iPhone - 慣性拖動

Question

我有一個對象，用戶必須拖動屏幕。這是一個普通的UIImageView。目前，圖像可以被拖動，但是當您釋放圖像時，它會停止在您的手指擡起圖像的位置。我想要創造的勢頭，所以我可以給圖像一個衝動，它會滾動，直到它彈起屏幕邊緣。

我不想要像添加物理庫和類似的東西非常複雜。我想盡可能保持最小。

我該怎麼做？你們能指點我一些教程還是朝着正確的方向發展？

謝謝。

Answer 1

好一個這樣做不使用任何物理庫的方式是這樣的：

首先在你的類創建4個實例變量是這樣的：

CFTimeInterval startTime; 
CGPoint startPoint; 
CGPoint oldPoint; 
BOOL imageViewTouched; 

比你- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event方法有這樣的代碼：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    UITouch *touch = [[event allTouched] anyObject]; 
    // Test to see if the touched view is your image view. If not just return. 
    if (touch.view != <#yourImageView#>) { 
     return; 
    } 

    startPoint = [touch locationInView:self.view]; 
    oldPoint = startPoint; 
    startTime = CACurrentMediaTime(); 
    imageViewTouched = YES; 
} 

對於- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event做到這一點：

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    // Fingers were moved on the screen but your image view was not touched in the beginning 
    if (!imageViewTouched) { 
     return; 
    } 

    UITouch *touch = [[event allTouches] anyObject]; 
    CGPoint newPoint = [touch locationInView:self.view]; 

    <#yourImageView#>.frame = CGRectOffset(<#yourImageView#>.frame, newPoint.x - oldPoint.x, newPoint.y - oldPoint.y); 
    oldPoint = newPoint; 
} 

現在對於- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event試試這個：

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    // Fingers were removed from the screen but your image view was not touched in the beginning 
    if (!imageViewTouched) { 
     return; 
    } 

    imageViewTouched = NO; 

    UITouch *touch = [[event allTouches] anyObject]; 
    CGPoint endPoint = [touch locationInView:self.view]; 
    CFTimeInterval endTime = CACurrentMediaTime(); 

    CFTimeInterval timeDifference = endTime - startTime; 

    // You may play with this value until you get your desired effect 
    CGFloat maxSpeed = 80; 

    CGFloat deltaX = 0; 
    CGFloat deltaY = 0; 

    if (timeDifference < 0.35) { 
     deltaX = (endPoint.x - startPoint.x)/(timeDifference * 10); 
     deltaY = (endPoint.y - startPoint.y)/(timeDifference * 10); 
    } 

    if  (deltaX > maxSpeed)   { deltaX = maxSpeed; } 
    else if (deltaX < -maxSpeed)  { deltaX = -maxSpeed; } 
    else if (deltaX > -5 && deltaX < 5) { deltaX = 0; } 

    if  (deltaY > maxSpeed)   { deltaY = maxSpeed; } 
    else if (deltaY < -maxSpeed)  { deltaY = -maxSpeed; } 
    else if (deltaY > -5 && deltaY < 5) { deltaY = 0; } 

    [UIView begginAnimations:nil context:nil]; 
    [UIView setAnimationDuration:0.5f]; 
    [UIView setAnimationCurve:UIViewAnimationCurveEaseOut]; 

    <#yourImageView#>.frame = CGRectOffset(<#yourImageView#>.frame, deltaX, deltaY); 

    [UIView commitAnimations]; 
} 

請讓我知道，如果這是有道理的和/或你的作品。乾杯!