CEdit numeric validation event C++ MFC

Question

I have a CEdit text box which is a part of a property pane and only allows numeric values (positive integers). The box works fine when people enter non-numeric values, but when they delete the value in the box a dialog pops up saying: "Please enter a positive integer."

Here is the situation:
1. I have a number (say 20) in the box.
2. I delete the number.
3. I get the error dialog.
Could anybody tell me how I can intercept this event and put a default value in there?

Here is what my property pane looks like:

const int DEFAULT_VALUE = 20;

class MyPropertyPane:public CPropertyPane
{
    //....
private:
    CEdit m_NumericBox;
    int   m_value;

    //....
public:
    afx_msg void OnEnChangeNumericBox();

    //....
}
void MyPropertyPane::MyPropertyPane()
{
   // Set a default value
   m_value = DEFAULT_VALUE;
}

//....
void MyPropertyPane::DoDataExchange(CDataExchange* pDX)
{
    DDX_Control(pDX, IDC_NUMERIC_BOX, m_NumericBox);

    // this sets the displayed value to 20
    DDX_Text(pDX, IDC_NUMERIC_BOX, m_value);
}

//....
void MyPropertyPane::OnEnChangeNumericBox()
{
    // Somebody deleted the value in the box and I got an event
    // saying that the value is changed.

    // I try to get the value from the box by updating my data
    UpdateData(TRUE);

    // m_value is still 20 although the value is 
    // deleted inside the text box.
}

Solution

The message you are receiving is coming from the data validation routines, not the data exchange routines. There is probably a call like this in DoDataExchange():

void MyPropertyPane::DoDataExchange(CDataExchange* pDX)
{
    DDX_Control(pDX, IDC_NUMERIC_BOX, m_NumericBox);
    DDX_Text(pDX, IDC_NUMERIC_BOX, m_value);
    DDV_MinMaxInt(pDX, m_value, 1, 20); // if the value in m_value is outside the range 1-20, MFC will pop up an error dialog
}

You can fix this problem by removing the built-in MFC data validation and adding your own:

void MyPropertyPane::DoDataExchange(CDataExchange* pDX)
{
    DDX_Control(pDX, IDC_NUMERIC_BOX, m_NumericBox);
    DDX_Text(pDX, IDC_NUMERIC_BOX, m_value);

    if( m_value < 1 || m_value > 20 )
    {
        m_value = DefaultValue;
    }
}

Comments

[Kiril]

But the m_value is still 20 even after it has been deleted... so checking if m_value < 1 will return false and the m_value will not be set to the DEFAULT_VALUE. The pop-up error "Please enter a positive integer" occurs before the OnChange event.

[Kiril]

Actually correction.. in DoDataExchange it doesn't even get past the DDX_Text(pDX, IDC_NUMERIC_BOX, m_value) so it wouldn't even hit the validation code.

[John Dibling]

This works in many cases, but it is often best to do all the data exchange & validation within the DoDataExchange() function because OnEnChangeNumericBox() may not be the only place where m_value is changed. For example if you have a radio button that changes m_value to preset values.

[Kiril]

Good point, in general the DoDataExchange() function is probably the best place to do validations... my example is a bit of an exception.

[sergiol]

How can the user enter a 0?