CODEWITHSUNDEEP
iosiphoneuikituigesturerecognizeruipangesturerecognizer
gran33
gran33

Reputation: 12981

Velocity issues in setTranslation:inView:

I's using this method:

- (void)setTranslation:(CGPoint)translation inView:(UIView *)view

From UIPanGestureRecognizer class, and I don't understand the velocity discussions around that.

Appel's documentation says:

Sets the translation value in the coordinate system of the specified view. Changing the translation value resets the velocity of the pan.

What's that exactly mean? What is "reset velocity of the pan"?

Any help will be appreciated.. Thanks in advance!

--EDIT

See this code:

if (recognizer.state == UIGestureRecognizerStateChanged) {
        CGPoint translation = [recognizer translationInView:self.cardsScrollView];        

        recognizer.view.center = CGPointMake(recognizer.view.center.x, recognizer.view.center.y + translation.y);

        [recognizer setTranslation:CGPointMake(0, 0) inView:recognizer.view];
...
}

Upvotes: 3

Views: 562

Answers (1)

Jernej Strasner
Jernej Strasner

Reputation: 4620

What it means is that if you're in the middle of the panning gesture (you're dragging something) and you call setTranslation:inView: on that gesture, it's velocity is going to be reset to 0; A pan gesture not only gives you the translation but also the velocity of the gesture (how fast you're dragging) in units per second (points per second in this case). You can access the velocity by calling velocityInView:. If you don't use the velocity then don't worry about it, otherwise keep the above in mind.

UPDATE:

I'm guessing you're trying to move the view as you drag it. I would do it slightly differently.

if (recognizer.state == UIGestureRecognizerStateBegan) {
    CGAffineTransform transform = recognizer.view.transform;
    [recognizer setTranslation:CGPointMake(transform.tx, transform.ty) inView:self];
} else if (recognizer.state == UIGestureRecognizerStateChanged) {
    CGPoint translation = [recognizer translationInView:self.cardsScrollView];
    recognizer.view.transform = CGAffineTransformMakeTranslation(translation.x, translation.y);
}

The thing to keep in mind is that self.cardsScrollView should be the superview of the view you're trying to move.

Upvotes: 1

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