防止视图被拖出屏幕

Question

我需要防止视图被拖过屏幕边缘。换句话说，当视图的边缘到达屏幕的边缘时，视图无法在该方向上继续移动。

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    UITouch *touchInfo = [touches anyObject]; 

    if (touchInfo.view == self) 
    { 
     CGPoint touchStart = [touchInfo previousLocationInView:self]; 
     CGPoint touchEnd = [touchInfo locationInView:self]; 
     CGFloat xDifference = touchEnd.x - touchStart.x; 
     CGFloat yDifference = touchEnd.y - touchStart.y; 

     CGPoint newCenter = CGPointMake(self.center.x + xDifference, self.center.y + yDifference); 

     [self setCenter:newCenter]; 
    } 
} 

Answer 1

CGRect  bounds = self.bounds; 
CGRect  limit = CGRectInset(self.superview.bounds, bounds.size.width/2., bounds.size.height/2.); 

...

newCenter.x = fmaxf(limit.origin.x, fminf(limit.origin.x + limit.size.width, newCenter.x)); 
newCenter.y = fmaxf(limit.origin.y, fminf(limit.origin.y + limit.size.height, newCenter.y)); 

Answer 2

加边检查，这样

CGRect superBounds = self.superView.bounds; 

//check if this is past the right edge 
if (newCenter.x + self.bounds.size.width/2 > superBounds.origin.x) 
{ 
    newCenter.x = superBounds.size.width - self.bounds.size.width/2; 
} 

//Do the same thing for the top, bottom, and left edges 
//... 

Answer 3

你试过CGRectContainsRect？这里是文档：https://developer.apple.com/library/ios/documentation/graphicsimaging/reference/CGGeometry/Reference/reference.html#//apple_ref/c/func/CGRectContainsRect

if (CGRectContainsRect(superViewBounds,subViewBounds)){ 
//within the screen bounds 
} else { 
//_not_ within the screen bounds 
}