NSString from NSArray

问题

I am trying to create a String from Array.But, there is condition to how it should be generated, as explained below.

NSArray *array=[NSArray arrayWithObjects:@"Hello",@"World",nil];
[array componentsJoinedByString:@","];

This will output: Hello,World.

But, if first Item is Empty,then is there way to receive the only second one.

1. Hello , @"" => Hello
2. @"" , World => World
3. Hello , World => Hello,World

回答1:

Another way to do this is to grab a mutable copy of the array and just remove non valid objects. Something like this perhaps:

NSMutableArray *array = [[NSArray arrayWithObjects:@"",@"World",nil] mutableCopy];
[array removeObject:@""]; // Remove empty strings
[array removeObject:[NSNull null]]; // Or nulls maybe

NSLog(@"%@", [array componentsJoinedByString:@","]);

回答2:

You cannot store nil values in NSArray^*, so the answer is "no". You need to iterate the array yourself, keeping track of whether you need to add a comma or not.

NSMutableString *res = [NSMutableString string];
BOOL first = YES;
for(id item in array) {
    if (id == [NSNull null]) continue;
    // You can optionally check for item to be an empty string here
    if (!first) {
        [res appendString:@", "];
    } else {
        first = NO;
    }
    [res appendFormat:@"%@", item];
}

---

^*nil values in NS collections are represented with NSNull objects.

来源：https://stackoverflow.com/questions/14366431/nsstring-from-nsarray