原因是在破船大牛的blog上面看到了一个demo
#import <UIKit/UIKit.h>
@interface ViewController : UIViewController
@property (weak, nonatomic) IBOutlet UITextView *textView;
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@property (nonatomic, assign) CGPoint gestureStartingPoint;
@property (nonatomic, assign) CGPoint gestureStartingCenter;
@end
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
UIPanGestureRecognizer *panGes = [[UIPanGestureRecognizer alloc] initWithTarget:self
action:@selector(imagePanned:)];
[self.imageView addGestureRecognizer:panGes];
self.textView.textContainer.exclusionPaths = @[[self translatedBezierPath]];
}
- (UIBezierPath *)translatedBezierPath
{
CGRect butterflyImageRect = [self.textView convertRect:self.imageView.frame fromView:self.view];
UIBezierPath *newButterflyPath = [UIBezierPath bezierPathWithRect:butterflyImageRect];
return newButterflyPath;
}
- (void)imagePanned:(id)sender
{
if ([sender isKindOfClass:[UIPanGestureRecognizer class]]) {
UIPanGestureRecognizer *localSender = sender;
if (localSender.state == UIGestureRecognizerStateBegan) {
self.gestureStartingPoint = [localSender translationInView:self.textView];
self.gestureStartingCenter = self.imageView.center;
} else if (localSender.state == UIGestureRecognizerStateChanged) {
CGPoint currentPoint = [localSender translationInView:self.textView];
CGFloat distanceX = currentPoint.x - self.gestureStartingPoint.x;
CGFloat distanceY = currentPoint.y - self.gestureStartingPoint.y;
CGPoint newCenter = self.gestureStartingCenter;
newCenter.x += distanceX;
newCenter.y += distanceY;
self.imageView.center = newCenter;
self.textView.textContainer.exclusionPaths = @[[self translatedBezierPath]];
} else if (localSender.state == UIGestureRecognizerStateEnded) {
self.gestureStartingPoint = CGPointZero;
self.gestureStartingCenter = CGPointZero;
}
}
}
看到了translationInView方法不明白是怎么回事，就看了一下官方文档解释是：
- (CGPoint)translationInView:(UIView *)view方法的API解释如下：
The translation of the pan gesture in the coordinate system of the specified view.
Return Value
A point identifying the new location of a view in the coordinate system of its designated superview.
字面理解是：
在指定的视图坐标系统中转换(拖动？) pan gesture
返回参数：返回一个明确的新的坐标位置，在指定的父视图坐标系统中
我理解为
该方法返回在横坐标上、纵坐标上拖动了多少像素。