Question

How do I pass the touches events down to my viewcontroller? I think the UIScrollView is interecepting the touches and causeing the touches events that I have in the view controller not to fire

Code snippet:

    //
//  DragDrop.m
//  Ballet
//
//  Created by  on 1/10/12.
//  Copyright (c) 2012 __MyCompanyName__. All rights reserved.
//

#import "DragDrop.h"
#import "BAScrollView.h"

@implementation DragDrop

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization

        [self.view setBackgroundColor:[UIColor whiteColor]];
    }
    return self;
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView
{
}
*/


// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad
{
    [super viewDidLoad];

    sv = [[BAScrollView alloc] initWithFrame:self.view.frame];


    [sv setBackgroundColor:[UIColor redColor]];

    UIImageView *dragImage2 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"img-thumb-10-mindful.png"]];

    [dragImage2 setUserInteractionEnabled:YES];

    dragImage2.frame = CGRectMake(0, 0, 64, 64);

    [sv addSubview:dragImage2];


    [self.view addSubview:sv];

    //this image works as expected
    UIImageView *dragImage3 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"img-thumb-10-mindful.png"]];

    [dragImage3 setUserInteractionEnabled:YES];

    dragImage3.frame = CGRectMake(200, 200, 64, 64);

    [self.view addSubview:dragImage3];
}


- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event allTouches] anyObject];

    if ([touch.view isKindOfClass:[UIImageView class]])
    {
        dragImage = [[UIImageView alloc] initWithImage:((UIImageView *)(touch.view)).image];
        dragImage.frame = CGRectMake(100, 100, 64, 64);//touch.view.frame;
        [dragImage setUserInteractionEnabled:YES];
      //  CGPoint point = [[[event allTouches] anyObject] locationInView:super.view];

        //dragImage.frame = 
       // dragImage.center = point;
        [self.view addSubview:dragImage];



    }



}


-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{

    NSLog(@"MOVED");

    if (dragImage!=nil) {
        CGPoint point = [[[event allTouches] anyObject] locationInView:self.view];

        dragImage.center = point;
    }





}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    if (dragImage != nil)
    {

        [dragImage removeFromSuperview];
        [dragImage release];
        dragImage = nil;
    }
}


@end

• the SCROLLVIEW SUB-CLASS

//
// BAScrollView.m
// Ballet
//
// Created by n 1/10/12.
// Copyright (c) 2012 MyCompanyName. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "BAScrollView.h"

@implementation BAScrollView

- (id)initWithFrame:(CGRect)frame 
{
    return [super initWithFrame:frame];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self.nextResponder touchesBegan:touches withEvent:event]; 


}


- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self.nextResponder touchesMoved:touches withEvent:event]; 
}

- (void)touchesEnded: (NSSet *) touches withEvent: (UIEvent *) event 
{   
    // If not dragging, send event to next responder
    if (!self.dragging) 
        [self.nextResponder touchesEnded: touches withEvent:event]; 
    else
        [super touchesEnded: touches withEvent: event];
}



@end

Answer 1

There is a good article about Responder Chain by Jeff Lamarche

In your case, you can subclass your scroll view and delegate your touch event to the next one in the responder chain.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    if(condition) // you want scroll to happen
        [super touchesBegan:touches withEvent:event];
    else // you want to delegate your touch to the next responder
        [self.nextResponder touchesBegan:touches withEvent:event];
}

This is not tested code, but I hope you get the idea.