iOS UITextView 首行缩进 撤销输入 反撤销输入的实现代码

#import "ViewController.h"
@interface ViewController ()<UITextViewDelegate>{
  UITextView *_textView;
  NSUndoManager *_undomanager;
  NSInteger _length;
  UIButton *undobutton;
  UIButton *redobutton;
}
@end
@implementation ViewController
- (void)viewDidLoad {
  [super viewDidLoad];
  UIBarButtonItem *undoItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemUndo target:self action:@selector(undoitem)];
  UIBarButtonItem *redoItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemRedo target:self action:@selector(redoitem)];
  self.navigationItem.leftBarButtonItem = undoItem;
  self.navigationItem.rightBarButtonItem = redoItem;
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyBoardShow:) name:UIKeyboardWillShowNotification object:nil];
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyBoardHidden:) name:UIKeyboardWillHideNotification object:nil];
  _length = 0;
//初始化NSUndoManager
  _undomanager = [[NSUndoManager alloc] init];
  _textView = [[UITextView alloc]initWithFrame:CGRectMake(0, 200, self.view.frame.size.width, 400)];
  _textView.backgroundColor = [UIColor yellowColor];
  _textView.delegate = self;
  _textView.font = [UIFont systemFontOfSize:15];
  _textView.layer.cornerRadius = 5;
  _textView.layer.masksToBounds = YES;
  _textView.textColor = [UIColor blackColor];
  _textView.text = @" ";//要设置初始文本,不然段落体现不出来。
  NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
  paragraphStyle.lineSpacing = 5;  //行间距
  paragraphStyle.firstLineHeadIndent = 30;  /**首行缩进宽度*/
  paragraphStyle.alignment = NSTextAlignmentLeft;
  NSDictionary *attributes = @{
                 NSFontAttributeName:[UIFont systemFontOfSize:13],
                 NSParagraphStyleAttributeName:paragraphStyle
                 };
  _textView.attributedText = [[NSAttributedString alloc] initWithString:_textView.text attributes:attributes];
//监听textview文本改动的通知
 [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(changeTextViewText) name:UITextViewTextDidChangeNotification object:nil];
  [self.view addSubview:_textView];
}
-(void)redoitem{
  //反撤销
  [_undomanager redo];
}
-(void)undoitem{
  //撤销
  [_undomanager undo];
}
-(void)keyBoardShow:(NSNotification *)noti{
  NSDictionary *dic = noti.userInfo;
  NSValue *aValue = [dic objectForKey:UIKeyboardFrameEndUserInfoKey];
  CGRect keyboardRect = [aValue CGRectValue];
  int height = keyboardRect.size.height;
  [_textView setContentInset:UIEdgeInsetsMake(0, 0, height, 0)];
}
-(void)keyBoardHidden:(NSNotification *)noti{
  [_textView setContentInset:UIEdgeInsetsMake(0, 0, 0, 0)];
}
- (void)setMyObjectTitle:(NSString *)newTitle{
  //判断当前NSUndoManager的状态，是处于撤销或者反撤销的状态
-(void)textViewDidChange:(UITextView *)textView
  if (_undomanager.isUndoing) {
    NSInteger length = newTitle.length;
    if (_textView.text.length>0) {
      //获取 
      _textView.text = [_textView.text substringWithRange:NSMakeRange(0, _textView.text.length - length)];
      [_undomanager registerUndoWithTarget:self
                    selector:@selector(setMyObjectTitle:)
                     object:newTitle];
    }
  }else if (_undomanager.isRedoing){
    _textView.text = [_textView.text stringByAppendingString:newTitle];
    [_undomanager registerUndoWithTarget:self
                  selector:@selector(setMyObjectTitle:)
                   object:newTitle];
  }else{
    NSString *currentText = _textView.text;
    if (newTitle != currentText) {
      _textView.text = currentText;
      [_undomanager registerUndoWithTarget:self
                    selector:@selector(setMyObjectTitle:)
                     object:newTitle];
    }else{
      _textView.text = newTitle;
    }
  }
}
-(void)changeTextViewText{
  if (_textView.text.length>0) {
    undobutton.enabled = YES;
  }else{
    undobutton.enabled = NO;
    redobutton.enabled = NO;
  }
  NSString *text ;
  if (_length != 0) {
    NSInteger textLength = _textView.text.length;
    if (textLength > _length) {
      NSInteger newLength = textLength - _length;
      text = [NSString stringWithFormat:@"%@",[_textView.text substringWithRange:NSMakeRange(_length, newLength)]];
    }else{
      text = _textView.text;
    }
  }else{
    text = _textView.text;
  }
  _length = _textView.text.length;
  [self setMyObjectTitle:text];
}