Delay before apply object changes (similar like setNeedsDisplay) - ios

Question

I have object with properties and when I change some of properties, I do a lot of calculations. If I change one property, then another, calculations execute 2 times. I want do all calculations 1 time. I see 3 solution:
Make method commit. But I don't wanna do excess methods.
Make method for change all properties. The same cause why I don't wanna do this. And what to do if I will have much more properties in future.
Make delay after delay commit changes. I really do not know what consequences this may turn into. Something like this:
.
#interface TestObject : NSObject
#property (nonatomic, assign) float x;
#property (nonatomic, assign) float y;
#end
#implementation TestObject
{
BOOL flag;
}
- (id)init
{
self = [super init];
if(self){
flag = NO;
}
return self;
}
- (void)setX:(float)x
{
_x = x;
[self delayCommit];
}
- (void)setY:(float)y
{
_y = y;
[self delayCommit];
}
- (void)delayCommit
{
if(flag == NO){
flag = YES;
[self performSelector:#selector(commit) withObject:nil afterDelay:0];
}
}
- (void)commit
{
flag = NO;
NSLog(#"Do a lot of calculations....");
}
#end
Is third solution good practice? I want simple interface, I don't want excess methods.

Answer 1

If you really want a behavior like that, you should then have a timer that every N seconds, checks if any of the properties are changed, and does the computations. Something like:
- (void)setX:(float)x
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_semaphore_wait(_mySem, DISPATCH_TIME_FOREVER);
_x = x;
flag = YES;
dispatch_semaphore_signal(_mySem);
});
}
- (void)setY:(float)y
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_semaphore_wait(_mySem, DISPATCH_TIME_FOREVER);
_y = y;
flag = YES;
dispatch_semaphore_signal(_mySem);
});
}
- (void)updateCycle
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
dispatch_semaphore_wait(_mySem, DISPATCH_TIME_FOREVER);
if(flag){
flag = NO;
NSLog(#"Do a lot of calculations....");
}
dispatch_semaphore_signal(_mySem);
});
}
In your init method you would have to initialise the timer and the semaphore with
_mySem = dispatch_semaphore_create(1);
[NSTimer scheduledTimerWithTimeInterval:N
target:self
selector:#selector(updateCycle)
userInfo:nil
repeats:YES];
The way to use it would then just be:
[object setX:4.5f];
[object setY:0.3f];

Answer 2

Depending on how many properties you have, this may work for you instead:
- (void)setX:(float)x y:(float)y
{
_x = x;
_y = y;
[self commit];
}
Here, you set more than one property with one method call. You know you have all the values you need, so you can call commit directly.

Answer 3

I would suggest you not to try to be too fancy with delayed commits (unless you really have to) and to use commit as a separate call and perform your long calculation in a separate thread, e.g.:
- (void)setX:(float)x
{
_x = x;
}
- (void)setY:(float)y
{
_y = y;
}
- (void)commitChanges
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// ... Long calculations go here ...
dispatch_async(dispatch_get_main_queue(), ^{
// ... Once you done with your long calculation, put your UI code here
// ... (e.g. display results of your calculation in text box)
});
});
}
then from your main code will look like:
[obj setX:123.0f];
[obj setY:345.0f];
[obj commitChanges];