UIView的拖拽

　　做出来效果：屏幕上的一块UIView，点击后能自由移动

#import "GreenView.h"
@implementation GreenView
- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint currentP = [touch locationInView:self];
    CGPoint previousP = [touch previousLocationInView:self];
    CGFloat offsetX = currentP.x - previousP.x;
    CGFloat offsetY = currentP.y - previousP.y;
    self.transform = CGAffineTransformTranslate(self.transform, offsetX, offsetY);
}
@end