Get the position of the control in the Windows openfile dialog

Question

I my application, I have added a dropdown box to the standard windows file open dialog. This works fine, but I would like to position this drop box exactly below the file name and file mask edit controls, and its label exactly below the labels for these controls. How can I get the positions of these controls and the corresponding labels (it depends on the Windows version and maybe even on theming, so using the constants that make the dialog look fine on my computer won't do)?

Answer 1

On Vista+, you should be using the IFileDialog, IFileOpenDialog and IFileDialogCustomize interfaces:

Common Item Dialog

Customizing the Dialog

You can use the IFileDialogCustomize::AddText() and IFileDialogCustomize::AddComboBox() methods to add a drop-down list and its label to the dialog, and if needed use the IFileDialogControlEvents::OnItemSelected event to react to the user selecting items in your drop-down list.

However, you cannot decide where custom controls are displayed when customizing this dialog. UI layout is controlled by the dialog itself:

The Common Item Dialog implementation found in Windows Vista provides several advantages over the implementation provided in earlier versions:
...
•Enables simple customization of the dialog, such as setting the label on the OK button, without requiring a hook procedure.
•Supports more extensive customization of the dialog by the addition of a set of data-driven controls that operate without a Win32 dialog template. This customization scheme frees the calling process from UI layout. Since any changes to the dialog design continue to use this data model, the dialog implementation is not tied to the specific current version of the dialog.
...

The only layout access it provides is the order in which you add your custom controls, and any visual grouping. So, you could use IFileDialogCustomize::StartVisualGroup() to create a new group, then call AddText() and AddComboBox() (in that order) to add those controls to the group, and then finally call IFileDialogCustomize::EndVisualGroup().

On the other hand, when using GetOpenFileName() instead, there are some different options for customizing that dialog, and they allow you much finer grain control over the dialog's layout:

Customizing Common Dialog Boxes

Open and Save As Dialog Box Customization

The preferred option is to create a custom dialog box template and specify it in the OPENFILENAME structure. Within the template, you can have whatever controls and layout you want, and then the template can be inserted as a child of a standard Explorer-style dialog, or as a replacement for a standard Old-style dialog. MSDN documents how to custom-position a template within an Explorer-style dialog:

Explorer-Style Custom Templates

To make room for the new controls, the system expands the default dialog box by the width and height of the custom dialog box. By default, all controls from the custom dialog box are positioned below the controls in the default dialog box. However, you can override this default positioning by including a static text control in your custom dialog box template and assigning it the control identifier value of stc32. (This value is defined in the Dlgs.h header file.) In this case, the system uses the control as the point of reference for determining where to position the new controls. All new controls above and to the left of the stc32 control are positioned the same amount above and to the left of the controls in the default dialog box. New controls below and to the right of the stc32 control are positioned below and to the right of the default controls. In general, each new control is positioned so that it has the same position relative to the default controls as it had to the stc32 control. To make room for these new controls, the system adds space to the left, right, bottom, and top of the default dialog box as needed.

The alternative, without using a custom template, is to obtain the dialog's own HWND directly (which can be gotten inside a hook function assigned to the OPENFILENAME::lpfnHook field) and then you have full access to do whatever you want with the dialog. Microsoft assigned fixed control IDs to the standard controls of an Explorer-style dialog (so you must specify the OFN_EXPLORER flag for this approach to work), and those IDs are consistent across Windows versions. Those IDs are meant to be used with the CDM_SETCONTROLTEXT and CDM_HIDECONTROL messages, but they can also be used with GetDlgItem() to get the HWND of certain dialog controls, in this case the cmb13, edt1 and stc3 controls:

cmb13
Drop-down combo box that displays the name of the current file, allows the user to type the name of a file to open, and select a file that has been opened or saved recently. This is for earlier Explorer-compatible applications without hook or dialog template. Compare with edt1.

edt1
Edit control that displays the name of the current file, or allows the user to type the name of the file to open. Compare with cmb13.

stc3
Label for the cmb13 combo box and the edt1 edit control

Once you have those HWNDs, you can manually query their current positions and sizes, add your custom drop-down list underneath them as needed, and resize the dialog's HWND to accommodate your drop-down list.

Whether you use a template or direct HWND manipulation, you would need to use a dialog hook function to process messages from your drop-down list as needed, such as the CBN_SELCHANGE notification.