Question

I have created a custom view that contains a UIPickerView and a UITableViewCell to display the contents currently selected in the picker. My PickerViewController is set as both the delegate and dataSource of the picker, and I have implemented numberOfComponentsInPickerView:, pickerView: numberOfRowsInComponent:, and pickerView: titleForRow: forComponent:, but the picker appears blank when the program is run, and thanks to placing NSLog calls in the methods, I’ve discovered that the methods are never getting called. I have no idea what the issue is, as the picker appears to be linked up correctly with the PickerViewController.

For the basic functionality that I’m trying to achieve, look at the “Start & End” view in the iOS Calendar app. I am trying to imitate this exactly, but only using one UITableViewCell instead of three.

PickerViewController.h

#import <UIKit/UIKit.h>

@interface PickerViewController : UIViewController

@property (weak, nonatomic) IBOutlet UITableViewCell *pickerSelection;
// Property to dynamically determine what content to display in the picker.
@property (nonatomic) BOOL userIsChoosingClass;

@end

viewDidLoad

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(self.thePicker.delegate.description);
    if (self.userIsChoosingClass) {
        self.pickerSelection.textLabel.text = @"Class";
    } else {
        self.pickerSelection.textLabel.text = @"Major";
    }
}

Picker View Data Source Methods

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView {
    return 1;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView
numberOfRowsInComponent:(NSInteger)component {
    size_t numberOfRows = 0;

    if (self.userIsChoosingClass) {
        numberOfRows = [self.brain classChoicesForSignUp].count;
    } else {
        numberOfRows = [self.brain majorChoicesForSignUp].count;
    }

    return numberOfRows;
}

Picker View Delegate Methods

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row
            forComponent:(NSInteger)component {
    NSLog(@"Picker view delegate method called");
    NSString *title;

    if (self.userIsChoosingClass) {
        title = [[self.brain classChoicesForSignUp] objectAtIndex:row];
    } else {
        title = [self.majorChoices objectAtIndex:row];
    }

    return title;
}

Answer 1

If your numberOfRows… datasource method is returning 0, then your delegate method will never be called – the picker won’t ask for the title of a row if it doesn’t think it has any rows to display.