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我想建立一個列車到達時間參考應用程序，它允許我選擇不同的站點並顯示從A到B的時間以及從B到A的時間。所以我使用Apple的Page Control，因爲我想爲每個電臺配備多個頁面，並且每個頁面都會列出所有列車時間。這裏是我的appdelegate：UITableView與自定義單元格一次只加載一行數據
#import "AppDelegate.h"
#import "MyViewController.h"
static NSUInteger kNumberOfPages = 2;
@interface AppDelegate (PrivateMethods)
- (void)loadScrollViewWithPage:(int)page;
- (void)scrollViewDidScroll:(UIScrollView *)sender;
@end
@implementation AppDelegate
@synthesize window, scrollView, pageControl, viewControllers;
- (void)dealloc {
[viewControllers release];
[scrollView release];
[pageControl release];
[window release];
[super dealloc];
}
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// view controllers are created lazily
// in the meantime, load the array with placeholders which will be replaced on demand
NSMutableArray *controllers = [[NSMutableArray alloc] init];
for (unsigned i = 0; i < kNumberOfPages; i++) {
[controllers addObject:[NSNull null]];
}
self.viewControllers = controllers;
[controllers release];
// a page is the width of the scroll view
scrollView.pagingEnabled = YES;
scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * kNumberOfPages, scrollView.frame.size.height);
scrollView.showsHorizontalScrollIndicator = NO;
scrollView.showsVerticalScrollIndicator = NO;
scrollView.scrollsToTop = NO;
scrollView.delegate = self;
pageControl.numberOfPages = kNumberOfPages;
pageControl.currentPage = 0;
// pages are created on demand
// load the visible page
// load the page on either side to avoid flashes when the user starts scrolling
[self loadScrollViewWithPage:0];
[self loadScrollViewWithPage:1];
}
- (void)loadScrollViewWithPage:(int)page {
if (page < 0) return;
if (page >= kNumberOfPages) return;
// replace the placeholder if necessary
MyViewController *controller = [viewControllers objectAtIndex:page];
if ((NSNull *)controller == [NSNull null]) {
controller = [[MyViewController alloc] initWithPageNumber:page];
[viewControllers replaceObjectAtIndex:page withObject:controller];
[controller release];
}
// add the controller's view to the scroll view
if (nil == controller.view.superview) {
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
controller.view.frame = frame;
[scrollView addSubview:controller.view];
}
}
- (void)scrollViewDidScroll:(UIScrollView *)sender {
// We don't want a "feedback loop" between the UIPageControl and the scroll delegate in
// which a scroll event generated from the user hitting the page control triggers updates from
// the delegate method. We use a boolean to disable the delegate logic when the page control is used.
if (pageControlUsed) {
// do nothing - the scroll was initiated from the page control, not the user dragging
return;
}
// Switch the indicator when more than 50% of the previous/next page is visible
CGFloat pageWidth = scrollView.frame.size.width;
int page = floor((scrollView.contentOffset.x - pageWidth/2)/pageWidth) + 1;
pageControl.currentPage = page;
// load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
[self loadScrollViewWithPage:page - 1];
[self loadScrollViewWithPage:page];
[self loadScrollViewWithPage:page + 1];
// A possible optimization would be to unload the views+controllers which are no longer visible
}
// At the begin of scroll dragging, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
pageControlUsed = NO;
}
// At the end of scroll animation, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
pageControlUsed = NO;
}
- (IBAction)changePage:(id)sender {
int page = pageControl.currentPage;
// load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling)
[self loadScrollViewWithPage:page - 1];
[self loadScrollViewWithPage:page];
[self loadScrollViewWithPage:page + 1];
// update the scroll view to the appropriate page
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
[scrollView scrollRectToVisible:frame animated:YES];
// Set the boolean used when scrolls originate from the UIPageControl. See scrollViewDidScroll: above.
pageControlUsed = YES;
}
@end
應用程序委託加載「MyViewController」。我想用我的視圖控制器做什麼，有兩個單獨的普通表，包含不同的信息集。我能夠實現這一點。
然後，我修改了兩個表格，讓自定義單元格包含兩個我希望能夠設置的標籤。這裏是MyViewControler：
#import "MyViewController.h"
#import "CustomCell.h"
static NSArray *__pageControlColorList = nil;
static NSArray *__stationNameList = nil;
@implementation MyViewController
@synthesize stationName;
@synthesize homeBound;
@synthesize workBound;
@synthesize homeBoundTimes;
@synthesize workBoundTimes;
@synthesize Custom;
// Creates the color list the first time this method is invoked. Returns one color object from the list.
