iOS：+ [UIView animateWithDuration：]未使用持续时间

Question

I'm trying to animate the movement of a view "falling" to the bottom of the iPad screen, with a little bounce at the end.

The bouncing effect is fine. My problem is that the "falling" animation isn't working at all like it's supposed to.

I want the animation to be linear. (I know; "falling" isn't linear, but I think it's fine in my case.) It seems to be doing ease in-ease out. The bigger problem is that I want it to be done in the duration I specify. It isn't. If distance is small, say 100 pixels, the duration computes to 0.1 seconds, and it seems to take about 0.1 seconds. But if the distance is large, say, 1000 pixels, the duration should be 1 second, but it's much longer: about 3 seconds.

Any ideas? Here's the code:

NSTimeInterval duration = (distanceToTravel / (float)1000);
NSLog(@"distance = %f, duration = %f", distanceToTravel, duration);
[UIView animateWithDuration:duration delay:0 options:(UIViewAnimationCurveLinear) animations:^ {
        wpcvc.view.center = wpcvc.startingDragLocation;
    } completion:^(BOOL finished) {
        [UIView animateWithDuration:0.2 delay:0 options:( UIViewAnimationCurveEaseOut) animations:^ {
            wpcvc.view.center = CGPointMake(wpcvc.startingDragLocation.x, wpcvc.startingDragLocation.y - 2);
        } completion:^(BOOL finished2) {
            [UIView animateWithDuration:0.2 delay:0 options:(UIViewAnimationCurveEaseIn) animations:^ {
                wpcvc.view.center = wpcvc.startingDragLocation;
            } completion:^(BOOL finished3) {
            }];
        }];
    }];

Any assistance is appreciated!

Answer 1

You shouldn't use the UIViewAnimationCurveLinear option for UIView.animateWithDuration

For linear animation you have to use the options of UIViewAnimationOptions, in your case is this UIViewAnimationOptionCurveLinear (please note the Option -difference):

[UIView animateWithDuration:duration delay:0 options:(UIViewAnimationOptionCurveLinear) animations:^ {
    wpcvc.view.center = wpcvc.startingDragLocation;
} completion:^(BOOL finished) {
    [UIView animateWithDuration:0.2 delay:0 options:( UIViewAnimationOptionCurveEaseOut) animations:^ {
        wpcvc.view.center = CGPointMake(wpcvc.startingDragLocation.x, wpcvc.startingDragLocation.y - 2);
    } completion:^(BOOL finished2) {
        [UIView animateWithDuration:0.2 delay:0 options:(UIViewAnimationOptionCurveEaseIn) animations:^ {
            wpcvc.view.center = wpcvc.startingDragLocation;
        } completion:^(BOOL finished3) {
        }];
    }];
}];

Answer 2

Just to make sure, have you turned off slow animations? The simulator has a slow animations debug setting (which I occasional accidentally toggle).

Answer 3

Are you doing this in a place that already has implicit animation, such as viewWillAppear:, viewDidAppear:, etc? If so that could be messing with the settings of your first animation as everything in there is within an animation block.

Answer 4

'wpcvc' is added to no superview? (or super-superview so?)

[(superview) addSubview:wpcvc];
[UIView animateWithDuration:...

It is necessary for target view to be added to some superview beforehand.