ExtendFlags含义0
Default = 0========================================================
// By default, extension considers both ends of parts. The old ends remain and new
// points are added at the extended ends. The new points have attributes that are
// extrapolated from adjacent existing segments.
//默认情况下，扩展将考虑零件的两端。旧的结局仍然是新的
//在延伸端添加点。新点具有以下属性
//从相邻的现有段推断。
RelocateEnds = 1,====================================================
// If an extension is performed at an end, relocate the end point to the new position
// instead of leaving the old point and adding a new point at the new position.
//如果在端点执行延伸，请将端点重新定位到新位置
//而不是离开旧点，在新位置添加新点。
KeepEndAttributes = 2,=================================================
// If an extension is performed at an end, do not extrapolate the end-segment's
// attributes for the new point. Instead, make its attributes the same as the current
// end. Incompatible with esriNoAttributes.
//如果在末端执行延伸，则不要推断末端段的
//新点的属性。相反，使其属性与当前属性相同
//结束。与esriNoAttributes不兼容。
NoEndAttributes = 4,=============================
//如果在末端执行延伸，则不要推断末端段的
//新点的属性。相反，将其属性设置为空。不相容的
//具有esriKeepAttributes。
// If an extension is performed at an end, do not extrapolate the end-segment's
// attributes for the new point. Instead, make its attributes be empty. Incompatible
// with esriKeepAttributes.