iPhone - 使UITableViewCells出现在NSURLConnection完成之前的视图加载

Question

我想使用故事板和JSON创建一个松散版本的LazyTabelImages。在我的主TableViewController的ViewDidLoad中，我启动一个NSURLConnection来获取JSON数据，但是我的单元格在连接完成之后才加载。我希望LazyTableImages具有相同的行为，其中单元格加载为空白，但是然后填充信息（重新加载表格数据）。如果我不使用storyboard，我可以复制它，因为LazyTables不使用storyboard，但这不是一个选项。

我已经浏览了LazyTableImages，试图找到解决方案，但故事板做出了很大的改变（无论如何）。

有没有简单的方法来获取单元格作为空白加载？例如，如果设备没有互联网，我仍然希望显示我的TableView，并且我会在该单元格中放置一条自定义消息。

代码：

我viewDidLoad中，我初始化连接的部分....

NSURLRequest *urlrequest = [NSURLRequest requestWithURL:[NSURL URLWithString:serverURL]]; 
    self.dataConnection = [[NSURLConnection alloc] initWithRequest:urlrequest delegate:self]; 

    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES; 

connectionDidFinnishLoading ...

- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{ 
    //ListData below is an array that my data received (JSON) is loaded into. It is then passed to getTableData. 
    self.dataConnection = nil; 
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
     [self performSelectorOnMainThread:@selector(getTableData:) withObject:ListData waitUntilDone:YES]; 
    }); 
} 

getTableData ...

-(void)getTableData:(NSData *)jsonData 
{ 
    NSError *error = nil; 
    arrayEntries = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableLeaves error:&error]; 
    for (int x = 0; x < arrayEntries.count; x++) 
    { 
     NSMutableDictionary *dic = [arrayEntries objectAtIndex:x]; 

     //ARecord is a class just like in LazyTableImages that creates objects to keep the icons/data together. The ARecords are loaded into the TableView 
     ARecord *arecord = [[ARecord alloc] init]; 

     NSString *title = [dic objectForKey:@"title"]; 
     NSString *subt = [dic objectForKey:@"subtitle"]; 
     NSString *url = [dic objectForKey:@"image_URL"]; 
     arecord.Icon = nil; 
     arecord.URL = url; 
     arecord.Name = title; 
     arecord.title = subt; 

     //this is where I load an array full of the arecord objects. 
     [array addObject:arecord]; 
    } 
    [self.tableView reloadData]; 
} 

Answer 1

我做了类似的事情。在viewDidLoad中：我将表数据的数组设置为[NSNull null]的几个对象，但是我要在下载数据时显示很多空行。在cellForRowAtIndexPath中：我检查是否[self.arrayOfTableData objectAtIndex：indexPath.row] = [NSNull null]。如果是这样，返回一个“空白”单元格，否则用ARRecrod数据加载单元格。 然后，当URL完成时，将您的ARRecords数组替换为NSNull数组。

Answer 2

因为我还没有看到你的代码，我只是给我的建议在这里：

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    dispatch_queue_t queue = dispatch_queue_create(NULL, NULL); 
    dispatch_async(queue, ^{ 

     //add your connection code here 
     //parse the json and store the data 
     // 

     dispatch_async(dispatch_get_main_queue(), ^{ 

      //here to reload your table view again, 
      //since UI related method should run on main thread. 

      [YOUR_TABLEVIEW reloadData]; 

     }); 

    }); 

    [YOUR_TABLEVIEW reloadData]; 
} 

注：请确保您在故事板的tableview已经连接到的代码！希望能帮助到你！

Answer 3

我这样做有两个对象。首先，我有一个图像获取器类，它可以异步下载数据，并在完成时通知委托人。然后我有一个图像视图类来实现fetcher的委托方法。因此，像：

@implementation AsyncImageFetcher 
-(id)initWithURL:(NSURL *)aURL andDelegate:(id<SomeProtocol>)aDelegate{ 

    //... 

    NSURLRequest *req = [NSURLRequest requestWithURL:aURL]; 
    //Note that NSURLConnection retains its delegate until the connection 
    //terminates! See comments in MyImageView below. 
    [NSURLConnection connectionWithRequest:req delegate:self]; 

    //... 
} 

//Implement standard connection delegates here. The important part is: 
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{ 

    // ... 

    UIImage *anImage = [self decodeDownloadedDataIntoAnImage]; 
    if([[self delegate] respondsToSelector:@selector(imageFetcher:didFetchImage:)]){ 
    [[self delegate] imageFetcher:self didFetchImage:anImage]; 
    } 

    //... 
} 

@end 

于是我继承UIImageView或UIView或东西（这取决于你如何灵活的需要来定），以实现委托协议和断火取出器：

@implementation MyImageView 

-(id)initWithURL:(NSURL *)aURL andPlaceHolderImage:(UIImage *)aPlaceHolder{ 

    //... 

    [self setImage:aPlaceHolder]; 

    //Note we don't assign this to an ivar or retain it or anything. 
    //That's ok because the NSURLConnection inside the fetcher actually 
    //retains the fetcher itself. So it will live until the connection 
    //terminates -- which is exactly what we want. Thus we disable 
    //CLANG's noisy warnings. 
    #pragma clang diagnostic push 
    #pragma clang diagnostic ignored "-Wunused-value" 
    [[AsyncImageFetcher alloc] initWithURL:aURL andDelegate:self]; 
    #pragma clang diagnostic pop 

    return self; 
} 


-(void)imageFetcher:(MCMAsyncImageFetcher *)anImageFetcher didFetchImage:(UIImage *)anImage{ 
    [self setImage:anImage]; 
} 

@end 

在您的具体例如，您只需在-tableView:cellForRowAtIndexPath:中设置一个MyImageView作为您单元格的imageView，当然会为其占位符和网址传递合理的值。