整理了一份Demo，因为每个项目具体的需求不一样，我只把基本的功能整理出来了
Demo放在GitHub上
项目中要实现填空题的作答功能，比如诗词填空：床前明月光，___________。举头望明月，________。要求只能编辑横线部分。
首先想到的是强大的YYKit，先在网上找了找，发现有一种方案是用label 加textfield的这种富文本编辑的方式实现的，虽然大体符合需求，但是排版会比较难看。
最后决定用YYTextView去实现，原理就是根据正则匹配题干和下划线，整个题目会被填空部分分割成几块，把各个分块binding，然后控制光标位置，只让光标落在下划线上。

创建题目：

   NSMutableAttributedString *text = [[NSMutableAttributedString alloc] initWithString:@"#（填空题）枯藤老树昏鸦,#      #,古道西风瘦马。#      #,断肠人在天涯。# "];
   text.yy_font = [UIFont systemFontOfSize:17];
   text.yy_lineSpacing = 5;
   text.yy_color = [UIColor blackColor];
   YYTextView *textView = [YYTextView new];
   textView.textParser = [YYTextEditBindingParser new];
   textView.attributedText = text;
   textView.frame = CGRectMake(5, 100, CGRectGetWidth(self.view.frame)-10, 200);
   textView.textContainerInset = UIEdgeInsetsMake(10, 10, 10, 10);
   textView.delegate = self;
   if (kiOS7Later) {
       textView.keyboardDismissMode = UIScrollViewKeyboardDismissModeInteractive;
   }
   textView.scrollIndicatorInsets = textView.contentInset;
   [self.view addSubview:textView];
   self.textView = textView;

在代理方法里面控制光标位置

#pragma mark YYTextViewDelegate
- (BOOL)textViewShouldBeginEditing:(YYTextView *)textView{
    
    if (textView.selectedRange.location==0 || textView.selectedRange.location >= textView.text.length) {
        return NO;
    }else{
        return [self controllCursorRangeForTextView:textView];
    }
}
- (void)textViewDidChangeSelection:(YYTextView *)textView{
    if (textView.selectedRange.location==0 || textView.selectedRange.location >= textView.text.length) {
        [textView endEditing:YES];
    }else {
        [self controllCursorRangeForTextView:textView];
    }
    
}

控制光标

- (BOOL)controllCursorRangeForTextView:(YYTextView *)textView{
    YYTextEditBindingParser *textParser = textView.textParser;
    for (NSString *rangeStr in textParser.gapRangeArr) {
        NSRange range = NSRangeFromString(rangeStr);
        if (textView.selectedRange.location >= range.location && textView.selectedRange.location < range.location + 3) {
            textView.selectedRange = NSMakeRange(range.location + 3,0);
            return YES;
        }else if(textView.selectedRange.location > (range.location + range.length -3)&&textView.selectedRange.location <= (range.location + range.length)){
            textView.selectedRange = NSMakeRange(range.location + range.length - 3,0);
            return YES;
        }
    }
    return YES;
}

为了不让删除binding的字符串我在YYtextView里面加了个代理方法，在我这里实现一下：

- (BOOL)textViewShouldDeleteBinding:(YYTextView *)textView{
    return NO;
}

YYTextEditBindingParser这个类用于binding和对输入内容加下划线,有个属性gapRangeArr用来保存填空部分的range

@interface YYTextEditBindingParser :NSObject <YYTextParser>
@property (nonatomic, strong) NSRegularExpression *regex;
@property (nonatomic, strong) NSRegularExpression *gapRegex;
@property(nonatomic, strong)NSArray <NSString *>*gapRangeArr;

