Graphics Programs Reference
In-Depth Information
Detecting Taps with UITapGestureRecognizer
The first
UIGestureRecognizer
subclass you will use is
UITapGestureRecog-
nizer
. When the user taps a line in
TouchTracker
, you will present a menu that allows
In the first part of this section, we are going to recognize a tap, determine which line is
close to where the tap occurred, store a reference to that line, and change that line's color to
green so that the user knows it has been selected.
In
TouchDrawView.m
, edit the
initWithFrame:
method to create an instance of
UITapGestureRecognizer
and attach it to the
TouchDrawView
being initialized.
- (id)initWithFrame:(CGRect)r
{
self = [super initWithFrame:r];
if (self) {
linesInProcess = [[NSMutableDictionary alloc] init];
completeLines = [[NSMutableArray alloc] init];
[self setBackgroundColor:[UIColor whiteColor]];
[self setMultipleTouchEnabled:YES];
UITapGestureRecognizer *tapRecognizer =
[[UITapGestureRecognizer alloc] initWithTarget:self
action:@selector(tap:)];
[self addGestureRecognizer:tapRecognizer];
}
return self;
}
Now whenever a tap occurs on this
TouchDrawView
, the
UITapGestureRecog-
nizer
will send it the message
tap:
. In
TouchDrawView.m
, implement the
tap:
method. For now, just have it log something to the console.
- (void)tap:(UIGestureRecognizer *)gr
{
NSLog(@"Recognized tap");
}
Build and run the application and then tap on the screen. You should notice two things: the
console reports that a tap was recognized, and a dot is drawn on the view. That dot is a very
short line and a bug. In this application, we don't want anything drawn in response to a tap.
Add the following code to
tap:
to remove any lines in process and redisplay the view.