+ (UIColor *)pageControlColorWithIndex:(NSUInteger)index {
if (__pageControlColorList == nil) {
__pageControlColorList = [[NSArray alloc] initWithObjects:[UIColor colorWithRed:16.0/255 green:102.0/255 blue:73.0/255 alpha:1.0],
[UIColor colorWithRed:248.0/255 green:155.0/255 blue:70.0/255 alpha:1.0], nil];
}
// Mod the index by the list length to ensure access remains in bounds.
return [__pageControlColorList objectAtIndex:index % [__pageControlColorList count]];
}
//Creates the station list the first time this method is invoked. Returns one string object from the list.
+ (NSString *)pageControlStationWithIndex:(NSUInteger)index {
if (__stationNameList == nil) {
__stationNameList = [[NSArray alloc] initWithObjects:[NSString stringWithFormat:@"Bramalea"], [NSString stringWithFormat:@"Erindale"], nil];
}
//Mod the index by the list length to ensure access remains in bounds.
return [__stationNameList objectAtIndex:index % [__stationNameList count]];
}
//Creates the station list the first time this method is invoked. Returns one string object from the list.
+ (NSArray *)HomeTimesByIndex:(NSUInteger)index {
if (index == 0) {
return [[NSArray alloc] initWithObjects:@"5:55 am", @"6:49 am", @"7:14 am", @"7:30 am", @"7:38 am",
@"8:07 am", @"9:20 am", @"10:25 am", @"11:06 am", @"12:15 pm",
@"1:45 pm", @"2:51 pm", @"3:51 pm", @"4:51 pm", @"5:51 pm",
@"6:51 pm", @"7:21 pm", @"7:51 pm", @"8:51 pm", @"9:51 pm", nil];
} else {
return [[NSArray alloc] initWithObjects:@"5:10 am", @"5:45 am", @"6:45 am", @"7:10 am",
@"7:30 am", @"7:45 am", @"8:00 am", @"8:15 am",
@"8:30 am", @"9:05 am", @"9:40 am", @"10:15 am",
@"10:45 am", @"11:15 am", @"11:45 am", @"12:15 pm",
@"12:45 pm", @"1:15 pm", @"1:45 pm", @"2:15 pm", @"2:45 pm",
@"3:15 pm", @"3:45 pm", @"4:15 pm", @"5:20 pm", @"6:20 pm",
@"7:15 pm", @"8:15 pm", @"9:15 pm", @"10:15 pm", @"11:15 pm", nil];
}
}
+ (NSArray *)WorkTimesByIndex:(NSUInteger)index {
if (index == 0) {
return [[NSArray alloc] initWithObjects:@"6:25 am", @"7:30 am", @"8:30 am", @"9:40 am", @"11:30 am", @"1:00 pm", @"1:50 pm",
@"2:00 pm", @"2:45 pm", @"4:15 pm", @"4:45 pm", @"5:15 pm", @"5:45 pm", @"6:45 pm",
@"7:20 pm", @"7:35 pm", @"7:55 pm", @"8:15 pm", @"8:35 pm", @"9:00 pm", @"9:30 pm",
@"10:00 pm", @"10:30 pm", @"11:00 pm", @"11:30 pm", @"12:01 am", @"12:30 am", @"1:30 am", nil];
} else {
return [[NSArray alloc] initWithObjects:
@"6:20 am", @"7:20 am", @"8:20 am", @"9:20 am", @"10:20 am", @"11:20 am", @"12:20 pm",
@"12:50 pm", @"1:20 pm", @"1:40 pm", @"2:00 pm", @"2:20 pm", @"2:40 pm", @"2:55 pm",
@"3:10 pm", @"3:25 pm", @"4:30 pm", @"4:50 pm", @"5:10 pm", @"5:25 pm", @"5:40 pm",
@"6:10 pm", @"7:00 pm", @"7:25 pm", @"7:40 pm", @"7:55 pm", @"8:10 pm", @"8:30 pm",
@"8:50 pm", @"9:10 pm", @"9:30 pm", @"9:50 pm", @"10:20 pm", @"11:20 pm", @"12:20 am", @"1:20 am", nil];
}
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
CGRect frame = self.view.frame;
frame.size.height = 600;
self.view.frame = frame;
}
// Load the view nib and initialize the pageNumber ivar.
