二进制表达式nsstring和id的无效操作数

Question

hi i am getting the errer invalid operends to binary expression nsstring and id even i use typecasting this is the code in which i have problem . kindly correct this code.

for (int j = 0 ; j<newarray.count ; j++){
        if(j<newarray.count){
 message = (NSString *) message + [newarray objectAtIndex:j]+ "," ;
        }
    }

Answer 1

You can not use + operator with objects, for your specific case you may replace the whole cycle with:

NSString* message = [newarray componentsJoinedByString:@","];

And FIY Objective-C does not support operator overloading at all.

Answer 2

I'm not really sure if this was your intention, but if you were trying to append new information to the string separated by commas you could go with something like this:

for (int j = 0 ; j<newarray.count ; j++){
    [message stringByAppendingString:[NSString stringWithFormat:@"%@,",[newarray objectAtIndex:j]]];
}

Additionally, your condition if(j<newarray.count) would always evaluate true in this loop, and is therefore unnecessary.

Answer 3

You should cast "[newarray objectAtIndex:j]", whose default return type is "id"

Check this

Also IIRC NSString doesn't have + operand overloaded. So maybe you should try [NSString stringWithFormat:].

Answer 4

You seem to be assuming NSString acts like std::string in C++. Try this:

NSMutableString *message = ...;
for (unsigned j = 0; j < newarray.count; j++)
{
    if (j > 0)
        [message appendString:@", "];
    [message appendString:[newarray objectAtIndex:j]];
}