UndoSupportForNSTextStorage
The AppKit comes with undo support in the text system, but unfortunatly this support is provided by the NSTextView class, not the NSTextStorage class. Adding undo support to NSTextStorage would make it easier to support text undo in a number of cases... problem is the implementation.
Here is what I have so far. Seems to work for me on paper, but I'm doing something wrong and corupting the undo stack. The basic idea here is to commit partial edits (ones that might be merged with later edits) to a separate HBTextStorageEdit object. This is done so that I have a "handle" on these edits and can remove them from the undo stack when they need to be merged with later edits. When a situation arrises where the edits cannot be merged they are commited to the undo stack. By this "commit" I mean that the edits are placed on the undo stack with the NSTextStorage as the target, they won't be removed or merged with other edits after this commit.
So what do I need to do to get this thing working?
@interface HBTextStorage : NSTextStorage {
NSMutableAttributedString _textContents; HBTextStorageEdit _editInProgress;
}
@end
@implementation HBTextStorage
- (NSString )string {
return [_textContents string];
}
- (void)addAttribute:(NSString )name value:(id)value range:(NSRange)aRange {
[_textContents addAttribute:name value:value range:aRange]; // cover bug listed on cocoadev
}
- (NSDictionary )attributesAtIndex:(unsigned)index effectiveRange:(NSRangePointer)aRange {
return [_textContents attributesAtIndex:index effectiveRange:aRange];
}
- (void)setAttributes:(NSDictionary )attributes range:(NSRange)aRange {
[[self textContents] setAttributes:attributes range:aRange]; [self edited:NSTextStorageEditedAttributes range:aRange changeInLength:0];
}
- (void)replaceCharactersInRange:(NSRange)aRange withString:(NSString )aString {
NSUndoManager undoManager = [self undoManager]; NSRange insertedRange = NSMakeRange(aRange.location, [aString length]); int origLen = [self length]; BOOL commitThisChangeToUndoStack = NO;
if ([undoManager isUndoing] || [undoManager isRedoing]) {
[_editInProgress release];
_editInProgress = nil;
commitThisChangeToUndoStack = YES;
} else {
[undoManager removeAllActionsWithTarget:_editInProgress];
// 1. try to merge changes with edit in progress
if (![_editInProgress merge:aString range:aRange]) {
// 2. commit current edit if can't merge
[_editInProgress commitEditToUndoStack];
[_editInProgress release];
_editInProgress = nil;
BOOL singleInsert = [[[HBTextStorageEdit]] isSingleCharInsert:aString range:aRange];
BOOL singleDelete = [[[HBTextStorageEdit]] isSingleCharDelete:aString range:aRange];
// 3. start new edit in progress
if (singleInsert || singleDelete) {
_editInProgress = [[HBTextStorageEdit alloc]
initWithString:aString range:aRange target:self];
[[undoManager prepareWithInvocationTarget:_editInProgress] undoEdit];
// 4. commit edit
} else {
commitThisChangeToUndoStack = YES;
}
}
if (_editInProgress) {
[[undoManager prepareWithInvocationTarget:_editInProgress] undoEdit];
[undoManager setActionName:NSLocalizedString(@"Typing", @"")];
}
}
if (commitThisChangeToUndoStack) {
NSString replacedString = [[self string] substringWithRange:aRange];
[[undoManager prepareWithInvocationTarget:self]
replaceCharactersInRange:insertedRange withString:replacedString];
[undoManager setActionName:NSLocalizedString(@"Typing", @"")];
}
[[self textContents] replaceCharactersInRange:aRange withString:aString];
[self edited:NSTextStorageEditedCharacters range:aRange
changeInLength:[self length] - origLen];
}
@end
@interface HBTextStorageEdit : NSObject {
HBTextStorage _target; NSRange _editRange; NSString _replacedString;
}
+ (BOOL)isSingleCharInsert:(NSString )edit range:(NSRange)range; + (BOOL)isSingleCharDelete:(NSString )edit range:(NSRange)range;
- (id)initWithString:(NSString )string range:(NSRange)range target:(HBTextStorage )target; - (void)undoEdit; - (void)commitEditToUndoStack; - (BOOL)merge:(NSString )edit range:(NSRange)range;
@end
@implementation HBTextStorageEdit
+ (BOOL)isSingleCharInsert:(NSString )edit range:(NSRange)range {
return range.length == 0 && [edit length] == 1;
}
+ (BOOL)isSingleCharDelete:(NSString )edit range:(NSRange)range {
return range.length == 1 && [edit length] == 0;
}
- (id)initWithString:(NSString )string range:(NSRange)range target:(HBTextStorage )target {
if (self = [super init]) {
_target = target;
_editRange.location = range.location;
if (range.length == 0) {
_editRange.length = 1;
_replacedString = @"";
} else {
_editRange.length = 0;
_replacedString = [[[target string] substringWithRange:range] retain];
}
}
return self;
}
- (void)dealloc {
[_replacedString release]; [super dealloc];
}
- (void)undoEdit {
[[_target undoManager] removeAllActionsWithTarget:self]; [_target replaceCharactersInRange:_editRange withString:_replacedString];
}
- (void)commitEditToUndoStack {
NSUndoManager undoManager = [_target undoManager]; [[_target undoManager] removeAllActionsWithTarget:self]; [[undoManager prepareWithInvocationTarget:_target] replaceCharactersInRange:_editRange withString:_replacedString]; [undoManager setActionName:NSLocalizedString(@"Typing", @"")];
}
- (BOOL)merge:(NSString )edit range:(NSRange)range {
int currentCursor = _editRange.location + _editRange.length;
BOOL singleInsert = range.location == currentCursor
&& [[[HBTextStorageEdit]] isSingleCharInsert:edit range:range];
BOOL singleDelete = range.location == currentCursor - 1
&& [[[HBTextStorageEdit]] isSingleCharDelete:edit range:range];
if (singleInsert) {
_editRange.length++;
return YES;
} else if (singleDelete) {
if (_editRange.length > 0) {
_editRange.length--;
} else {
NSString temp = [[_target string] substringWithRange:range];
[_replacedString autorelease];
_replacedString = [[temp stringByAppendingString:_replacedString] retain];
_editRange.location--;
}
return YES;
}
return NO;
}
@end (wrapped the code so that it won't force hugely wide paragraphs on this page)
JesseGrosjean software(at)hogbay(dot)com
You want to be looking into http://developer.apple.com/techpubs/macosx/Cocoa/TasksAndConcepts/ProgrammingTopics/UndoArchitecture/index.html
There look for UndoGroups and be happy. :-)
I would (rather that looking at the previous event on the stack) determine which operations should start a new UndoGroup and then appropriately end the current UndoGroup.
