textview的限制字符和回收键盘

textView的代理方法中实现下面：

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text

{
#define MY_MAX 200
    if ((textView.text.length - range.length + text.length) > MY_MAX)
    {
        NSString *substring = [text substringToIndex:MY_MAX - (textView.text.length - range.length)];
        NSMutableString *lastString = [textView.text mutableCopy];
        [lastString replaceCharactersInRange:range withString:substring];
        textView.text = [lastString copy];
        return NO;
    }else if ([@"\n" isEqualToString:text]){
        [textView resignFirstResponder];
        return NO;
    }else{
        return YES;
    }

}