How can i create a ComboBox like the System Tools->Attributes->Active Level Combobox?

I used mdlLevelList_getLevelNamesWithAttributes to get the level listmodel,and passed it to my Combobox.

The problem is when i use mdlDialog_comboBoxSetPopupState to make my ComboBox dropdown listbox stay opening,I found it'll cause a fault.

I chick the second col to display my level like the system do. .

Here I use mdlDialog_comboBoxSetPopupState to make the dorpdown stay opening in hook with the message DITEM_MESSAGE_STATECHANGED.

Then I chick the system level combobox.

It actually shows my ComboBox dropdown.

I tracked the hook message,and found that there is no focusout in Toolbox.This maybe why the fault caused.

Here is my  Rscs:

DialogBoxRsc DIALOGID_Operate = 
{
	DIALOGATTR_DEFAULT | DIALOGATTR_GROWABLE | DIALOGATTR_DOCKABLE,
	0,0,
	NOHELP,MHELP,
	NOHOOK,
	NOPARENTID,
	"",
	{
		{{0,0,0,0},ToolBox,TOOLBOXID_PC,ON,0,"",""},
	}
};

DItem_ToolBoxRsc TOOLBOXID_PC =
{
    NOHELP, MHELPTOPIC, NOHOOK, NOARG, 0, "",
	{
		{{10,0.5*YC,12*XC,1.5*YC}, ComboBox, COMBOBOXID_DataLevel, ON, 0, "", ""},
	}
};

//
DItem_ComboBoxRsc COMBOBOXID_DataLevel = 
{
    NOCMD, LCMD, NOSYNONYM, NOHELP, MHELP,
    HOOKITEMID_DataLevel_ComboBox, NOARG,
    128, "", "", "", "", NOMASK,
    0, 12, 0, 28*XC, 0,
    COMBOATTR_DRAWPREFIXICON | COMBOATTR_READONLY,
    "",
    "",
	{
    {12*XC, 128, ALIGN_LEFT, ""},
	{4*XC, 128, ALIGN_LEFT, ""},
	{4*XC, 128, ALIGN_LEFT, ""},
	{4*XC, 128, ALIGN_LEFT, ""},
	}
};

If someone have done something like this befor?