ios 判断空字符串

- (BOOL) isBlankString:(NSString *)string {

if (string == nil || string == NULL) {

return YES;

}

if ([string isKindOfClass:[NSNull class]]) {

return YES;

}

if ([[string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] length]==0) {

return YES;

}

return NO;

}