iOS Delegate and Datasource


Example

The UITableViewDelegate is used to control how the table is displayed, and UITableViewDataSource is used to define the UITableView's data. There are two required methods and many optional ones which can be used to customize size, sections, headings, and cells in the UITableView.


UITableViewDataSource

Required Methods

numberOfRowsInSection: This method defines how many cells will be displayed in each section of the tableview.

Objective-C

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    // Return the number of rows for the table view. Usually populated from an array,
    // or can be statically defined.
    return self.myArray.count;
}

Swift 3

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // Return the number of rows for the table view. Usually populated from an array, 
    // or can be statically defined.
    return self.myArray.count
}

cellForRowAtIndexPath: This method is where the UITableView's cells are created and configured. Should return either a UITableViewCell or a custom subclass.

Note: Using dequeueReusableCellWithIdentifier:forIndexPath: requires that the class or nib has been registered for that identifier using the UITableView's registerClass:forCellReuseIdentifier: or registerNib:forCellReuseIdentifier: methods. Usually, this will be done in the UIViewController's viewDidLoad method.

Objective-C

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    MyCustomCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyCustomCell" 
                                                         forIndexPath:indexPath];
    
    // All additional customization goes here
    cell.titleLabel.text = [NSString stringWithFormat:@"Title Row %lu", indexPath.row];

    return cell;
}

Swift 3

func tableView(_ tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("MyCustomCell", forIndexPath:indexPath)
    
    // All additional customization goes here
    cell.titleLabel.text = String(format:"Title Row %lu", indexPath.row)
    
    return cell
}
Optional Methods

titleForHeaderInSection: Defines a string as the title for each section header in the table view. This method only allows for changing the title, further customization can be done by defining the view for the header.

Objective-C

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    switch(section) {
        case 0:
            return @"Title 1";
            break;

        case 1:
            return @"Title 2";
            break;

        default:
            return nil;
            break;
    }
}

Swift 3

func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    switch section {
        case 0:
            return "Title 1"
        case 1:
            return "Title 2"
        default:
            return nil
    }
}

titleForFooterInSection: Defines a string as the title for each section header in the table view.

Objective-C

- (NSString *)tableView:(UITableView *)tableView titleForFooterInSection:(NSInteger)section {
    return @"Footer text";
}

Swift 3

func tableView(_ tableView: UITableView, titleForFooterInSection section: Int) -> String? {
    return "Footer text"
}

canEditRowAtIndexPath: Used to determine if the editing UI should be displayed for the specified row. Should return YES if the specified row can be deleted or added.

Objective-C

- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}

Swift 3

func tableView(_ tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool {
    return true
}

commitEditingStyle:forRowAtIndexPath Should perform the work required to handle the addition or removal of the specified row. For example, remove the cell from the UITableView with animation, and remove the associated object from the table's data model.

Objective-C

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    switch (editingStyle) {
        case UITableViewCellEditingStyleInsert:
            // Insert new data into the backing data model here
            [self insertNewDataIntoDataModel];
            [tableView insertRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        case UITableViewCellEditingStyleDelete:
            [self removeDataFromDataModelAtIndex:indexPath.row];
            [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        default:
            // Nothing to perform if the editingStyle was neither Insert or Delete
            break;

    }
}

Swift 3

func tableView(_ tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
    switch editingStyle {
        case .Insert:
            self.insertNewDataIntoDataModel()
            tableView.insertRowsAtIndexPaths([indexPath], withRowAnimation:.Automatic)
        case .Delete:
            self.removeDataFromDataModelAtIndex(indexPath.row)
            tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation:.Automatic)
        default:
            // Nothing to perform if the editingStyle was neither Insert or Delete
    }
}

editActions:forRowAt Allows ability to add aditional actions or buttons to the edit mode of a row inside a UITableview. For example if you wanted two buttons, an edit and delete button when user swipes to edit the row, then you would use this method.

Swift 3

override func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath) -> [UITableViewRowAction]? {
    // In the handler you will get passed the action as well as the indexPath for 
    // the row that is being edited 
    let editAction = UITableViewRowAction(style: .normal, title: "Edit", handler: { [unowned self] action, indexPath in
        // Do something when edit is tapped
    })
    
    // Change the color of the edit action
    editAction.backgroundColor = UIColor.blue
        
    let deleteAction = UITableViewRowAction(style: .destructive, title: "Delete", handler: { [unowned self] action, indexPath in
        // Handel the delete event
    })
        
        
    return [deleteAction, editAction]
}

UITableViewDelegate

All methods in UITableViewDelegate are optional, but a delegate that implements them will enable extra features for the UITableView.

numberOfSectionsInTableView: By default this returns 1, but multiple section support is enabled by returning a different number of sections.

Objective-C

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return self.numSections;
}

Swift 3

func numberOfSectionsInTableView(_ tableView: UITableView) -> Int {
    return self.numSections
}

viewForHeaderInSection Allows the configuration of a custom view as the header for the section.

Objective-C

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, CGRectGetWidth(tableView.frame), 22)];
    view.backgroundColor = [UIColor groupTableViewBackgroundColor];
    
    UILabel *label = [[UILabel alloc] init];
    label.font = [UIFont systemFontOfSize:12];
    label.textColor = [UIColor darkGrayColor];
    
    switch (section) {
        case 1: {
            label.text = @"Title";
            label.frame = labelFrame;
            
            UIButton *more = [[UIButton alloc] initWithFrame:btnFrame];
            [more setTitle:@"See more" forState:UIControlStateNormal];
            [more.titleLabel setFont:[UIFont systemFontOfSize:12]];
            [view addSubview:more];
        }   break;
            
        default:
            label.frame = CGRectMake(0, 0, 0, 0);
            break;
    }
    
    [view addSubview:label];
    return view;
}

Swift 3

func tableView(_ tableView: UITableView,  viewForHeaderInSection section: Int) -> UIView? {
    let view = UIView(frame: CGRect(x: 0, y: 0, width: tableView.frame.size.width, height: 22))
    view.backgroundColor = UIColor.groupTableViewBackgroundColor()
    
    let label = UILabel()
    label.font = UIFont.systemFontOfSize(12)
    label.textColor = UIColor.darkGrayColor()
    
    switch section {
        case 1:
            label.text = "Title"
            label.frame = labelFrame
            
            let more = UIButton(frame: btnFrame)
            more.setTitle("See more", forState:.Normal)
            view.addSubview(more)
            
        default:
            label.frame = CGRect.zero
    }
    
    view.addSubview(label)
    return view;
}

heightForRowAtIndexPath: Define the height of each cell in the table view.

Objective-C

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return 44;
}

Swift 3

func tableView(_ tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
    return 44
}

heightForHeaderInSection: and heightForFooterInSection Define the height for the header and footer of each section in the table view

Objective-C

- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {
    return 33;
}

Swift 3

func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
    return 33
}