Lazy Load cell image for programmatically created tableview

问题

I am creating a number of tableviews programmatically. The client has specifically asked for a layout that is not a UITableView Controller. Something like:

The number of tableviews as well as the number of items in each table varies. All of the tables are created at once when the view loads. I would like to add thumbnails to the cells in the table views. I need find a way to lazy load the thumbnails. I have successfully implemented a lazy load on a UITableViewController. My prior success is in part because I can use the [tableview reloadData] call to indicate the cell thumbnails can be displayed after the images have been cached. How might I implement a lazy load to the tableviews created programmatically? My initial idea is to add some sort of selector to the table view in order to update a cell once the images have been cached for a particular cell. I am not sure how this would work and would appreciate any help.

The following is the code that I use to create the table views programmatically (I am using ARC):

@interface SyllabusSegmentedViewController : UIViewController <UITableViewDelegate, UITableViewDataSource>

@property (nonatomic, weak)IBOutlet UIScrollView *SyllabusSegmentedSV;

--

@implementation SyllabusSegmentedViewController

- (void) viewWillAppear:(BOOL)animated {
   [super viewWillAppear:animated];

   // Programmatic creation of the table views and titles for Table Views 
   [self ProgramaticCreationOfTableView:self];
}

-(void) ProgramaticCreationOfTableView:(id)sender {
    for (numTableViews = 0; numTableViews < [syllabusDispayed.LevelNames count]; numTableViews ++) {

    // Create Table View
    UITableView *newTableView = [[UITableView alloc] init];
    newTableView = [self createTableView:self];

    // Create UILabel that will act as Title for Each table view
    UILabel *newLabel = [[UILabel alloc] initWithFrame:[self MakeHeaderLabelFrame:numTableViews workingTableView:newTableView]];
    [newLabel setBackgroundColor:nil];
    newLabel.backgroundColor = [UIColor colorWithRed:(204/255.0) green:(204/255.0) blue:(204/255.0) alpha:1.0];
    newLabel.text = [syllabusDispayed.LevelNames objectAtIndex:numTableViews];
    newLabel.textAlignment = NSTextAlignmentCenter;
    UIFont *font = [UIFont boldSystemFontOfSize:20];
    UIColor *color = [UIColor darkGrayColor];
    newLabel.font = font;
    newLabel.textColor = color;


    [newTableView setBackgroundView:nil];
    newTableView.backgroundColor = [UIColor colorWithRed:(204/255.0) green:(204/255.0) blue:(204/255.0) alpha:1.0];
    newTableView.scrollEnabled = NO;

    newTableView.frame = ([self MakeTableViewFrame:numTableViews workingTableView:newTableView]);

    newTableView.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin;
    newLabel.autoresizingMask     = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin;

    [SyllabusSegmentedSV addSubview:newTableView];
    [SyllabusSegmentedSV addSubview:newLabel];
    }
  }

-(UITableView *)createTableView:(id)sender {
    UITableView *tableView = [[UITableView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame] style:UITableViewStyleGrouped];
    tableView.delegate = self;
    tableView.dataSource = self;
    tableView.accessibilityLabel = [NSString stringWithFormat:@"%d", numTableViews];

    return tableView;
 }

-(CGRect)MakeHeaderLabelFrame:(int)workingTableNumber workingTableView:(UITableView *)newTableView {
    int numberOfPreviousLevelsRows = 0;

    for (int i = 0; i < workingTableNumber ; i ++) {
    numberOfPreviousLevelsRows += [[syllabusDispayed.SyllabusDictionary objectForKey:[syllabusDispayed.LevelNames objectAtIndex:i]] count];
    }

    return CGRectMake(0, 75 + ((workingTableNumber * 80) + (numberOfPreviousLevelsRows *55)), self.view.bounds.size.width, 25);
 }


-(CGRect)MakeTableViewFrame:(int)workingTableNumber workingTableView:(UITableView *)newTableView {
    int numberOfPreviousLevelsRows = 0;

     for (int i = 0; i < workingTableNumber ; i ++) {
     numberOfPreviousLevelsRows += [[syllabusDispayed.SyllabusDictionary objectForKey:[syllabusDispayed.LevelNames objectAtIndex:i]] count];
     }

    return CGRectMake(0, 95 + ((workingTableNumber * 80) + (numberOfPreviousLevelsRows *55)), self.view.bounds.size.width, 65*[newTableView numberOfRowsInSection:0]);
 }

I also have implemented the necessary function for a UITableViewDelegate such as

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

 - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath 

回答1:

Take a look at library SDWebImage

I think this is what you are looking for.

But may be the real problem with your approach: i guess that it is not really necessary to create multiple TableViews that located one after another - it's case where sections may do the thing.

EDIT

TableViewDataSource has method named – numberOfSectionsInTableView:.

Also by implementing – tableView:heightForHeaderInSection: or – tableView:heightForFooterInSection: you can get necessary space between sections.

You should implement all this methods in SyllabusSegmentedViewController.

来源：https://stackoverflow.com/questions/18083866/lazy-load-cell-image-for-programmatically-created-tableview