ios: laden Sie neue Daten in die UICollectionView

Verwenden, die asynchron abrufen, um Daten vom server und zeigt Sie in der collectionView

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    YourDataModel *model = self.dataArray[indexPath.row];    
    YourCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];

    if ([self checkWhetherImageAlreadyExist]) {

        [cell.imageView setImage:model.image];

    } else {
        //show placeholder to avoid nothing in your UI, or your user gets confused
        [cell.imageView setImage:placeholderImage];
        [self startDownloadImageForIndexPath:indexPath];
    }
}

- (void)startDownloadImageForIndexPath:(NSIndexPath *)indexPath
{
    //YourImageDownloader is a class to fetch data from server
    //imageDownloadsInProgress is a NSMutableDictionary to record the download process, which can avoid repeat download
    YourImageDownloader *downloader = [self.imageDownloadsInProgress objectForKey:indexPath];

    if (downloader == nil) {
        YourDataModel *model = self.dataArray[indexPath.row];

        //configure downloader
        downloader = [[YourImageDownloader alloc] init];
        [downloader setURL:model.url];
        [downloader setCompletionHandler:^{
            //download the image to local, or you can pass the image to the block
            model.image = [UIImage imageWithContentsOfFile:model.localPath];
            YourCell *cell = [self.mCollectionView cellForItemAtIndexPath:indexPath];
            [cell.imageView setImage:model.image];

            //remove downloader from dictionary
            [self.imageDownloadsInProgress removeObjectForKey:indexPath];
        }];

        //add downloader to dictionary
        [self.imageDownloadsInProgress setObject:downloader forKey:indexPath];

        //start download
        [downloader startDownload];
    }
}

Verwenden Sie eine Klasse, um das Bild herunterladen. Wenn Sie viele Bilder in einer Sammlung anzuzeigen, können Sie prüfen, zu speichern, diese Bilder zu lokale im Fall von Speicher Warnung. wenn nun viele, lassen Sie einfach das Bild in den Speicher und zeigt Sie in Ihrer Sammlung anzeigen.

den code gefolgt ist, speichern Sie das Bild auf den lokalen und Lesen der Bilddaten aus der lokalen bei der Anzeige.

in .h:

#import <Foundation/Foundation.h>

@interface PortraitDownloader : NSObject

@property (nonatomic, copy) NSString *portraitName;
@property (nonatomic, copy) void (^completionHandler)(void);

- (void)startDownload;
- (void)cancelDownload;

@end

in .m

#import "PortraitDownloader.h"
#import <CFNetwork/CFNetwork.h>
#import "NSString+ImagePath.h" //it's a category to get the image local path

@interface PortraitDownloader ()

@property (nonatomic, strong) NSMutableData *activeDownload;
@property (nonatomic, strong) NSURLConnection *portraitConnection;

@end

@implementation PortraitDownloader

- (void)startDownload
{
    self.activeDownload = [NSMutableData data];

    NSString *urlstr = [NSString serverPortraitPathWithPortrait:self.portraitName];
    NSURL *url = [NSURL URLWithString:urlstr];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    self.portraitConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

- (void)cancelDownload
{
    [self.portraitConnection cancel];
    self.portraitConnection = nil;
    self.activeDownload = nil;
}

#pragma mark - NSURLConnectionDelegate

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.activeDownload appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    //Clear the activeDownload property to allow later attempts
    self.activeDownload = nil;

    //Release the connection now that it's finished
    self.portraitConnection = nil;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    //save to local path
    NSString *localSavePath = [NSString localPortraitPathWithPortrait:self.portraitName];
    [self.activeDownload writeToFile:localSavePath atomically:YES];

    self.activeDownload = nil;

    //Release the connection now that it's finished
    self.portraitConnection = nil;

    //call our delegate and tell it that our icon is ready for display
    if (self.completionHandler) {
        self.completionHandler();
    }
}

@end

wenn Sie möchten, lassen Sie Ihr Bild im Speicher, ändern Sie einfach die Fertigstellung block:

in .h

typedef void (^Completion_handle) (UIImage *image);

@interface PortraitDownloader : NSObject

@property (nonatomic, copy) Completion_handle myCompletionBlock;

und in .m

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    //get image from data
    UIImage *image = [UIImage imageWithData:self.activeDownload];

    self.activeDownload = nil;

    //Release the connection now that it's finished
    self.portraitConnection = nil;

    //call our delegate and tell it that our icon is ready for display
    if (self.myCompletionBlock) {
        self.myCompletionBlock(image);
    }
}

und auch Methoden modifizieren startDownloadImageForIndexPath, speichern Sie das Bild auf Ihr Modell zu behalten, es

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
 UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" forIndexPath:indexPath];
 UIImageView *imgView=[[UIImageView alloc]initWithImage:[UIImage imageNamed:@"profile_pic.png"]];
 NSMutableDictionary *contactData=[NSMutableDictionary new];
 contactData = [self.collectionData objectAtIndex:indexPath.row];
 imgView.image=[contactData objectForKey:@"image"];
 [cell addSubview:imgView];
 return cell;
}