textfield 拼音高亮限制字数

UITextRange *selectedRange = [textField markedTextRange];
    //获取高亮部分
    UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
    //没有高亮选择的字，则对已输入的文字进行字数统计和限制
    if(!position) {
        if (textField.text.length >= 10) {
            NSRange rangeRange = [textField.text rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, 10)];
            textField.text = [textField.text substringWithRange:rangeRange];
            
        }
    }