Why is (self.window) in the following code a condition? - ios

Question

Why is (self.window) in the following code a condition?
-(void)beginRefreshing {
[UIView animateWithDuration:MJRefreshFastAnimationDuration
animations:^{
self.alpha = 1.0;
}];
self.pullingPercent = 1.0;
if (self.window) {
self.state = MJRefreshStateRefreshing;
} else {
self.state = MJRefreshStateWillRefresh;
[self setNeedsDisplay];
}
}

Answer 1

In this case:
if (self.window) {
which is a short version of
if (self.window != nil) {
is a test whether the view (UIView instance) is in the view hierarchy of any window, that is, whether the view is displayed on the screen.

Answer 2

Certain variables are boolean meaning they can either be equal to true or false. Others can have a wide range of values. for example off you want to do something if an Integer is equal to 5 you can write:
if (myInt == 5) {
//do something
}
If your variable is a Boolean there are only two options so we can write is shorter:
if (myBoolean) {
//case where myBoolean = true
} else {
//case where myBoolean = false
}
In your particular example, self.window evaluates to a Boolean in the following manner: either self.windows exists in the view hierarchy or not (self.windows == true) or it do not (self.windows == false).

Answer 3

I've decided to expand my comment to an answer for future reference.
It's actually a side effect, AFAIK. Because false is defined as 0, and true is defined as anything different than 0. A valid objects address is non-zero so it is treated as true, whereas, thanks to ARC, nil == 0. You can check this by printing this NSLog(#"%p", nil). Bear in mind, that for integers, this means that a negative value, also evaluates to true
It is also worth noting, that because the underlying storage for a boolean is rarely one-bit it may not always be true that when someBool == true, then someBool == 1. This means that taking such a shortcut :
- (NSInteger)increment:(NSInteger)toIncrement ifTrue:(BOOL)condition {
return toIncrement + condition;
}
may not always lead to toIncrement being incremented by 1. The code is valid, becasue a BOOL will get promoted to integer automatically.
This is of course somwhat of an edge case, but still possible.