@end

@implementation YYTextEditBindingParser

- (instancetype)init {
    self = [super init];
    NSString *pattern1 = @"#([^#]*)#";
    self.regex = [[NSRegularExpression alloc] initWithPattern:pattern1 options:kNilOptions error:nil];
    NSString *pattern2 = @"\\s{3}([^\\s{3}]*)\\s{3}";
    self.gapRegex = [[NSRegularExpression alloc] initWithPattern:pattern2 options:kNilOptions error:nil];
    return self;
}
- (NSRange)_replaceTextInRange:(NSRange)range withLength:(NSUInteger)length selectedRange:(NSRange)selectedRange {
    // no change
    if (range.length == length) return selectedRange;
    // right
    if (range.location >= selectedRange.location + selectedRange.length) return selectedRange;
    // left
    if (selectedRange.location >= range.location + range.length) {
        selectedRange.location = selectedRange.location + length - range.length;
        return selectedRange;
    }
    // same
    if (NSEqualRanges(range, selectedRange)) {
        selectedRange.length = length;
        return selectedRange;
    }
    // one edge same
    if ((range.location == selectedRange.location && range.length < selectedRange.length) ||
        (range.location + range.length == selectedRange.location + selectedRange.length && range.length < selectedRange.length)) {
        selectedRange.length = selectedRange.length + length - range.length;
        return selectedRange;
    }
    selectedRange.location = range.location + length;
    selectedRange.length = 0;
    return selectedRange;
}
- (BOOL)parseText:(NSMutableAttributedString *)text selectedRange:(NSRangePointer)range {
    __block BOOL changed = NO;
    NSArray *matches = [_regex matchesInString:text.string options:kNilOptions range:NSMakeRange(0, text.length)];
    NSRange selectedRange = range ? *range : NSMakeRange(0, 0);
    NSUInteger cutLength = 0;
    for (NSUInteger i = 0, max = matches.count; i < max; i++) {
        NSTextCheckingResult *one = matches[i];
        NSRange oneRange = one.range;
        if (oneRange.length == 0) continue;
        oneRange.location -= cutLength;
        NSString *subStr = [text.string substringWithRange:NSMakeRange(oneRange.location+1, oneRange.length-2)];
        CGFloat fontSize = 12; // CoreText default value
        CTFontRef font = (__bridge CTFontRef)([text yy_attribute:NSFontAttributeName atIndex:oneRange.location]);
        if (font) fontSize = CTFontGetSize(font);
        NSMutableAttributedString *atr = [[NSMutableAttributedString alloc] initWithString:subStr];
        [text replaceCharactersInRange:oneRange withString:atr.string];
        [text yy_removeDiscontinuousAttributesInRange:NSMakeRange(oneRange.location, atr.length)];
        [text addAttributes:atr.yy_attributes range:NSMakeRange(oneRange.location, atr.length)];
        selectedRange = [self _replaceTextInRange:oneRange withLength:atr.length selectedRange:selectedRange];
        NSRange bindlingRange = NSMakeRange(oneRange.location, oneRange.length-2);
        YYTextBinding *binding = [YYTextBinding bindingWithDeleteConfirm:YES];
        [text yy_setTextBinding:binding range:bindlingRange]; /// Text binding
        [text yy_setColor:[UIColor colorWithRed:0.000 green:0.519 blue:1.000 alpha:1.000] range:bindlingRange];
        cutLength += 2;

    }
    NSArray *gapMatches = [_gapRegex matchesInString:text.string options:kNilOptions range:NSMakeRange(0, text.length)];
    if (gapMatches.count == 0) return NO;

//    NSRange lastOneRange = NSMakeRange(0, 0);
    NSMutableArray *gapRangeTempArr = [NSMutableArray array];
    for (NSUInteger i = 0, max = gapMatches.count; i < max; i++) {
        NSTextCheckingResult *one = gapMatches[i];
        NSRange oneRange = one.range;
        YYTextDecoration *decoration = [YYTextDecoration new];
        [text yy_setTextUnderline:decoration range:oneRange];
        [gapRangeTempArr addObject:NSStringFromRange(oneRange)];

    }
    self.gapRangeArr  = gapRangeTempArr;
    if (range) *range = selectedRange;
    
    return changed;
}

@end

在YYTextView.m的deleteBackward方法里加了一段代码：

if (binding && binding.deleteConfirm) {
            if ([self.delegate respondsToSelector:@selector(textViewShouldDeleteBinding:)]) {
                if (![self.delegate textViewShouldDeleteBinding:self]) {
                    return;
                }
            }
            _state.deleteConfirm = YES;
            [_inputDelegate selectionWillChange:self];
            _selectedTextRange = [YYTextRange rangeWithRange:effectiveRange];
            _selectedTextRange = [self _correctedTextRange:_selectedTextRange];
            [_inputDelegate selectionDidChange:self];
            
            [self _updateOuterProperties];
            [self _updateSelectionView];
            return;
        }

就是在删除的时候，如果是binding的字符串，就return；

好啦，就这样吧！第一次发文章😄