How to keep the position unchanged in ios but only the width changes.

Question

    CABasicAnimation *leftboundsanimation = [CABasicAnimation animationWithKeyPath:@"bounds.size.width"];
    leftboundsanimation.fromValue = [NSNumber numberWithFloat:1];
    //[NSValue valueWithCGSize:CGSizeMake(1, 20)];
    leftboundsanimation.toValue   = [NSNumber numberWithFloat:animationrectwidth/2-0.5];

// [NSValue valueWithCGSize:CGSizeMake(animationrectwidth/2-0.5, 20)];

    leftboundsanimation.removedOnCompletion  =   NO;
    leftboundsanimation.fillMode =   kCAFillModeForwards;
    leftboundsanimation.duration  = 1.3;
    leftboundsanimation.beginTime   =   2.7;

Answer 1

CABasicAnimation version:

How to change the width of a CALayer with animation from left to right?

CGRect bounds = self.view.bounds;
CALayer *layer = self.view.layer;
layer.position = CGPointMake(0, 0);
layer.anchorPoint = CGPointMake(0, 0);

CABasicAnimation *leftBoundsAnimation = [CABasicAnimation animationWithKeyPath:@"bounds"];
leftBoundsAnimation.duration = 1.3;
leftBoundsAnimation.toValue = [NSValue valueWithCGRect:bounds];
bounds.size.width = 0;
leftBoundsAnimation.fromValue = [NSValue valueWithCGRect:bounds];

[layer addAnimation:leftBoundsAnimation forKey:@"leftBoundsAnimation"];

UIView其实有直接提供动画方法的。
改变一个view的宽度：

CGRect frame = self.view.frame;
frame.size.width = 300;
[UIView animateWithDuration:1.3 animations:^{
    self.view.frame = frame;
}];