Animating GMSMarker in a circular path

问题

I understand how to normally animation other CALayers in a circular path based on this SO question: iPhone - How to make a circle path for a CAKeyframeAnimation?

However, the GMSMarkerLayer is a special subclass of CALayers that does not seem to respond to the "position" keypath (following instructions in that link does nothing that I can visibly see) but instead will respond to the "latitude" and "longitude" keypaths instead.

Here's the code that I've tried:

CAKeyframeAnimation *circlePathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
CGMutablePathRef circularPath = CGPathCreateMutable();
CGRect pathRect = CGRectMake(marker.position.latitude, marker.position.longitude, 0.001, 0.001);
CGPathAddEllipseInRect(circularPath, NULL, pathRect);
circlePathAnimation.path = circularPath;
circlePathAnimation.duration = 1.0f;
circlePathAnimation.repeatCount = HUGE_VALF;

[marker.layer addAnimation:circlePathAnimation forKey:[NSString stringWithFormat:@"circular-%@", marker.description]];
CGPathRelease(circularPath);

Since the keyframe animation will use the "position" keypath, how can I convert that into 2 separate keypaths (latitude and longitude) so I can animate the marker in a circle on the map?

Any help is greatly appreciated.

回答1:

As currently I cannot use the "position" keypath for animating, I ended up animating it using the "latitude" and "longitude" keypaths separately.

First calculate the points and add them to 2 separate arrays, one for latitude value (y) and one for longitude (x) and then use the values property in CAKeyFrameAnimation to animate. Create 2 CAKeyFrameAnimation objects (1 for each axis) and group them together using CAAnimationGroup and animate them together to form a circle.

In my equation I vary the length of the radius on each axis so that I can also generate an oval path.

    NSMutableArray *latitudes = [NSMutableArray arrayWithCapacity:21];
    NSMutableArray *longitudes = [NSMutableArray arrayWithCapacity:21];
    for (int i = 0; i <= 20; i++) {
        CGFloat radians = (float)i * ((2.0f * M_PI) / 20.0f);

        // Calculate the x,y coordinate using the angle
        CGFloat x = hDist * cosf(radians);
        CGFloat y = vDist * sinf(radians);

        // Calculate the real lat and lon using the
        // current lat and lon as center points.
        y = marker.position.latitude + y;
        x = marker.position.longitude + x;


        [longitudes addObject:[NSNumber numberWithFloat:x]];
        [latitudes addObject:[NSNumber numberWithFloat:y]];
    }

    CAKeyframeAnimation *horizontalAnimation = [CAKeyframeAnimation animationWithKeyPath:@"longitude"];
    horizontalAnimation.values = longitudes;
    horizontalAnimation.duration = duration;

    CAKeyframeAnimation *verticleAnimation = [CAKeyframeAnimation animationWithKeyPath:@"latitude"];
    verticleAnimation.values = latitudes;
    verticleAnimation.duration = duration;

    CAAnimationGroup *group = [[CAAnimationGroup alloc] init];
    group.animations = @[horizontalAnimation, verticleAnimation];
    group.duration = duration;
    group.repeatCount = HUGE_VALF;
    [marker.layer addAnimation:group forKey:[NSString stringWithFormat:@"circular-%@",marker.description]];

来源：https://stackoverflow.com/questions/19227017/animating-gmsmarker-in-a-circular-path