即使我已设置PickerView，也没有任何选项

Question

I have a UIPickerView, and it is showing up, but it just shows (null). Why is this? I have it conformed to the delegate's I need in.

EDIT: more detail.

Basically, my app is a flight logbook. You make planes, which you saves, and you can pick it when you make a new session. The planeNum key stores how many planes there are, and the key Plane%liTailNumber has the tail number for that plane.

This is my code:

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

- (NSInteger)pickerView:(UIPickerView *)thePickerView numberOfRowsInComponent:(NSInteger)component {
    return (long)[[NSUserDefaults standardUserDefaults]integerForKey:@"planeNum"];
}

NSMutableArray *tailPickerOptions;

- (NSString *)pickerView:(UIPickerView *)thePickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component {

    NSInteger num = [[NSUserDefaults standardUserDefaults]integerForKey:@"planeNum"];

    while (num > 0){
        --num;
        tailPickerOptions = [[NSMutableArray alloc]init];
        NSString *dTailNumber = [NSString stringWithFormat:@"%@", [[NSUserDefaults standardUserDefaults]objectForKey:[NSString stringWithFormat:@"Plane%liTailNumber", (long)num]]];
        [tailPickerOptions addObject:dTailNumber];
        NSLog(@"%@", tailPickerOptions);
    }
    return tailPickerOptions[row];
}

Answer 1

You initialize a new array for each loop of the while. Your code also doesn't ensure you actually initialize the array - if num = 0, you'll never go in and declare the array. There should be a warning or compiler error for this. In the best case scenario because you keep declaring a new array in your loop, you'll return a max of 1 element ever.

Move your array declaration above the while loop.