Mac iOS 如何判断是非字符串

NSString *a=nil;

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];

[formatter setNumberStyle:NSNumberFormatterDecimalStyle];

a=@"123122..9";

//[self checkNumber:a];

NSLog(@"returned: %@####%@", [formatter numberFromString: a],a);

a=@"123122";

NSLog(@"returned: %@####%@", [formatter numberFromString: a],a);

a=@"012312.2";

NSLog(@"returned: %@####%@", [formatter numberFromString: a],a);

a=@"-12312";

NSLog(@"returned: %@####%@", [formatter numberFromString: a],a);

a=@"1dc";

NSLog(@"returned: %@####%@", [formatter numberFromString: a],a);

a=@"d2.dd";

NSLog(@"returned: %@####%@", [formatter numberFromString: a],a);