allowableMovement似乎被忽略

Question

我的UILongPressGestureRecognizer中的allowableMovement屬性似乎被忽略。我使用Single View Application模板創建了一個新項目（Xcode 4.5.1，iOS 6），並在視圖中添加了長按手勢識別器。有一個連接線和一個動作。下面是操作方法的代碼：

- (IBAction)longPress:(UILongPressGestureRecognizer *)sender 
{  
    if (sender.state == UIGestureRecognizerStatePossible) NSLog(@"possible"); 
    if (sender.state == UIGestureRecognizerStateBegan)  NSLog(@"began"); 
    if (sender.state == UIGestureRecognizerStateChanged) NSLog(@"changed");  
    if (sender.state == UIGestureRecognizerStateRecognized) NSLog(@"recognized");  
    if (sender.state == UIGestureRecognizerStateCancelled) NSLog(@"cancelled"); 
    if (sender.state == UIGestureRecognizerStateFailed)  NSLog(@"failed"); 

    CGPoint locationInView = [sender locationInView:self.view]; 

    NSLog(@"long press: allowableMovement= %f, x= %f, y= %f", sender.allowableMovement, locationInView.x, locationInView.y); 
} 

如果我按下足夠長的時間放手我在日誌中得到這樣的：

2012-10-30 20:24:41.449 Long Press[1078:907] began 
2012-10-30 20:24:41.455 Long Press[1078:907] long press: allowableMovement= 10.000000, x= 210.500000, y= 99.500000 
2012-10-30 20:24:42.880 Long Press[1078:907] recognized 
2012-10-30 20:24:42.882 Long Press[1078:907] long press: allowableMovement= 10.000000, x= 208.500000, y= 96.000000 

這是我所期望的那樣。

但無論我將allowableMovement設置爲（正面，負面，大，小），一旦狀態爲UIGestureRecognizerStateBegan，我就可以將手指拖到屏幕上。狀態更改爲UIGestureRecognizerStateChanged，並且頻繁更新，並且locationInView繼續準確跟蹤。當我放手的時候，我得到了UIGestureRecognizerStateRecognized狀態，並且最終輸出到了日誌中。

該類參考指出，如果移動超過allowableMovement，識別器將失敗。爲什麼allowableMovement屬性似乎被忽略？

Answer 1

allowableMovement屬性不是關於手勢開始後您可以拖動多遠。這是關於手勢開始前你能移動多遠。

從類參考：

手勢開始（UIGestureRecognizerStateBegan）當已經按下的指定時段內（minimumPressDuration）容許手指（numberOfTouchesRequired）的數量和接觸不移動超出容許範圍運動（allowableMovement）。

當設置minimumPressDuration的東西高像3秒allowableMovement的東西等低1個像素，這變得明顯。如果你的手指在所有手勢上滾動，手勢將不會開始。但是，如果將allowableMovement設置爲100，則手指可以轉動很多，手勢將開始。

這樣就像其他屬性一樣。他們都是關於手勢開始所需的。

Answer 2

我以爲allowableMovement有這個目的。我做了一個小的子類來實現allowableMovementAfterBegan的「預期」行爲。

#import <UIKit/UIKit.h> 
#import <UIKit/UIGestureRecognizerSubclass.h> 

@interface TDMLongPressGestureRecognizer : UILongPressGestureRecognizer 
@property (nonatomic, assign) CGFloat allowableMovementAfterBegan; 
@end 

@implementation TDMLongPressGestureRecognizer 
{ 
    CGPoint initialPoint; 
} 

- (instancetype)initWithTarget:(id)target action:(SEL)action 
{ 
    self = [super initWithTarget:target action:action]; 
    if (self) { 
     // Use default value for allowableMovement before touches begin 
     _allowableMovementAfterBegan = self.allowableMovement; 
    } 
    return self; 
} 

- (void)reset 
{ 
    [super reset];  
    initialPoint = CGPointZero; 
} 

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [super touchesBegan:touches withEvent:event]; 
    initialPoint = [self locationInView:self.view]; 
} 

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [super touchesMoved:touches withEvent:event]; 

    if (!CGPointEqualToPoint(initialPoint, CGPointZero)) 
    { 
     CGPoint currentPoint = [self locationInView:self.view]; 

     CGFloat distance = hypot(initialPoint.x - currentPoint.x, initialPoint.y - currentPoint.y); 
     if (distance > self.allowableMovementAfterBegan) 
      self.state = UIGestureRecognizerStateFailed; 
     } 
    } 
}