activeView addDelegate: addExtension:: addShapesForTest boundingBox canRedo canUndo changeCount clearCachedData clearShapes clearShapes: cmdView cmdViewHandle combineRegen: command content createDummyView: createGraphView:: createGraphView:inView:flags: createMagnifierView:refView:parentView: currentModelPoint currentPoint displayExtent displayRectToModel: displayToModel: drawCount endArrowHead eraseView exportExtentAsPNG:space: exportLayers exportLayersForShape: exportLayerTree: exportPathsForShape: exportPNG: exportSVG: exportSVGPath: extentSnapshot: fillAlpha fillColor findShapeByImageID: findShapeByTag: getHandlePoint:index: getImageFromSVGFile:maxSize: getImagePath getImageShapes getImageSize:shape: getModelBox: getRecordTicks getShapeBox: hasImageShape importSVGPath:d: initWithView: insertImageFromFile: insertImageFromFile:center:tag: insertPNGFromResource: insertPNGFromResource:center: insertSVGFromResource: insertSVGFromResource:center: isCommand: isPaused isPlaying isRecording lineAlpha lineColor lineStyle lineWidth loadFromFile: loadFromFile:readOnly: localizedString: modelBox options redo removeDelegate: removeSubviews: saveToFile: selectedCount selectedHandle selectedIds selectedShapeID selectedType setCommand:withParam: setContextEditing: setExtraContextImages: setImagePath: setOption:forKey: shapeCount shapeFactory sharedInstance sharedInstance: showMessage: snapshot snapshotWithShapes:size: startArrowHead startRecord: startUndoRecord: stopRecord stopUndoRecord strokeWidth switchCommand undo unlockedShapeCount version view viewBox viewCenter viewScale visibleShapeCount zoomEnabled zoomPan: zoomToExtent zoomToExtent: zoomToModel:

canUndo() - (BOOL) canUndo 能否撤销