我懒惰地将标志图像加载到具有 16 个国家/地区的 tableview 上。这是我的代码：
#import "ViewController.h"
@implementation ViewController
@synthesize tableView;
@synthesize countryNamesArray;
@synthesize receivedData;
@synthesize flagImage;
@synthesize flagImagesArray;
@synthesize requestsAlreadyMade;
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
#pragma mark - View lifecycle
-(void)issueRequest:(NSString *)fullCountryImageURL{
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:fullCountryImageURL]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// create the connection with the request
// and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData to hold the received data.
// receivedData is an instance variable declared elsewhere.
receivedData = [NSMutableData data];
}
else {
// Inform the user that the connection failed.
}
}
- (void)viewDidLoad
{
requestsAlreadyMade = [[NSMutableArray alloc]init];
flagImagesArray = [[NSMutableArray alloc]init];
for(int x=0; x<16; x++){
[flagImagesArray insertObject:[UIImage imageNamed: @"jollyroger_poisonflag.jpg"] atIndex:x];
}
countryNamesArray=[[NSArray alloc] initWithObjects:@"India",@"USA",@"Antarctica",@"Brazil",@"Canada",@"China",@"France",@"Germany",@"Italy",@"Japan",@"Kenya",@"Malaysia",@"Mexico",@"South Africa",@"United Kingdom",@"Vietnam",nil];
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
}
- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
} else {
return YES;
}
}
-(NSInteger)tableView:(UITableView *)tableview numberOfRowsInSection:(NSInteger)section{
return 16;
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
// This method is called when the server has determined that it
// has enough information to create the NSURLResponse.
// It can be called multiple times, for example in the case of a
// redirect, so each time we reset the data.
// receivedData is an instance variable declared elsewhere.
[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// Append the new data to receivedData.
// receivedData is an instance variable declared elsewhere.
[receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connectiondidFailWithError:(NSError *)error
{
// release the connection, and the data object
// receivedData is declared as a method instance elsewhere
// inform the user
NSLog(@"Connection failed! Error - %@ %@",
[error localizedDescription],
[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
// do something with the data
// receivedData is declared as a method instance elsewhere
NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]);
flagImage = [UIImage imageWithData: receivedData];
if([receivedData length]==19935){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==0)
[flagImagesArray replaceObjectAtIndex:0 withObject:flagImage];
}
}
else if([receivedData length]==9280){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==1)
[flagImagesArray replaceObjectAtIndex:1 withObject:flagImage];
}
}
else if([receivedData length]==9567){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==2)
[flagImagesArray replaceObjectAtIndex:2 withObject:flagImage];
}
}
else if([receivedData length]==12152){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==3)
[flagImagesArray replaceObjectAtIndex:3 withObject:flagImage];
}
}
else if([receivedData length]==10903){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==4)
[flagImagesArray replaceObjectAtIndex:4 withObject:flagImage];
}
}
else if([receivedData length]==11298){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==5)
[flagImagesArray replaceObjectAtIndex:5 withObject:flagImage];
}
}
else if([receivedData length]==8682){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==6)
[flagImagesArray replaceObjectAtIndex:6 withObject:flagImage];
}
}
else if([receivedData length]==6865){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==7)
[flagImagesArray replaceObjectAtIndex:7 withObject:flagImage];
}
}
else if([receivedData length]==10567){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==8)
[flagImagesArray replaceObjectAtIndex:8 withObject:flagImage];
}
}
else if([receivedData length]==9423){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==9)
[flagImagesArray replaceObjectAtIndex:9 withObject:flagImage];
}
}
else if([receivedData length]==8962){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==10)
[flagImagesArray replaceObjectAtIndex:10 withObject:flagImage];
}
}
else if([receivedData length]==12238){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==11)
[flagImagesArray replaceObjectAtIndex:11 withObject:flagImage];
}
}
else if([receivedData length]==5980){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==12)
[flagImagesArray replaceObjectAtIndex:12 withObject:flagImage];
}
}
else if([receivedData length]==10562){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==13)
[flagImagesArray replaceObjectAtIndex:13 withObject:flagImage];
}
}
else if([receivedData length]==9690){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==14)
[flagImagesArray replaceObjectAtIndex:14 withObject:flagImage];
}
}
else if([receivedData length]==11590){
for (NSIndexPath *indexPath in [tableView indexPathsForVisibleRows]){
if(indexPath.row==15)
[flagImagesArray replaceObjectAtIndex:15 withObject:flagImage];
}
}
[tableView reloadData];
}
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
static NSString *cellIdentifier = @"countryCell";
static int numberOfRequests=0;
UITableViewCell *cell=(UITableViewCell *) [self.tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell==nil){
cell=[[UITableViewCell alloc] initWithStyle: UITableViewCellStyleSubtitle reuseIdentifier:cellIdentifier];
}
// Create the request.
NSString *flagImageURLPartOne = @"http://www.imageslink/";
NSString *countryNumber = [NSString stringWithFormat:@"%i", indexPath.row+1];
NSString *flagImageURLPartTwo = @".png";
NSString *fullCountryImageURL = [NSString stringWithFormat:@"%@%@%@", flagImageURLPartOne, countryNumber, flagImageURLPartTwo];
if(!([requestsAlreadyMade containsObject:fullCountryImageURL])){
[self issueRequest:fullCountryImageURL];
[requestsAlreadyMade addObject:fullCountryImageURL];
}
cell.imageView.image=[flagImagesArray objectAtIndex:indexPath.row];
cell.textLabel.text= [countryNamesArray objectAtIndex:indexPath.row];
return cell;
}
-(void) tableView:(UITableView *) tableview didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
}
@end
所以我遇到的问题有点奇怪。当 tableview 首次加载时，初始可见行加载得很好。如果我快速向下滚动到列表的后半部分，所有其他图像延迟加载也很好。但是，如果我非常缓慢地向下滚动，即使在我停止滚动之后，我的国家的一张图片也永远不会加载。有没有人有任何想法可能导致这种情况？