WinCE平台下C＃引用API（GDI）一个值得警惕的内存泄漏

由于C＃精简框架集绘图函数不支持圆角矩形，所以引用了相关的API。

[DllImport("//windows//coredll.dll", EntryPoint = "RoundRect")]
private static extern int CeRoundRect(IntPtr hdc, int X1, int Y1, int X2, int Y2, int X3, int Y3);

这是有内存泄漏的源码：

public static int RoundRect(Graphics e, Pen pen, SolidBrush brush, int X1, int Y1, int X2, int Y2, int X3, int Y3)
{
IntPtr hpen;
IntPtr hbrush;

if(pen!=null)
{
hpen = CreatePen((DashStyle.Solid == pen.DashStyle) ? 0 : 1,
(int)pen.Width, SetRGB(pen.Color.R, pen.Color.G, pen.Color.B)); //创建GDI画笔
}
else
{
hpen = GetStockObject(8); //空画笔
}

if (brush!= null)
{
hbrush = CreateSolidBrush(SetRGB(brush.Color.R, brush.Color.G, brush.Color.B)); //brush.Color.ToArgb());
}
else
{
hbrush = GetStockObject(5);
}

//pen.Dispose();
//brush.Dispose();

IntPtr hdc = e.GetHdc();
//---------------------
SelectObject(hdc, hbrush);
SelectObject(hdc, hpen);

int intRet=RoundRect(hdc, X1, Y1, X2,Y2, X3, Y3);

DeleteObject(hbrush);
DeleteObject(hpen);
//---------------------
e.ReleaseHdc(hdc);
return intRet;
}

这是没有问题的源码：

public static int RoundRect(Graphics e, Pen pen, SolidBrush brush, int X1, int Y1, int X2, int Y2, int X3, int Y3)
{
IntPtr hpen,old_pen;
IntPtr hbrush, old_brush;

if(pen!=null)
{
hpen = CreatePen((DashStyle.Solid == pen.DashStyle) ? 0 : 1,
(int)pen.Width, SetRGB(pen.Color.R, pen.Color.G, pen.Color.B)); //创建GDI画笔
}
else
{
hpen = GetStockObject(8); //空画笔
}

if (brush!= null)
{
hbrush = CreateSolidBrush(SetRGB(brush.Color.R, brush.Color.G, brush.Color.B)); //brush.Color.ToArgb());
}
else
{
hbrush = GetStockObject(5);
}

//pen.Dispose();
//brush.Dispose();

IntPtr hdc = e.GetHdc();
//---------------------
old_brush=SelectObject(hdc, hbrush);
old_pen=SelectObject(hdc, hpen);

int intRet=RoundRect(hdc, X1, Y1, X2,Y2, X3, Y3);

SelectObject(hdc, old_brush);
SelectObject(hdc, old_pen);
DeleteObject(hbrush);
DeleteObject(hpen);
//---------------------
e.ReleaseHdc(hdc);
return intRet;
}

看出代码的区别来了没有？泄漏的原因其实很简单，就是没有重新选入旧的画笔画刷。同样的程序（当然PC端的API库是GDI32）在上位机Window XP平台上没有什么问题（测试大约3天以上），而在WinCE平台确非常明显，大约1～3个小时（视圆角矩形绘图的多寡而定），该程序就会内存耗尽而死。