UITextView text length limitation

iOS8 以上键盘的自动联想功能使UITextView的长度限制产生一些bug

• 再谈multistage text input（中文输入法）下UITextView的内容长度限制
• textViewDidChange: crashes in iOS 7

#define textLimitLength 50
#pragma mark - UITextViewDelegate
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    if (textView.text.length >= textLimitLength && text.length > range.length) {
        return NO;
    }
    return YES;
}

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