iOS - Scrolling two UITextViews simultaneously

Question

I've done some looking around but I haven't been able to find anything that clearly explains how I could simultaneously scroll two un-editable UITextViews. I think I may need to use either scrollRangeToVisible , or setContentOffset , though I could not get either of them to work.

Does anyone have any examples/samples, or documentation regarding this that they could point me towards?

EDIT: To clarify, I would like to be able to scroll one UITextView, and have the changes as a result of the scrolling reflected on a second UITextView as well.

Thanks!

Answer 1

Use the UIScrollViewDelegate methods to get information about scroll actions of the first scroll view and then scroll the second programmatically like that:

- (void) scrollViewDidScroll:(UIScrollView *)view1 {
    scrollView2.contentOffset = view1.contentOffset;
}

Answer 2

Just continuing with previous answers, to give some more information, I generated this code:

In the interface (.h):

#import <UIKit/UIKit.h>

@interface DoubleTextViewController : UIViewController <UITextViewDelegate>

@property (strong, nonatomic) IBOutlet UITextView *textView1;
@property (strong, nonatomic) IBOutlet UITextView *textView1;

@end

In your implementation (.m):

Use this viewDidLoad function after defining the corresponding properties and global variables.

#import "DoubleTextViewController.h"

#define TEXT_VIEW_1_TAG 1001
#define TEXT_VIEW_2_TAG 1002

@interface DoubleTextViewController () {

    BOOL isScrolling;
}

@end

@implementation DoubleTextViewController

@synthesize textView1, textView2;

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view..

    isScrolling = NO;

    [self.textView1 setTag:TEXT_VIEW_1_TAG];
    [self.textView2 setTag:TEXT_VIEW_2_TAG];

    [self.textView1 setDelegate:self];
    [self.textView2 setDelegate:self];
}

And add this function for simultaneous scroll.

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {

    if (isScrolling) {
        return;
    }


    isScrolling = YES;

    if (scrollView.tag == TEXT_VIEW_1_TAG) {

        [self.textView2 setContentOffset:scrollView.contentOffset animated:NO];

    } else if (scrollView.tag == TEXT_VIEW_2_TAG) {

        [self.textView1 setContentOffset:scrollView.contentOffset animated:NO];
    }

    isScrolling = NO;
}

As proposed by Hermann Klecker, the isScrolling variable stops scrolling loops and makes the user experience nicer. Using the code proposed by Fabian Kreiser makes the scroll stops as soon as the user leaves the finger, making it strange.

Answer 3

React in

- (void)scrollViewDidScroll:(UIScrollView *)scrollView{

and set the other's scrollView setContentVisible according to scrollView.contentOffset .

Just be aware that some methods of UIScrollView will invoke scrollViewDidScroll even if called programmatically. This applies to scrollRangeToVisible and will end up in a loop unless you take action to prevent this loop. I don't think that setContentOffset or setting scrollView2.contentOffset = CGPointMake(..,..) does call scrollViewDidScroll . However, I would not sign this in blood. Be prepared to see a loop and take actions to avoid it. (such as boolean instance variable set before calling setContentOffset and re-set in scrollViewDidScroll followed by return; )