How to subclass a UITextView: Implement a horizontal swipe

Question

I'm trying to implement a horizontal scroll on an UITextView. I found this explained here.

However, I don't understand how I can 'subclass' a UITextView. The code which is given and which I tried to implement is the following:

@interface SwipeableTextView : UITextView {
}

@end

@implementation SwipeableTextView

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

    [self.superview touchesBegan:touches withEvent:event];

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

    [self.superview touchesMoved:touches withEvent:event];
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesEnded:touches withEvent:event];

    [self.superview touchesEnded:touches withEvent:event];
} 

@end

Apparently, this is supposed to override a normal UITextView which I can then call by referring to SwipeableTextView (e.g. SwipeableTextView.text = @"Some Text";). My question is, where do I put this piece of code? In my .m or .h file? I tried to put it beneath the implementation section of my m file, but this won't work as I already have an @interface and @implementation section. Any help would be very much appreciated.

EDIT: This works now:

//
//  SwipeTextView.h
//  Swipes
//

#import <Foundation/Foundation.h>

@interface SwipeTextView : UITextView {
    CGPoint     gestureStartPoint;
}

@property CGPoint gestureStartPoint;


@end

M File

//
//  SwipeTextView.m
//  Swipes
//

#import "SwipeTextView.h"
#define kMinimumGestureLength    10
#define kMaximumVariance         5

@implementation SwipeTextView
@synthesize gestureStartPoint;

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

    UITouch *touch =[touches anyObject];
    gestureStartPoint = [touch locationInView:self.superview];

    [self.superview touchesBegan:touches withEvent:event];

}

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

    [super touchesMoved:touches withEvent:event];
    [self.superview touchesMoved:touches withEvent:event];

    UITouch *touch = [touches anyObject];
    CGPoint currentPosition = [touch locationInView:self.superview];

    CGFloat deltaXX = (gestureStartPoint.x - currentPosition.x); // positive = left, negative = right
    //CGFloat deltaYY = (gestureStartPoint.y - currentPosition.y); // positive = up, negative = down

    CGFloat deltaX = fabsf(gestureStartPoint.x - currentPosition.x); // will always be positive
    CGFloat deltaY = fabsf(gestureStartPoint.y - currentPosition.y); // will always be positive

    if (deltaX >= kMinimumGestureLength && deltaY <= kMaximumVariance) {
        if (deltaXX > 0) {
            NSLog (@"Horizontal Left swipe detected");
        }
        else {
            NSLog(@"Horizontal Right swipe detected");
        }

    }

}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesEnded:touches withEvent:event];

    [self.superview touchesEnded:touches withEvent:event];
} 




@end

And finally, this is how I create the subclass of this custom UITextView in my ViewController:

// UITextView
CGRect aFrame = CGRectMake(0, 100, 320, 200);
aSwipeTextView = [[SwipeTextView alloc] initWithFrame:aFrame];
aSwipeTextView.text = @"Some sample text. Some sample text. Some sample text.";
[self.view addSubview:aSwipeTextView];

See [MPTextView](http://miphol.com/muse/2009/05/subclassing-uitextview.html) Might give you a hint. — Ahmad Kayyali, Apr 18 '11 at 15:06
@AhmadTK: In other words, I simply make a new m and h file and then #import it into the code where I wish to use MPTextView? Thanks for the link! — n.evermind, Apr 18 '11 at 15:19
Just Drag them to your project and YES Import **MPTextView.h** — Ahmad Kayyali, Apr 18 '11 at 15:21

score 5 · Accepted Answer · answered Apr 18 '11 at 15:19

5

Ok this is what you do.

When you want to subclass an object you create .h and .m files for it so.

Create a file called SwipeableTextView.h and insert this code inside:

#import <Foundation/Foundation.h>

    @interface SwipeableTextView : UITextView {

    }

@end

Then create a file SwipeableTextView.m and inser this into it:

#import "SwipeableTextView.h"

@implementation SwipeableTextView

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

    [self.superview touchesBegan:touches withEvent:event];

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

    [self.superview touchesMoved:touches withEvent:event];
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesEnded:touches withEvent:event];

    [self.superview touchesEnded:touches withEvent:event];
} 

@end

To use this new sublass in your project do the following.

import the header:

#import "SwipeableTextView.h"

and then instead creating the UITextView normaly you would create SwipeableTextView like this:

SwipeableTextView *sTextView = [[SwipeableTextView alloc] init];

That's it. Hope it helps.

answered Apr 18 '11 at 15:19

Cyprian

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Excellent explanation! I was starting to guess this from the comment provided by AhmadTK, but this is truly helpful. Thanks so much! – n.evermind Apr 18 '11 at 15:20
I was successful in implementing this. However, I still can't see how I can now achieve horizontal scrolling in an UITextView. Will I need to implement this method in the SwipeableTextView.m file or will I need to do this in my viewDelegate? I am talking about modifying the - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { and - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { – n.evermind Apr 18 '11 at 16:31
1

You should do it in the custom subclass declaration in file "SwipeableTextView.m". Basically if you want custom behavior of any kind on a standard object you need to subclass it like you did with SwipeableTextView and write all the custom behavior in that class. Or you can do some cool stuff using "[Categories](http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocCategories.html)" and extending the capabilities of standard object that way. – Cyprian Apr 18 '11 at 18:36
@Cyprian: Thanks so much. I tried this, but it still doesn't detect my swipes. I posted the updated code above. Perhaps you could have a quick look. I guess `gestureStartPoint = [touch locationInView:self.superview];` is the problem -- I am not sure about 'superview'. I tried it with self, but that didn't work either. I simply don't get the any response in the console. – n.evermind Apr 18 '11 at 19:09
1

@n.evermind. You have a lot of logic errors in your code. I can see you are going blind on this. One of the problem is that you never use your subclass instead of this initialization `aSwipeTextView = [[UITextView alloc] initWithFrame:aFrame];` use the following `aSwipeTextView = [[SwipeTextView alloc] initWithFrame:aFrame];` By the way UITextView supports horizontal scrolling so, why would you want to do it yourself? Read docs for UITextView. – Cyprian Apr 18 '11 at 20:06
Ah... that fixed it. What are the other logic errors (only if you can be bothered to tell me, otherwise, don't worry). I wasn't aware that UITextView supports horizontal scrolling - I'll read up the docs and see if there is an easier way to do this. Thanks so much again for your time, you've been truly helpful. – n.evermind Apr 18 '11 at 20:14

How to subclass a UITextView: Implement a horizontal swipe

1 Answers1