How restrict movement in animateWithDuration - iphone

Question

I'm creating app where UILabel object will move over the screen. My question is how I can restrict the label to go over the specific border. For example if the label have a message, I want have the whole message visible, not just the first part of it.
This is the code:
#define kHeight 320.0
#define kWidth 400.0
#define kTransitionDuration 1.50
#define kTopPlacement 80.0
- (void)myMover {
for (UIView *view in self.view.subviews) {
if( [view isKindOfClass:[UILabel class]]){
[UIView animateWithDuration:4.0 animations:^{
//set the point from where the move will start
[self setRandomLocationForLabel:view];
}];
}
}
}
- (void) setRandomLocationForView:(UIView *)view
{
[view sizeToFit];
CGRect messageViewBounds = CGRectMake(round((self.view.bounds.size.width - kWidth) / 2.0),
200, kWidth, kHeight);
CGRect newFrame = CGRectMake( 0, 300, 100 , 20 );
while (view.frame.size.width > kWidth) {
newFrame.size.width /= 2;
newFrame.size.height /= 2;
}
view.frame = newFrame;
CGFloat x = (CGFloat) (arc4random() % (int) messageViewBounds.size.width + view.frame.size.width/2);
CGFloat y = (CGFloat) (arc4random() % (int) messageViewBounds.size.height + view.frame.size.height/2);
view.center = CGPointMake (x,y);
}
Thank you for any advice!

Answer 1

Since you have the view you know its size. By knowing the width you know how far you need to position the center of the view from left or right (half the width). By knowing the height you know how from top or bottom (half the height).
Now you can calculate the rectangle that contains only the valid center points for that view by taking the full view and create an inset rectangle with half the width of your view subtracted on both left and right and half the height of your view subtracted on both top and bottom.
CGSize viewSize = view.bounds.size; // The view you are positioning
CGRect rectOfValidCenters = CGRectInset(self.view.bounds, // The view you are placing it in
viewSize.width/2.0, // subtract the width/2 from left and right
viewSize.height/2.0); // subtract the height/2 form top and bottom
CGFloat randomX = // generate random value from 0.0 to 1.0
CGFloat randomY = // generate random value from 0.0 to 1.0
// Random valid center point is:
// ( minX + randomX * width , minY + randomY * height)
//
// if x and y are zero then the view's center will be in the upper left
// of the rect of valid centers (making its upper left corner be in the
// top left of the view it's placed in).
// if x and y are one then the view's center will be in the lower right
// of the rect of valid centers (making its lower right corner be in the
// lower right of the view it's placed in).
CGPoint randomValidPoint = CGPointMake(CGRectGetMinX(rectOfValidCenters) + randomX * CGRectGetWidth(rectOfValidCenters),
CGRectGetMinY(rectOfValidCenters) + randomY * CGRectGetHeight(rectOfValidCenters));
view.center = randomValidPoint;

Answer 2

My question is how I can restrict the label to go over the specific border. For example if the label have a message, I want have the whole message visible, not just the first part of it.
You will need to take into account the length/width and height of the label when determining the random position it should land on. As such, your random selection should land in the area of
CGSize labelSize = [messageString sizeWithFont:messageString.font
constrainedToSize:maximumLabelSize
lineBreakMode:messageString.lineBreakMode];
CGFloat minX = 0;
CGFloat minY = 0;
CGFloat maxX = self.view.frame.size.width - labelSize.width;
CGFloat maxY = self.view.frame.size.height - labelSize.height;
// Use minX/Y and maxX/Y in your random co-ordinate algorithm