Graphics Reference
In-Depth Information
To update the slider's current position, a timer is implemented whenever playback has
started. To add this, update the code for the
-togglePlayback
action, as shown in
Listing 7-4.
LISTING 7-4
Implementing a Timer
- (
IBAction
)togglePlayback:(
id
)sender;
{
if
( [movie rate] != 0.0 )
{
[movie
stop
];
[timer
invalidate
];
}
else
{
[movie play];
timer = [
NSTimer
scheduledTimerWithTimeInterval
:0.02
target
:
self
selector
:
@selector
(updateSlider:)
userInfo
:
NULL
repeats
:
YES
];
}
}
The instance variable
timer
is instantiated whenever the movie starts playing. When the
movie is stopped, we need to stop the
timer
by calling
-invalidate
on it.
The
selector
used on each tick of the timer is called
-updateSlider
. The implementa-
tion for this
selector
is shown in Listing 7-5.
LISTING 7-5
Implementing the Timer Selector
- (
void
)updateSlider:(
NSTimer
*)theTimer;
{
QTTime current = [movie currentTime];
double
value = (
double
)current.timeValue /
(
double
)movieDuration.timeValue;
[slider setDoubleValue:value];
[slider
setNeedsDisplay
];
}
This selector first obtains the current time and divides that by the movie's total time,
which is stored in the
movieDuration
instance variable. This returns a value between
0.0
