Adding a Property Page (ATL Tutorial, Part 6)

Artículo
04/24/2015

Property pages are implemented as separate COM objects, which allow them to be shared if required. In this step, you will do the following tasks to add a property page to the control:

Creating the Property Page Resource
Adding Code to Create and Manage the Property Page
Adding the Property Page to the Control

Creating the Property Page Resource

To add a property page to your control, use the ATL Add Class Wizard.

To add a Property Page

In Solution Explorer, right-click Polygon.
On the shortcut menu, click Add, and then click Add Class.
From the list of templates, select ATL Property Page and click Add.
When the ATL Property Page Wizard appears, enter PolyProp as the Short name.
Click Strings to open the Strings page and enter &Polygon as the Title.

The Title of the property page is the string that appears in the tab for that page. The Doc string is a description that a property frame uses to put in a status line or tool tip. Note that the standard property frame currently does not use this string, so you can leave it with the default contents. You will not generate a Help file at the moment, so delete the entry in that text box.
Click Finish, and the property page object will be created.

The following three files are created:

File	Description
PolyProp.h	Contains the C++ class CPolyProp, which implements the property page.
PolyProp.cpp	Includes the PolyProp.h file.
PolyProp.rgs	The registry script that registers the property page object.

The following code changes are also made:

The new property page is added to the object entry map in Polygon.cpp.
The PolyProp class is added to the Polygon.idl file.
The new registry script file PolyProp.rgs is added to the project resource.
A dialog box template is added to the project resource for the property page.
The property strings that you specified are added to the resource string table.

Now add the fields that you want to appear on the property page.

To add fields to the Property Page

In Solution Explorer, double-click the Polygon.rc resource file. This will open Resource View.
In Resource View, expand the Dialog node and double-click IDD_POLYPROP. Note that the dialog box that appears is empty except for a label that tells you to insert your controls here.
Select that label and change it to read Sides: by altering the Caption text in the Properties window.
Resize the label box so that it fits the size of the text.
Drag an Edit control from the Toolbox to the right of the label.
Finally, change the ID of the Edit control to IDC_SIDES using the Properties window.

This completes the process of creating the property page resource.

Adding Code to Create and Manage the Property Page

Now that you have created the property page resource, you need to write the implementation code.

First, enable the CPolyProp class to set the number of sides in your object when the Apply button is pressed.

To modify the Apply function to set the number of sides

Replace the Apply function in PolyProp.h with the following code:

STDMETHOD(Apply)(void)
{
   USES_CONVERSION;
   ATLTRACE(_T("CPolyProp::Apply\n"));
   for (UINT i = 0; i < m_nObjects; i++)
   {
      CComQIPtr<IPolyCtl, &IID_IPolyCtl> pPoly(m_ppUnk[i]);
      short nSides = (short)GetDlgItemInt(IDC_SIDES);
      if FAILED(pPoly->put_Sides(nSides))
      {
         CComPtr<IErrorInfo> pError;
         CComBSTR strError;
         GetErrorInfo(0, &pError);
         pError->GetDescription(&strError);
         MessageBox(OLE2T(strError), _T("Error"), MB_ICONEXCLAMATION);
         return E_FAIL;
      }
   }
   m_bDirty = FALSE;
   return S_OK;
}

A property page can have more than one client attached to it at a time, so the Apply function loops around and calls put_Sides on each client with the value retrieved from the edit box. You are using the CComQIPtr class, which performs the QueryInterface on each object to obtain the IPolyCtl interface from the IUnknown interface (stored in the m_ppUnk array).

The code now checks that setting the Sides property actually worked. If it fails, the code displays a message box displaying error details from the IErrorInfo interface. Typically, a container asks an object for the ISupportErrorInfo interface and calls InterfaceSupportsErrorInfo first, to determine whether the object supports setting error information. You can skip this task.

CComPtr helps you by automatically handling the reference counting, so you do not need to call Release on the interface. CComBSTR helps you with BSTR processing, so you do not have to perform the final SysFreeString call. You also use one of the various string conversion classes, so you can convert the BSTR if necessary (this is why the USES_CONVERSION macro is at the start of the function).

You also need to set the property page's dirty flag to indicate that the Apply button should be enabled. This occurs when the user changes the value in the Sides edit box.

To handle the Apply button

In Class View, right-click CPolyProp and click Properties on the shortcut menu.
In the Properties window, click the Events icon.
Expand the IDC_SIDES node in the event list.
Select EN_CHANGE, and from the drop-down menu to the right, click <Add> OnEnChangeSides. The OnEnChangeSides handler declaration will be added to Polyprop.h, and the handler implementation to Polyprop.cpp.

Next, you will modify the handler.

To modify the OnEnChangeSides method

Add the following code in Polyprop.cpp to the OnEnChangeSides method (deleting any code that the wizard put there):

LRESULT CPolyProp::OnEnChangeSides(WORD /*wNotifyCode*/, WORD /*wID*/, 
   HWND /*hWndCtl*/, BOOL& /*bHandled*/)
{
   SetDirty(TRUE);

   return 0;
}

OnEnChangeSides will be called when a WM_COMMAND message is sent with the EN_CHANGE notification for the IDC_SIDES control. OnEnChangeSides then calls SetDirty and passes TRUE to indicate the property page is now dirty and the Apply button should be enabled.

Adding the Property Page to the Control

The ATL Add Class Wizard and the ATL Property Page Wizard do not add the property page to your control for you automatically, because there could be multiple controls in your project. You will need to add an entry to the control's property map.

To add the property page

Open PolyCtl.h and add this line to the property map:

PROP_ENTRY_TYPE("Sides", 1, CLSID_PolyProp, VT_INT)

The control's property map now looks like this:

BEGIN_PROP_MAP(CPolyCtl)
   PROP_DATA_ENTRY("_cx", m_sizeExtent.cx, VT_UI4)
   PROP_DATA_ENTRY("_cy", m_sizeExtent.cy, VT_UI4)
#ifndef _WIN32_WCE
   PROP_ENTRY_TYPE("FillColor", DISPID_FILLCOLOR, CLSID_StockColorPage, VT_UI4)
#endif
   PROP_ENTRY_TYPE("Sides", 1, CLSID_PolyProp, VT_INT)
   // Example entries
   // PROP_ENTRY("Property Description", dispid, clsid)
   // PROP_PAGE(CLSID_StockColorPage)
END_PROP_MAP()

You could have added a PROP_PAGE macro with the CLSID of your property page, but if you use the PROP_ENTRY macro as shown, the Sides property value is also saved when the control is saved.

The three parameters to the macro are the property description, the DISPID of the property, and the CLSID of the property page that has the property on it. This is useful if, for example, you load the control into Visual Basic and set the number of Sides at design time. Because the number of Sides is saved, when you reload your Visual Basic project, the number of Sides will be restored.

Building and Testing the Control

Now build that control and insert it into ActiveX Control Test Container. In Test Container, on the Edit menu, click PolyCtl Class Object. The property page appears; click the Polygon tab.

The Apply button is initially disabled. Start typing a value in the Sides box and the Apply button will become enabled. After you have finished entering the value, click the Apply button. The control display changes, and the Apply button is again disabled. Try entering an invalid value. You will see a message box containing the error description that you set from the put_Sides function.

Next, you will put your control on a Web page.

Back to Step 5 | On to Step 7

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