Determine one column value from another column in pickerview

Question

I am working on a picker view with 3 columns. I want to determine the 3rd column value from the second column. Here is part of my code

- (void)viewDidLoad {
    [super viewDidLoad];

    Number=@[@"Trans",@"1st",@"2nd",@"3rd",@"4th",@"5th",@"6th",@"7th",@"8th",@"9th",@"10th",@"11th",@"12th"];
    Season=@[@"Spring",@"Summer",@"Fall"];
    Course=@[@"CHEM1100 General Chem I",@"CHEM2100 General Chem II",@"CHEM3511 Org Chem",@"CHEM3521 Org Chem II"];

   // Course=@[@"Summer1",@"Summer2",@"Summer3"];

    Course = [Course sortedArrayUsingSelector:@selector(compare:)];
    Number =[Number sortedArrayUsingSelector:@selector(compare:)];
    Season =[Season sortedArrayUsingSelector:@selector(compare:)];


}

Here is my question, how can I achieve the goal like

if (Season==@"Spring")
Course= @[@"CHEM1100 General Chem I",@"CHEM2100 General Chem II",@"CHEM3511 Org Chem",@"CHEM3521 Org Chem II"];
else if (Season==@"Summer")
Course=@[@"Summer1",@"Summer2",@"Summer3"];

Sorry, I don't know what method to use to complete the code. Any idea please?

To show the column value, I use the following code:

- (IBAction)addCourse:(UIButton *)sender {

    NSInteger numRow=[picker selectedRowInComponent:kNumComponent];//0=1st,1=2nd,etc
    NSInteger SeaRow=[picker selectedRowInComponent:kSeaComponent];//0=fall,1=spring,2=summer
    NSInteger CourseRow=[picker selectedRowInComponent:kCourseComponent];

   NSString *num=Number[numRow];
   NSString *season=Season[SeaRow];
    NSString *course=Course[CourseRow];

    NSString *msg=[[NSString alloc ]initWithFormat:@"%@ ",course];
    _courseLabel.text=[msg substringToIndex:8]; 

}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{

    if (component==kNumComponent)
        return [Number count];
        else if(component==kSeaComponent)
            return [Season count];
        else return [Course count];

}

Answer 1

According to the documentation, you must provide your UIPickerView with a datasource and a delegate. The datasource tells the view how many components and rows there are, while the delegate tells it the content of the components row. Let us suppose that you implement titleForRow: in your delegate. Since this is going to change based on a selection, you will need to do two things: (i) make sure your delegate object knows which selection was made (e.g. @"Spring") and (ii) you will then need to call the UIPickerView reloadComponent: method so that your delegate's titleForRow: method will be called.

Example: suppose your action method is componentSelected:

-(void)componentSelected:(id)sender
{
    NSInteger row = [myPicker selectedRowInComponent:seasonComponent];
    myDelegate.season = row;
    [myPicker reloadComponent:courseComponent];
}

By the way, it is worth getting into the habit of being very careful with "=", "==", isEqualToString: etc. to avoid bugs. Your question has several basic syntactical errors. The line

if(season = @"spring")

should be

if([season isEqualToString:@"spring"]);

not just because "=" is assignment, but because "==" makes no sense if one of the arguments is a literal (it is essentially pointer comparison). isEqualToString will compare the target string with the argument string.