iOS UITableView中非同步載入圖片 － 解決方案

iOS UITableView中非同步載入圖片 － 解決方案

問題背景：

需要在UITableView中的每一行下載圖片，之前使用placeholder，下載好後存在cache中。

 

解決方案：

方案一：

 

如何安裝及使用在git頁面有詳細解釋，具體使用的代碼：

 

#import ...- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{    static NSString *MyIdentifier = @MyIdentifier;    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];    if (cell == nil)    {        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault                                       reuseIdentifier:MyIdentifier] autorelease];    }    // Here we use the new provided setImageWithURL: method to load the web image    [cell.imageView setImageWithURL:[NSURL URLWithString:@http://www.domain.com/path/to/image.jpg]                   placeholderImage:[UIImage imageNamed:@placeholder.png]];    cell.textLabel.text = @My Text;    return cell;}

 

 

方案二：

使用iOS自有的非同步多線程，下載好圖片後存入cache，再使用delegate函數更新tableview：

- (void)reloadRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation

 

初始化：

 

@interface ViewController ()@property (strong, nonatomic)  NSMutableArray *imageArray;@property (strong, nonatomic) NSCache *imageCache;@property (weak, nonatomic) IBOutlet UITableView *myCustomTableView;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];        self.imageCache = [[NSCache alloc] init];}

TableView delegate函數：

 

 

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {    return 1;}- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {    // Number of rows is the number of time zones in the region for the specified section.    return 32;}- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {    NSLog(@cellForRowAtIndexPath %d, indexPath.row);        static NSString *MyIdentifier = @customIdentifier;    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];    if (cell == nil) {        cell = [[CustomTableViewCell alloc] initWithStyle:UITableViewCellStyleDefault  reuseIdentifier:MyIdentifier];    }        if ([cell isKindOfClass:[CustomTableViewCell class]])    {        CustomTableViewCell *customCell = (CustomTableViewCell *)cell;        NSData *imageData = [self.imageCache objectForKey:[NSString stringWithFormat:@%d, indexPath.row]];                if(imageData != nil){            customCell.customImageView.image = [UIImage imageWithData:imageData];        }        else{            customCell.customImageView.image = [UIImage imageNamed:@test1];                        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, (unsigned long) NULL), ^(void){                UIImage *image = [self getPictureFromServer];                                if (image != nil) {                    NSData *tmpImageData = UIImagePNGRepresentation(image);                    [self.imageCache setObject:tmpImageData forKey:[NSString stringWithFormat:@%d, indexPath.row]];                    NSLog(@download image for %d, indexPath.row);                                        [self performSelectorOnMainThread:@selector(reloadTableViewDataAtIndexPath:) withObject:indexPath waitUntilDone:NO];                }                else{                    // do nothing ..                }            });        }    }    else{        // do nothing ..    }    return cell;}

reloadTableViewDataAtIndexPath：

 

 

- (void) reloadTableViewDataAtIndexPath: (NSIndexPath *)indexPath{    NSLog(@MyWineViewController: in reload collection view data for index: %d, indexPath.row);    NSArray* indexArray = [NSArray arrayWithObjects:indexPath, nil];    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationFade];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationAutomatic];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationBottom];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationLeft];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationMiddle];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationNone];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationRight];//    [self.myCustomTableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationTop];}

 

下載圖片

 

- (UIImage *) getPictureFromServer{    UIImage *image = nil;    NSString *urlString = [NSString stringWithFormat:@http://yourPicture.jpg];        NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];    [request setURL:[NSURL URLWithString:urlString]];    [request setHTTPMethod:@GET];        NSURLResponse *response;    NSError *connectionError;    NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&connectionError];    if (connectionError == NULL) {        NSInteger statusCode = [(NSHTTPURLResponse *)response statusCode];        NSLog(@getPictureFromServer - Response Status code: %ld, (long)statusCode);                if (statusCode == 200) {            image = [UIImage imageWithData:returnData];        }        else{            // do nothing..        }    }    else{        // do nothing..    }        return image;}

 

方案三：（不推薦）

在方案二的基礎上，變動在於下載好圖片後load整個tableview，缺點時會引起滑動tableview時阻塞。

 

- (void) reloadTableViewData{    NSLog(@MyWineViewController: in reload collection view data);    [self.myCustomTableView reloadData];}

參考連結：

 

http://stackoverflow.com/questions/15290974/uitableview-on-screen-image-download-lazy-loading

http://stackoverflow.com/questions/7040740/reload-spefic-uitableview-cell-ios