经常有需求 要判断不能为空，后台老是鄙视不做非空判断的前端 ，木办法 只能写一个。
第一种想法：我不就是判断 是不是nil就可以了么。结果发现太天真，用户可以输入空格。
对于这种蛋疼的用户，只能采取蛋疼的方法：
-(Bool) isEmpty:(NSString *) str {
if (!str) {
return true;
} else {
//A character set containing only the whitespace characters space (U+0020) and tab (U+0009) and the newline and nextline characters (U+000A–U+000D, U+0085).
NSCharacterSet *set = [NSCharacterSet whitespaceAndNewlineCharacterSet];
//Returns a new string made by removing from both ends of the receiver characters contained in a given character set.
NSString *trimedString = [str stringByTrimmingCharactersInSet:set];
if ([trimedString length] == 0) {
return true;
} else {
return false;
}
}
}