UITextView、UITextField限制长度

需求：UITextView、UITextField输入的文字限制长度，但删除部分文字之后能继续输入文字

UITextView利用代理

    _planTextView = [[UITextView alloc]init];
    _planTextView.delegate =  self ;

      - (void)textViewDidChange:(UITextView *)textView
    {
        if (textView.text.length >= 50) {
            textView.text = [textView.text substringToIndex:50];
          }
    }

UITextField利用监听的方式

    _planNameView = [[UITextField alloc]init];
    [_planNameView addTarget:self action:@selector(textFieldDidChange:) forControlEvents:UIControlEventEditingChanged];

    - (void)textFieldDidChange:(UITextField *)textField
    {
         if (textField.text.length > 100) {
            textField.text = [textField.text substringToIndex:100];
            }
    }