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Annotation of Examples/AppKit/Draw/graphicsUndo.subproj/SimpleGraphicsChange.m, revision 1.1.1.1

1.1       root        1: #import "drawundo.h"
                      2: 
                      3: /*
                      4:  * Please refer to external documentation about Draw
                      5:  * with Undo for information about what SimpleGraphicsChange 
                      6:  * is and where it fits in.
                      7:  */
                      8: 
                      9: @interface SimpleGraphicsChange(PrivateMethods)
                     10: 
                     11: - undoDetails;
                     12: - redoDetails;
                     13: - (BOOL)subsumeIdenticalChange:change;
                     14: 
                     15: @end
                     16: 
                     17: @implementation SimpleGraphicsChange
                     18: 
                     19: - saveBeforeChange
                     20: {
                     21:     [super saveBeforeChange];
                     22:     [changeDetails makeObjectsPerform:@selector(recordDetail)];
                     23: 
                     24:     return self;
                     25: }
                     26: 
                     27: - (BOOL)subsumeChange:change
                     28: /*
                     29:  * ChangeManager will call subsumeChange: when we are the last 
                     30:  * completed change and a new change has just begun. We override
                     31:  * the subsumeChange: to offer our subclasses a chance to
                     32:  * consolidate multiple changes into a single change.
                     33:  * First we check to make sure that the new change is of the
                     34:  * same class as the last. If it is then we check to make sure
                     35:  * that it's operating on the same selection. If not we simply
                     36:  * return NO, declining to subsume it. If it does operate on
                     37:  * the same change then we offer our subclass a change to 
                     38:  * subsume it by sending [self subsumeIdenticalChange:change].
                     39:  *
                     40:  * For example, if the user presses the up arrow key to move
                     41:  * a graphic up one pixel, that immediately becomes a complete,
                     42:  * undoable change, as it should. If she continues to press
                     43:  * use the arrow keys we don't want to end up making hundreds
                     44:  * of independent move changes that would each have to be
                     45:  * undone seperately. So instead we have the first move
                     46:  * subsume all subsequent MoveGraphicsChanges that operate
                     47:  * on the same selection.
                     48:  */
                     49: {
                     50:     BOOL               identicalChanges = NO;
                     51:     List               *selectedGraphics;
                     52:     int                        count, i;
                     53: 
                     54:     if ([change isKindOf:[self class]]) {
                     55:        if (!graphicsToChange) {
                     56:            identicalChanges = YES;
                     57:            selectedGraphics = [graphicView selectedGraphics];
                     58:            count = [selectedGraphics count];
                     59:            for (i = 0; (i < count) && (identicalChanges); i++) {
                     60:                if ([graphics objectAt:i] != [selectedGraphics objectAt:i])
                     61:                    identicalChanges = NO;
                     62:            }
                     63:        }
                     64:     } 
                     65:     if (identicalChanges)
                     66:         return [self subsumeIdenticalChange:change];
                     67:     else
                     68:         return NO;
                     69: }
                     70: 
                     71: - undoDetails
                     72: {
                     73:     [changeDetails makeObjectsPerform:@selector(undoDetail)];
                     74:     return self;
                     75: }
                     76: 
                     77: - redoDetails
                     78: {
                     79:     [changeDetails makeObjectsPerform:@selector(redoDetail)];
                     80:     return self;
                     81: }
                     82: 
                     83: - (BOOL)subsumeIdenticalChange:change
                     84: {
                     85:     return NO;
                     86: }
                     87: 
                     88: @end

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