- (id)initWithPageNumber:(int)page {
if (self = [super initWithNibName:@"Station" bundle:nil]) {
pageNumber = page;
}
return self;
}
- (void)dealloc {
[stationName release];
[homeBound release];
[workBound release];
[homeBoundTimes release];
[workBoundTimes release];
[Custom release];
[super dealloc];
}
// Set the label and background color when the view has finished loading.
- (void)viewDidLoad {
//Get station name and set station texts
stationName.text = [MyViewController pageControlStationWithIndex:pageNumber];
homeBound.text = [NSString stringWithFormat:@"Next Train From Union to %@:", [MyViewController pageControlStationWithIndex:pageNumber]];
workBound.text = [NSString stringWithFormat:@"Next Train From %@ to Union:", [MyViewController pageControlStationWithIndex:pageNumber]];
self.view.backgroundColor = [MyViewController pageControlColorWithIndex:pageNumber];
NSArray *arrayHome = [MyViewController HomeTimesByIndex:pageNumber];
NSArray *arrayWork = [MyViewController WorkTimesByIndex:pageNumber];
self.homeBoundTimes = arrayHome;
self.workBoundTimes = arrayWork;
[arrayHome release];
[arrayWork release];
}
#pragma mark -
#pragma mark Table View Data Source Methods
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
if ([tableView tag] == 0) {
return [self.homeBoundTimes count];
} else if ([tableView tag] == 1) {
return [self.workBoundTimes count];
}
return 0;
}
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *CustomCellIdentifier = @"CustomCellIdentifier";
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:CustomCellIdentifier];
if (cell == nil) {
[[NSBundle mainBundle] loadNibNamed:@"CustomCell" owner:self options:nil];
cell = self.Custom;
}
NSUInteger row = [indexPath row];
if ([tableView tag] == 0) {
cell.arriveTimeLabel.text = [homeBoundTimes objectAtIndex:row];
cell.departTimeLabel.text = [homeBoundTimes objectAtIndex:row];
} else if ([tableView tag] == 1) {
cell.arriveTimeLabel.text = [workBoundTimes objectAtIndex:row];
cell.departTimeLabel.text = [workBoundTimes objectAtIndex:row];
}
return cell;
}
@end
現在加載到表中的值是硬編碼的（接下來試驗db）。
我的問題是，當查看錶時，只有第一行有數據，並且當我開始向下滾動時加載其他數據「sorta」。通過「sorta」，一次只能加載第一行。我只能看到所有數據，當我滾動到底部時，再次向上滾動或選擇一行時。但是這些信息並不總是保持不變。有時當我滾動時，我會丟失信息，直到我再次滾動該特定行。
有沒有人有任何想法，爲什麼發生這種情況？
編輯：吉姆的答案做到了。這裏是我的修飾方法：
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
CustomCell *cell = [tableView dequeueReusableCellWithIdentifier:@"CustomCellIdentifier"];
if (cell == nil) {
// Load the top-level objects from the custom cell XIB.
NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"CustomCell" owner:self options:nil];
// Grab a pointer to the first object (presumably the custom cell, as that's all the XIB should contain).
cell = [topLevelObjects objectAtIndex:0];
NSUInteger row = [indexPath row];
if ([tableView tag] == 0) {
cell.arriveTimeLabel.text = [homeBoundTimes objectAtIndex:row];
cell.departTimeLabel.text = [homeBoundTimes objectAtIndex:row];
} else if ([tableView tag] == 1) {
cell.arriveTimeLabel.text = [workBoundTimes objectAtIndex:row];
cell.departTimeLabel.text = [workBoundTimes objectAtIndex:row];
}
}
return cell;
}