From an array, I want to make a new mutable array holding all the items that meet a certain criteria. That's not the problem. The problem is checking if the array is empty.
if (!theDates]) {/*do something*/}
it comes back positive regardless, because the mutable array was created. But
if (![theDates objectAtIndex:0])
{
/* nothing got added to the array, so account for that */
}
else
{
/* do something with the array */
}
It crashes.
This crashes because although you have allocated your array, it's still empty. The line [theDates objectAtIndex:0] is trying to access the first object of an array, and due your array has none yet, it will crash.
To check the integrity of your array, just do this:
if (theDates.count > 0)
{
//Do something
id object = theDates[0]; //this for sure won't crash
}
if (theDates.count) {
> 0 for this check. Of course it's not wrong but it's not needed either.> 0 in my codes, you write two more characters but you gain in legibility. It's a matter of opinion in fact, both will workUse [theDates count] > 0. You're accessing a possibly non-existent element, so it will crash when it's empty.
Or you could use the lastObject method which will return nil if the array is empty
if (![theDates lastObject]) { do something }
if( (theDates!=nil) && (theDates.count > 0))
{
//We have and existing array and something in there..
}
if (theDates != nil){
if (theDates.count > 0){
'do something'
}
}
This should check null array then check empty array which prevents nullpointerexception arises
if statement. And it is standard convention to use nil, not null when dealing with Cocoa/Cocoa-touch object pointers.
This will work fine..
if (!URarray || !URarray.count){
// write code here
}
