creating a line between two UIlabels using the long press gesture recognizer - objective-c

Question

i am developing a ER diagram editor, i have a bunch of draggable UILabels but all of them have the same name. i want to be able to create a line between two UIlabels when both are pressed together using the long press gesture recognizer. any help will be most appreciated

Answer 1

You can create your long press gesture on the superview shared by these two labels, e.g.:
UILongPressGestureRecognizer *twoTouchLongPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self
action:#selector(handleLongPress:)];
twoTouchLongPress.numberOfTouchesRequired = 2;
[self.view addGestureRecognizer:twoTouchLongPress];
You can then write a gesture handler:
- (void)handleLongPress:(UILongPressGestureRecognizer *)gesture
{
if (gesture.state == UIGestureRecognizerStateBegan)
{
CGPoint location0 = [gesture locationOfTouch:0 inView:gesture.view];
CGPoint location1 = [gesture locationOfTouch:1 inView:gesture.view];
if ((CGRectContainsPoint(self.label0.frame, location0) && CGRectContainsPoint(self.label1.frame, location1)) ||
(CGRectContainsPoint(self.label1.frame, location0) && CGRectContainsPoint(self.label0.frame, location1)))
{
NSLog(#"success; draw your line");
}
else
{
NSLog(#"failure; don't draw your line");
}
}
}
In the updated comments, you suggest that you're creating a local UILabel variable, and then adding the resulting label to the view. That's fine, but you really want to maintain a backing model, that captures what you're doing in the view. For simplicity's sake, let me assume that you'll have array of these labels, e.g.:
#property (nonatomic, strong) NSMutableArray *labels;
Which you then initialize at some point (e.g. viewDidLoad):
self.labels = [[NSMutableArray alloc] init];
Then as you add labels to your view, add a reference to them in your array:
UILabel *label = [[UILabel alloc]initWithFrame:CGRectMake(xVal, yVal, 200.0f, 60.0f)];
label.text = sentence;
label.layer.borderColor = [UIColor blueColor].CGColor;
label.layer.borderWidth = 0.0;
label.backgroundColor = [UIColor clearColor];
label.font = [UIFont systemFontOfSize:19.0f];
[self.view addSubview:label];
[self.labels addObject:label];
Then, your gesture can do something like:
- (UILabel *)labelForLocation:(CGPoint)location
{
for (UILabel *label in self.labels)
{
if (CGRectContainsPoint(label.frame, location))
return label; // if found one, return that `UILabel`
}
return nil; // if not, return nil
}
- (void)handleLongPress:(UILongPressGestureRecognizer *)gesture
{
if (gesture.state == UIGestureRecognizerStateBegan)
{
CGPoint location0 = [gesture locationOfTouch:0 inView:gesture.view];
CGPoint location1 = [gesture locationOfTouch:1 inView:gesture.view];
UILabel *label0 = [self labelForLocation:location0];
UILabel *label1 = [self labelForLocation:location1];
if (label0 != nil && label1 != nil && label0 != label1)
{
NSLog(#"success; draw your line");
}
else
{
NSLog(#"failure; don't draw your line");
}
}
}
Frankly, I'd rather see this backed by a proper model, but that's a more complicated conversation beyond the scope of a simple Stack Overflow answer. But hopefully the above gives you an idea of what it might look like. (BTW, I just typed in the above without assistance of Xcode, so I'll apologize in advance for typos.)