对象引用没有设置到对象实例的原因很多：
待续。。。
1、如下：
public int Revise( ref int numline, ref int numcircle, ref int numtext,System.IO. StreamWriter str_w, List < string > record, EXT extend, Line [] lines, Circle [] circles, Text [] texts)
{
string [] record1 =record.ToArray();
for ( int i = 0; i < record1.Length;i++ )
{
string temp = string .Empty;
temp = record1[i];
if (temp == "$EXTMIN" )
{
record1[i + 2] = Convert .ToString(extend.Min_x) ;
record1[i + 4] = Convert .ToString(extend.Min_y);
record1[i + 6] = Convert .ToString(extend.min_z);
record1[i + 10] = Convert .ToString(extend.Max_x);
record1[i + 12] = Convert .ToString(extend.Max_y);
record1[i + 14] = Convert .ToString(extend.Max_z);
i += 14;
continue ;
}
if (temp == "AcDbLine" )
{
record1[i + 2]= Convert .ToString(lines[numline].x1);//此处开始报错
record1[i + 4] = Convert .ToString(lines[numline].y1);
record1[i + 6] = Convert .ToString(lines[numline].z1);
record1[i + 8] = Convert .ToString(lines[numline].x2);
record1[i + 10] = Convert .ToString(lines[numline].y2) ;
record1[i + 12] = Convert .ToString(lines[numline].z2);
numline--;
i += 12;
continue ;
}
}
for ( int i = 0; i < record1.Length;i++ )
{
str_w.WriteLine(record1[i]);
}
return 1;
}
其中numline,numcircle,numtext，代表的line，circle，text对象的个数
原因就在于，数组的下标总是比个数小1，假如有5个元素，我们尝试给lines[5]赋值，而lines[5]已经越界，更不可能初始化。
2、对于数组，不光要实例化数组，还要实例化数组的对象
public int Read_Entities( ref int numpolyline, Polyline [] plines, System.IO. StreamReader str_r)
{
string buff = string .Empty;
buff = str_r.ReadLine();
//int numline = 0;
//int numcircle = 0;
//int numtext=0;
while (buff != "OBJECTS" )
{
if (buff == "LWPOLYLINE" )
{
while (buff != "AcDbPolyline" )
{
buff = str_r.ReadLine();
}
plines[numpolyline] = new Polyline ();//(1)
str_r.ReadLine();
plines[numpolyline].pointnum = Convert .ToInt32(str_r.ReadLine());
str_r.ReadLine();
str_r.ReadLine();
str_r.ReadLine();
str_r.ReadLine();
plines[numpolyline].points = new point [plines[numpolyline].pointnum];//(2)
for ( int i=0;i<plines[numpolyline].pointnum;i++)
{
plines[numpolyline].points[i] = new point ();//(3)
str_r.ReadLine();
plines[numpolyline].points[i].x = Convert .ToDouble(str_r.ReadLine());
str_r.ReadLine();
plines[numpolyline].points[i].y = Convert .ToDouble(str_r.ReadLine());
}
}
buff = str_r.ReadLine();
}
return 1;
}
其中，多线由多个点组成
注释（1）处：初始化polyline对象
注释（2）处：初试化point数组
注释（3）处：初始化点对象实例
一直忘记了第二个，导致一直提示错误