Defining maximum variance of an UITextView

问题:

If you have a normal UITextView with loads of text in it you can swipe up and down:

• if you swipe left or right in a very horizontal line, nothing will happen
• if you swipe left or right with a very slight angle, you will swipe up or down

So there is obviously some kind of class definition which tells the UITextView when to react to a swipe and when not to. Something like a maximumVariance constant, I guess.

My problem is that I'm trying to subclass an UITextView to enable left/right swipe. However, you will need to swipe in a pretty straight line, otherwise, you'll get an up or down swipe. So my question is if there is someway to re-define the standard variance variable of an UITextView?

Here is my subclass .m file. Note that the kMaximumVariance doesn't really have any effect as this is overwritten by whatever variance the standard UITextView class provides:

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

#import "SwipeTextView.h"
#import "PageView.h"

#define kMinimumGestureLength    15
#define kMaximumVariance         100

@implementation SwipeTextView
@synthesize delegate, gestureStartPoint;


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

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

}

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

    [super touchesMoved:touches withEvent:event];


}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    [super touchesEnded:touches withEvent:event];
    [self resignFirstResponder]; // this hides keyboard if horizonal swipe

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

    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


    NSLog(@"deltaXX (%.1f) deltaYY (%.1f) deltaX (%.1f) deltaY (%.1f)",deltaXX, deltaYY, deltaX, deltaY);

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

    }



} 




@end

EDIT:

Suggestion to cancel touches reaching UITextView (see below):

// Prevent recognizing touches
- (BOOL)gestureRecognizer:(UISwipeGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch {

    if ([gestureRecognizer direction] == UISwipeGestureRecognizerDirectionLeft) {
        // Left swipe: I want to handle this
        return YES;
    }
    if ([gestureRecognizer direction] == UISwipeGestureRecognizerDirectionRight) {
        // Right swipe: I want to handle this
        return YES;
    }
    if ([gestureRecognizer direction] == UISwipeGestureRecognizerDirectionUp) {
        // Up swipe: textView needs to handle this
        return NO;
    }
    if ([gestureRecognizer direction] == UISwipeGestureRecognizerDirectionDown) {
        // Down swipe: textView needs to handle this
        return NO;
    } else
        return YES;
}


-(void)viewDidLoad
{

    UITapGestureRecognizer *GesRec = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(doSomething:)];

    [GesRec setCancelsTouchesInView:NO];
    [self addGestureRecognizer:GesRec];
    [GesRec release];

}


-(void)doSomething
{
    NSLog(@"doSomething");
}

回答1:

Try adding an UISwipeGestureRecognizer to the view and set cancelsTouchesInView to false so the swipe gesture is not passed through. This should let you detect left and right motion more accurately.

If this doesn't do the trick, implement your own subclass of UIGestureRecognizer and add that instead.

Edit

You add the gesture recognizer to the UITextView in your controller's viewDidLoad method.

In your delegate methods, you can't return NO in gestureRecognizer:shouldReceiveTouch: because it means the gesture recognizer won't examine the incoming touch object. In your case you want to return YES when the swipe is horizontal and NO otherwise, so vertical swipes are passed through while horizontal swipe is completed handled by you.

回答2:

No subclass needed. set textView.userInteractionEnabled to NO and than put a transparent UIView over your textView. handle touches and gestures anyway you want on that UIView and make the textView respond to these programatically.