UIPanGestureRecognizer中translationInView的理解

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。