MxDrawUiPrEntity getEntity = new MxDrawUiPrEntity();

        getEntity.message = "选择实体";      

        // 设置选择过滤条件.

        MxDrawResbuf selFilter = new MxDrawResbuf();        

        // 5020是实体类型的DXF组码. DIM是类型。        

        selFilter.AddStringEx("ALIGNEDDIMENSION",5020);

        getEntity.setFilter(selFilter);        

        // 开始选择实体。

        if(getEntity.go() != MCAD_McUiPrStatus.mcOk)            

        return;        

        // 得到选择的实体.

        MxDrawEntity ent = getEntity.Entity();        

        if (ent == null)            

        return;        

        if (!(ent is MxDrawDimAligned) )

        {            

        return;

        }        

        // 得到选择的标注.

        MxDrawDimAligned dimAligned = (MxDrawDimAligned)ent;        

        // 尺寸标注改成60

        double dNewDist = 60.0;        

        // 当前标注的两个点坐标。        

        MxDrawPoint pt1 = dimAligned.XLine1Point;

        MxDrawPoint pt2 = dimAligned.XLine2Point;        

        // 计算pt1到pt2的向量.

        MxDrawVector3d vec = pt2.SumVector(pt1);        

        // 把向量单位化

        vec.Normalize();        

        //把向长度变成新距离.

        vec.Mult(dNewDist);        

        // 算出在新距离下的新的坐标点。

        MxDrawPoint newPt = new MxDrawPoint();

        newPt.x = pt1.x;

        newPt.y = pt1.y;

        newPt.Add(vec);    

        // 修改尺寸标注.

        dimAligned.XLine2Point = newPt;

        dimAligned.RecomputeDimBlock(true);        

        // 查找尺寸标的直线段。并修改它。

        MxDrawResbuf filter = new MxDrawResbuf();

        filter.AddStringEx("LINE",5020);

        MxDrawSelectionSet ss = new MxDrawSelectionSet();        

        // 得到标注的开始点上的实体.

        // 搜索精度。

        double dTol = 10;//axMxDrawX1.ViewLongToDocCoord(3);

        MxDrawPoint selPt1 = new MxDrawPoint();

        MxDrawPoint selPt2 = new MxDrawPoint();

        selPt1.x = pt1.x - dTol;

        selPt1.y = pt1.y - dTol;

        selPt2.x = pt1.x + dTol;

        selPt2.y = pt1.y + dTol;

        ss.Select(MCAD_McSelect.mcSelectionSetCrossing, selPt1, selPt2, filter);    

        // 可能会得到多个实体，遍历所有实体，找到标注的直线对象。

        for(int i = 0;  i < ss.Count;i++)

        {

            MxDrawEntity findEnt = ss.Item(i);            

            if (!(findEnt is MxDrawLine))

            {                

            continue;

            }

            MxDrawLine line = (MxDrawLine)findEnt;            

            // 得到直线的两个点坐标。            

            MxDrawPoint sPt = line.StartPoint;

            MxDrawPoint ePt = line.EndPoint;            

            double dDis1 = sPt.DistanceTo(pt1);            

            double dDis2 = ePt.DistanceTo(pt1);            

            if(dDis1 > dDis2)

            {                

            if (dDis2 > dTol)                    

            continue;                

            if(sPt.DistanceTo(pt2) > dTol)                    

            continue;                

            // 直线的开始点，在pt2附近

                line.StartPoint = newPt;                

                break;

            }            

            else

            {                

            if(dDis1 > dTol)                    

            continue;               

             if(ePt.DistanceTo(pt2) > dTol)                    

             continue;                

             // 直线的结束点，在pt2附近

                line.EndPoint = newPt;                

                break;

            }

        }

        axMxDrawX1.ZoomAll();