Thread: Visual C++ Problem, CComboBox

I am having a problem getting my combo box to drop down in Visual C++ here is the code.

Code:

void CBensVisTestDlg::OnDropdownCombo1() 
{
	CRect pos;

	pos.top = 0;
	pos.left = 0;
	pos.right = 100;
	pos.bottom = 250;

	CComboBox getFile;

	CComboBox();

	getFile.Create(CBS_DROPDOWNLIST | WS_VISIBLE | WS_CHILD, pos, this, IDC_COMBO1);

    getFile.Dir(DDL_DRIVES, "C:*.*");

	// TODO: Add your control notification handler code here
	
}

The program compiles with no errors or warnings and doesn't have any runtime errors once running, but when I click on the appropriate combo box basically nothing happens, could someone please tell me what I am doing wrong.

Thanks in advance.

Ben.

You are creating a new CComboBox object in the handler for the object the event is happening for. You need to then call this->Dir(DDL_DRIVES, "C:*.*") otherwise your calling that for a newly created CComboBox object.

You need to do this:

Code:

CComboBox* pCB = (CComboBox*)GetDlgItem(IDC_COMBO1);
pCB->Dir(DDL_DRIVES, "C:*.*");

// or

this->Dir(DDL_DRIVES, "C:*.*");

I am pretty sure I understand you, and I have revised my code to look like this:

Code:

void CBensVisTestDlg::OnDropdownCombo1() 
{
	CRect pos;

	pos.top = 0;
	pos.left = 0;
	pos.right = 100;
	pos.bottom = 250;

	CComboBox* getFile = new CComboBox;

    getFile->Dir(DDL_DRIVES, "C:\\*.*");

	CComboBox();

	getFile->Create(CBS_DROPDOWNLIST | WS_VISIBLE | WS_CHILD, pos, this, IDC_COMBO1);
	
}

I get an assertion error while trying to drop doen the combo box, I realise I haven't copied your code directly but when I did copy your code directly I again got an assertion error, can anyone explain how this combo box is supposed to work? This is doing my head in.

Thanks in advance.

Ben.

You're creating a new CComboBox object. You don't want to do that. You need to use the already in use one. Remember the event is triggered because you already have a CComboBox in existence. Just use this:

Code:

CComboBox* pCB = (CComboBox*)GetDlgItem(IDC_COMBO1);
pCB->Dir(DDL_DRIVES, "C:\\*.*");

That code will do what you want to do, because you have a combo box named IDC_COMBO1. The GetDlgItem() will get a CWnd pointer to the child window with the id passed to it. Then you type cast it back to the object type you need. In this case CComboBox*.

Sorry man, I get you now, you must have been getting well frustrated, right I was writing the code inside the handler for a combo box that was already created and then i was calling a constructor and create function for another combo box, it was bound to get ........ed off, when you showed me those lines of code I dint realise you dint mean just edit them it was JUST those lines of code I needed, right, you have really got me back on track now, again thanks a lot.

No doubt I'll be back again, sorry about that.

Ben.

No problem. You know I'll help you again next time too.