请教out参数的用法

Question

GetCursorPos是静态方法　要带上类名．GetCursorPos（）来调用完整的出错信息？

Answer 1

internal struct POINTAPI
  {
   internal int x;
   internal int y;
  }
[System.Runtime.InteropServices.DllImport( "user32.dll" , EntryPoint="GetCursorPos" )]
  internal extern static int GetCursorPos( ref POINTAPI lpPoint );
调用时
POINTAPI _POINTAPI = new POINTAPI();
GetCursorPos(out lppoint);
label1.Text = lppoint.x.ToString();
label2.Text = lppoint.y.ToString();

Answer 2

上面的改一下：
internal struct POINTAPI
  {
   internal int x;
   internal int y;
  }
[System.Runtime.InteropServices.DllImport( "user32.dll" , EntryPoint="GetCursorPos" )]
  internal extern static int GetCursorPos( ref POINTAPI lpPoint );
调用时
POINTAPI _POINTAPI = new POINTAPI();
GetCursorPos(ref lppoint);
label1.Text = lppoint.x.ToString();
label2.Text = lppoint.y.ToString();这样可以,或者用:internal struct POINTAPI
  {
   internal int x;
   internal int y;
  }
[System.Runtime.InteropServices.DllImport( "user32.dll" , EntryPoint="GetCursorPos" )]
  internal extern static int GetCursorPos( out POINTAPI lpPoint );
调用时
POINTAPI _POINTAPI = new POINTAPI();
GetCursorPos(out lppoint);
label1.Text = lppoint.x.ToString();
label2.Text = lppoint.y.ToString();

Answer 3

类型要匹配,如果用 class POINT ,就要这样:[DllImport("user32.dll")]
static extern bool GetCursorPos(POINT lpPoint);
调用时直接:GetCursorPos(lppoint);struct 类型就要:
[System.Runtime.InteropServices.DllImport( "user32.dll" , EntryPoint="GetCursorPos" )]
internal extern static int GetCursorPos( out POINTAPI lpPoint );
调用时: GetCursorPos(out lppoint);
如果[System.Runtime.InteropServices.DllImport( "user32.dll" , EntryPoint="GetCursorPos" )]
internal extern static int GetCursorPos( ref POINTAPI lpPoint );
调用时: GetCursorPos(ref lppoint);

Answer 4

POINT lppoint;
GetCursorPos(out lppoint);
label1.Text = lppoint.x.ToString();
label2.Text = lppoint.y.ToString();