objectAtIndex:page];
self.offerView.labelCompany.text = company.name;
self.offerView.companyAddress = company.address;
Offer *offer = [self.offers objectAtIndex:page];
NSMutableArray *imageArray = [self.pageImages objectForKey:offer.objectId];
self.offerView.pageImages = imageArray;
self.offerView.offerId = offer.objectId;
[self.offerView loadVisiblePages];
self.offerView.labelOffer.text = @"Vid köp för minst";
self.offerView.labelOffer.text =[[self.offerView.labelOffer.text stringByAppendingFormat:@" %i", offer.offer] stringByAppendingString:@"kr."];
[self.offerView.labelDiscount setText: [[NSString stringWithFormat:@"%i", offer.discount] stringByAppendingString:@":-"]];
double deadline = [offer.deadline timeIntervalSinceNow];
double createdAt = [offer.createdAt timeIntervalSinceNow];
double difference = deadline - createdAt;
NSNumber *theDouble = [NSNumber numberWithDouble:difference];
int inputSeconds = [theDouble intValue];
int hours = inputSeconds / 3600;
int minutes = ( inputSeconds - hours * 3600 ) / 60;
//int seconds = inputSeconds - hours * 3600 - minutes * 60;
NSString *theTime = [NSString stringWithFormat:@"%dh %dm", hours, minutes];
[self.offerView.labelDeadline setText:theTime];
}
}
- (void)purgePage:(NSInteger)page {
if (page < 0 || page >= self.pageImages.count) {
// If it's outside the range of what we have to display, then do nothing
return;
}
// Remove a page from the scroll view and reset the container array
UIView *pageView = [self.pageViews objectAtIndex:page];
if ((NSNull*)pageView != [NSNull null]) {
[pageView removeFromSuperview];
[self.pageViews replaceObjectAtIndex:page withObject:[NSNull null]];
}
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
// Set up the image we want to scroll and add it to the scroll view
[self loadDataFromParse];
NSInteger pageCount = self.pageImages.count;
// Set up the array to hold the views for each page
self.pageViews = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < pageCount; ++i) {
[self.pageViews addObject:[NSNull null]];
}
printf("%s\n", [@"ViewDidLoad" UTF8String]);
}
- (void)loadDataFromParse {
self.pageImages = [[NSMutableDictionary alloc] init];
self.companies = [[NSMutableArray alloc] init];
self.offers = [[NSMutableArray alloc] init];
PFQuery *companyQuery = [PFQuery queryWithClassName:@"Company"];
NSArray *companyArray = [companyQuery findObjects];
NSArray *offerArray;
PFQuery *offerQuery = [PFQuery queryWithClassName:@"Offer"];
NSArray *imageArray;
PFQuery *imageQuery = [PFQuery queryWithClassName:@"Image"];
for (NSInteger i=0; i<companyArray.count; i++) {
PFObject *fetchedCompany = [companyArray objectAtIndex:i];
Company *company = [[Company alloc] init];
company.name = [fetchedCompany objectForKey:@"name"];
company.address = [fetchedCompany objectForKey:@"address"];
[offerQuery whereKey:@"company" equalTo:fetchedCompany];
offerArray = [offerQuery findObjects];
for (NSInteger j=0; j<offerArray.count; j++) {
PFObject *fetchedOffer = [offerArray objectAtIndex:j];
Offer *offer = [[Offer alloc] init];
offer.objectId = [fetchedOffer valueForKey:@"objectId"];
offer.offer = [[fetchedOffer objectForKey:@"offer"]integerValue];
offer.discount = [[fetchedOffer objectForKey:@"discount"]integerValue];
offer.deadline = [fetchedOffer objectForKey:@"deadline"];
offer.createdAt = [fetchedOffer objectForKey:@"createdAt"];
[imageQuery whereKey:@"offer" equalTo:fetchedOffer];
imageArray = [imageQuery findObjects];
NSMutableArray *array = [[NSMutableArray alloc] init];
for (NSInteger k=0; k<imageArray.count; k++) {
PFObject *fetchedimage = [imageArray objectAtIndex:k];
[array addObject:fetchedimage];
}
[self.pageImages setObject:array forKey:offer.objectId];
[self.offers addObject:offer];
[self.companies addObject:company];
}
}
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// Set up the content size of the scroll view
CGSize pagesScrollViewSize = self.scrollView.frame.size;
//self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * self.pageImages.count, pagesScrollViewSize.height);
self.scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width, pagesScrollViewSize.height * self.pageImages.count);
// Load the initial set of pages that are on screen
[self loadVisiblePages];
printf("%s\n", [@"ViewWillAppear" UTF8String]);
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
self.offers = nil;
self.companies = nil;
self.pageImages = nil;
self.pageViews = nil;
self.scrollView = nil;
self.offerView = nil;
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
#pragma mark - UIScrollViewDelegate
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
// Load the pages which are now on screen
[self loadVisiblePages];
}
答案 0 :(得分：0)
下载SMPageControl示例..，它可能对你有帮助..
答案 1 :(得分：0)
在加载某些数据的情况下需要花费太多时间，您应该将工作卸载到后台线程。您尝试使用GCD吗？
例如，你会这样做：
dispatch_queue_t preloadQueue = dispatch_queue_create("preload queue", nil);
dispatch_async(preloadQueue, ^{
// do the heavy task here
dispatch_async(dispatch_get_main_queue(), ^{
// set-up all the ui components that are required to be set on the main thread
});
});
同时使用Instruments与Time Profiling Tool一起确定哪条指令需要一段时间。
答案 2 :(得分：0)
为了提高您的响应能力，我建议：
加载UIImageViews并加载UIImages以下方法，以避免iOS缓存图片（在内存中进行手动缓存）：
+ (UIImage *)imageWithContentsOfFile:(NSString *)path
如果加载缩略图是不可接受的，而且您的图片非常大，我会将它们平铺。
您需要检查WWDC 2010中的Designing apps with Scrollviews（需要登录）以及Apple的以下示例：PhotoScroller＆amp; ScrollViewSuite。还有一个来自WWDC 2009的有趣视频，名为掌握iPhone中的滚动视图，其中包括以UITableView单元回收方式回收图像，但我找不到它。