Question

I created 2 UIPickerView Programatically. How do I make sure to hide pickerView1 when pickerView2 is about to show. Vice versa.

Thank you.

This is how I created them.

  - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
if (indexPath.row == 1){
            [scrollView setContentOffset:CGPointMake(0, 223) animated:YES];
            CGRect pickerFrame = CGRectMake(0, 152, 0, 0);

            UIPickerView *pickerView1 = [[UIPickerView alloc] initWithFrame:pickerFrame];
            pickerView1.showsSelectionIndicator = YES;
            pickerView1.dataSource = self;
            pickerView1.delegate = self;
            [pickerView1 setTag:1];
            [self.view addSubview:pickerView1];
            [pickerView1 release];
            [tableView deselectRowAtIndexPath:indexPath animated:YES];

        }
        else if (indexPath.row == 2){
            [scrollView setContentOffset:CGPointMake(0, 273) animated:YES];
            CGRect pickerFrame = CGRectMake(0, 152, 0, 0);

            UIPickerView *pickerView2 = [[UIPickerView alloc] initWithFrame:pickerFrame];
            pickerView2.showsSelectionIndicator = YES;
            pickerView2.dataSource = self;
            pickerView2.delegate = self;
            [pickerView2 setTag:2];
            [self.view addSubview:pickerView2];
            [pickerView2 release];
            [tableView deselectRowAtIndexPath:indexPath animated:YES];
        }
    }

Answer 1

In your viewDidLoad:

[pickerView1 setAlpha:1.0];
[pickerView2 setAlpha:0.0];

Where pickerView1 is visible whereas pickerView2 is not.

And wherever you want to display pickerView2 whilst hiding pickerView1 – just reverse the above.

[pickerView1 setAlpha:0.0];
[pickerView2 setAlpha:1.0];

There are other ways of doing this but this is my preferred way of doing it.

UPDATE:

Here’s how you would implement it using your code:

 - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    if (indexPath.row == 1){
        [scrollView setContentOffset:CGPointMake(0, 223) animated:YES];
        CGRect pickerFrame = CGRectMake(0, 152, 0, 0);

        if (pickerView1 == nil) { //<--- You don't need to keep calling alloc and init. This if statement only calls if you have not already declared pickerView1.
            UIPickerView *pickerView1 = [[UIPickerView alloc] initWithFrame:pickerFrame];
            pickerView1.showsSelectionIndicator = YES;
            pickerView1.dataSource = self;
            pickerView1.delegate = self;
            [pickerView1 setTag:1];
            [self.view addSubview:pickerView1];
        }

        [pickerView1 setAlpha:1.0]; //<--- New Code
        if (pickerView2 != nil) { //<-- Checking if pickerView2 is declared yet, if not then it is already invisible. ;)
            [pickerView2 setAlpha:0.0];
        }

        //removed release call - add to dealloc method
        [tableView deselectRowAtIndexPath:indexPath animated:YES];

    }
    else if (indexPath.row == 2){
        [scrollView setContentOffset:CGPointMake(0, 273) animated:YES];
        CGRect pickerFrame = CGRectMake(0, 152, 0, 0);

        if (pickerView2 == nil) { //<-- again, no need to always alloc and init
            UIPickerView *pickerView2 = [[UIPickerView alloc] initWithFrame:pickerFrame];
            pickerView2.showsSelectionIndicator = YES;
            pickerView2.dataSource = self;
            pickerView2.delegate = self;
            [pickerView2 setTag:2];
            [self.view addSubview:pickerView2];
        }

        [pickerView2 setAlpha:1.0]; //<--- New Code
        if (pickerView1 != nil) { //<-- Checking if pickerView1 is declared yet, if not then it is already invisible. ;)
            [pickerView1 setAlpha:0.0];
        }
        //add release call to dealloc method
        [tableView deselectRowAtIndexPath:indexPath animated:YES];
    }
}

UPDATE 2:

Try this:

In your header (.h) file add this:

    @interface <name>ViewController : UIViewController <UIPickerViewDelegate, UIPickerViewDataSource> {
        UIPickerView *pickerView1;
        UIPickerView *pickerView2;
    }
    @property (nonatomic, retain) UIPickerView *pickerView1;
    @property (nonatomic, retain) UIPickerView *pickerView2;
    @end

You have to declare your pickerViews here for my previous code to work. Also note the <UIPickerViewDelegate, UIPickerViewDataSource> protocols.

Back in your implementation (.m) file, remember to synthesize:

@synthesize pickerView1;
@synthesize pickerView2;

And in - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath replace:

UIPickerView *pickerView1 = [[UIPickerView alloc] initWithFrame:pickerFrame];

with

pickerView1 = [[UIPickerView alloc] initWithFrame:pickerFrame];

And replace:

UIPickerView *pickerView2 = [[UIPickerView alloc] initWithFrame:pickerFrame];

with:

pickerView2 = [[UIPickerView alloc] initWithFrame:pickerFrame];

Just remember to release them in your dealloc method:

    - (void)dealloc {
        [pickerView1 release];
        [pickerView2 release];
        [super dealloc];
    }

Your undeclared problem should be solved now.