Just a thought,
That's definitely the way to do it. -- KritTer
If using the UndoGroup approach would I need to turn of setGroupsByEvent:? I would be a little worried about this approach (if i understand it correctly) since every char insert/delete would need to be placed on the undo stack. I'd like to have infinite undo and if you type for a few hours this could get expensive??? Hit me over the head with the don't optimize it stupid until you know its slow if appropriate.
My current approach (I?ll post some code tonight, but it's not quite working) is to have a new object called TextEditInProgress. For edits to the NSTextStorage that can be merged (contiguous single char insert/delete in my implementation) the undo target is set to be this TextEditInProgress object. For each new replaceCharactersInRange I
1. Remove the current TextEditInProgress from the undo stack using removeTarget: 2. See if the new change can be merged with the current TextEditInProgress
- if yes
merge changes and place TextEditInProgress back on undo stack. This means that the NSTextStorage is not the target of the undo, the TextEditInProgress is.
- if no
commit changes in TextEditInProgress to undo stack. This means put those changes on stack with NSTextStorage as target... so TextEditInProgress is no longer on the undo stack.
3. if appropriate for the current change (if it is a single char insert/delete) then creat a new TextEditInProgress and put it on undo stack. Else commit the inverse change to the undo stack, NSTextStorage as target.
4. Apply change to the NSTextStorages backing NSMutableAttributedString.
Ok, that was probably very unclear, but maybe it gives you an idea of my current approach. The big point is it should avoid putting an invocation on the undo stack for each character typed, but it's not working yet, and who knows maybe it has some fundamental flaw that someone can point out to me.
Thanks for your comments, JesseGrosjean
Ignoring the undo issue for a moment, I would like to remind our readership that the custom text storage subclass listed above is an excellent starting point for more sophisticated auto-formatting / auto-completion projects that tend to come up at the same tim as syntax coloring. See also ImplementSyntaxHighlighting. -- MikeTrent
I've added my current code to the top of this page.
This may be orthogonal to your needs, but I think one reason that people want undo in NSTextStorage is because they need to programmatically insert or change text and have it be able to be undone. I was struggling with the same problem, but then I found that the easiest solution was to keep the modification in NSTextView and just notify it to record the changes. Here's my code -- I do everything with attributed strings, so I added "-insertAttributedText:" and "-insertText:withAttributes:". To change/insert text I simply set the selection and call one of these methods.
@implementation MyTextView
-(void)insertAttributedText:(NSAttributedString)astring {
NSRange range = [self selectedRange]; NSString insertingText = [astring string]; NSString selectedText = [[self string] substringWithRange:range]; NSString stringForDelegate = insertingText; // If only attributes are changing, pass nil. if ([insertingText isEqualToString:selectedText]) stringForDelegate = nil; // Call delegate methods to force undo recording if ([self shouldChangeTextInRange:range replacementString:stringForDelegate]) { [[self textStorage] replaceCharactersInRange:range withAttributedString:astring]; [self setSelectedRange: NSMakeRange(range.location+[astring length], 0)]; [self didChangeText]; }
}
-(void)insertText:(NSString)string withAttributes:(NSDictionary)attr {
NSAttributedString astring = [[NSAttributedString alloc] initWithString:string attributes:attr]; [self insertAttributedText:astring]; [astring release];
}
@end
The calls to -shouldChangeTextInRange:replacementString: and -didChangeText are sufficient to get the NSTextView to record the undo. Like I said, this may not be what you actually wanted :-) but it solved my problem. --DrewThaler
Though very rare, there are cases where there is no way around a custom implementation. One example is some structure in the text that covers deeper semantics and can not be represented by a plain attributed string without loosing that information at the same time. Thanks for the headstart, Jesse. --MaxSeelemann
