用户名为空时UITextFild 抖动

/* 用户名为空时UITextFild
抖动 */
- (void)shake{

CAKeyframeAnimation *keyAni = [CAKeyframeAnimation
animationWithKeyPath:@"position"];
[keyAni
setDuration:0.24f];

NSArray *array = [[NSArray
alloc] initWithObjects:[NSValue
valueWithCGPoint:CGPointMake(self.field.center.x,
self.field.center.y)],
[NSValue
valueWithCGPoint:CGPointMake(self.field.center.x
- 5, self.field.center.y)],
[NSValue
valueWithCGPoint:CGPointMake(self.field.center.x
+ 5, self.field.center.y)],
[NSValue
valueWithCGPoint:CGPointMake(self.field.center.x,
self.field.center.y)],nil];
[keyAni
setValues:array];
[self.field.layer
addAnimation:keyAni
forKey:@"text"];
}