Add wxSpinCtrl::SetIncrement() and implement it for all ports

SetIncrement() was already available in wxSpinCtrlDouble and GTK version
of wxSpinCtrl, now implement support for it in wxMSW and wxOSX as well.

In fact, in wxMSW, implement it at wxSpinButton level, so that both this
class and wxSpinCtrl inheriting from it (in wxMSW only) support setting
custom increment now.

Also add support for it to XRC, show it in the sample and add a unit
test verifying that it works.

Closes #2597.

samples/widgets/spinbtn.cpp

@@ -55,11 +55,13 @@ enum
     SpinBtnPage_SetValue,
     SpinBtnPage_SetMinAndMax,
     SpinBtnPage_SetBase,
+    SpinBtnPage_SetIncrement,
     SpinBtnPage_CurValueText,
     SpinBtnPage_ValueText,
     SpinBtnPage_MinText,
     SpinBtnPage_MaxText,
     SpinBtnPage_BaseText,
+    SpinBtnPage_SetIncrementText,
     SpinBtnPage_SpinBtn,
     SpinBtnPage_SpinCtrl,
     SpinBtnPage_SpinCtrlDouble
@@ -103,7 +105,7 @@ protected:
     void OnButtonSetValue(wxCommandEvent& event);
     void OnButtonSetMinAndMax(wxCommandEvent& event);
     void OnButtonSetBase(wxCommandEvent& event);
-
+    void OnButtonSetIncrement(wxCommandEvent &event);
     void OnCheckOrRadioBox(wxCommandEvent& event);
 
     void OnSpinBtn(wxSpinEvent& event);
@@ -138,6 +140,9 @@ protected:
     // and numeric base
     int m_base;
 
+    // the increment
+    int m_increment;
+
     // the controls
     // ------------
 
@@ -159,7 +164,8 @@ protected:
     wxTextCtrl *m_textValue,
                *m_textMin,
                *m_textMax,
-               *m_textBase;
+               *m_textBase,
+               *m_textIncrement;
 
 private:
     wxDECLARE_EVENT_TABLE();
@@ -175,6 +181,7 @@ wxBEGIN_EVENT_TABLE(SpinBtnWidgetsPage, WidgetsPage)
     EVT_BUTTON(SpinBtnPage_SetValue, SpinBtnWidgetsPage::OnButtonSetValue)
     EVT_BUTTON(SpinBtnPage_SetMinAndMax, SpinBtnWidgetsPage::OnButtonSetMinAndMax)
     EVT_BUTTON(SpinBtnPage_SetBase, SpinBtnWidgetsPage::OnButtonSetBase)
+    EVT_BUTTON(SpinBtnPage_SetIncrement, SpinBtnWidgetsPage::OnButtonSetIncrement)
 
     EVT_UPDATE_UI(SpinBtnPage_SetValue, SpinBtnWidgetsPage::OnUpdateUIValueButton)
     EVT_UPDATE_UI(SpinBtnPage_SetMinAndMax, SpinBtnWidgetsPage::OnUpdateUIMinMaxButton)
@@ -227,12 +234,14 @@ SpinBtnWidgetsPage::SpinBtnWidgetsPage(WidgetsBookCtrl *book,
     m_textValue =
     m_textMin =
     m_textMax =
-    m_textBase = NULL;
+    m_textBase =
+    m_textIncrement = NULL;
 
     m_min = 0;
     m_max = 10;
 
     m_base = 10;
+    m_increment = 1;
 
     m_sizerSpin = NULL;
 }
@@ -311,6 +320,13 @@ void SpinBtnWidgetsPage::CreateContent()
     m_textBase->SetValue("10");
     sizerMiddle->Add(sizerRow, 0, wxALL | wxGROW, 5);
 
+    sizerRow = CreateSizerWithTextAndButton( SpinBtnPage_SetIncrement,
+                                             "Set Increment",
+                                             SpinBtnPage_SetIncrementText,
+                                             &m_textIncrement );
+    m_textIncrement->SetValue( "1" );
+    sizerMiddle->Add( sizerRow, 0, wxALL | wxGROW, 5 );
+
     // right pane
     wxSizer *sizerRight = new wxBoxSizer(wxVERTICAL);
     sizerRight->SetMinSize(150, 0);
@@ -481,6 +497,20 @@ void SpinBtnWidgetsPage::OnButtonSetBase(wxCommandEvent& WXUNUSED(event))
     m_sizerSpin->Layout();
 }
 
+void SpinBtnWidgetsPage::OnButtonSetIncrement(wxCommandEvent& WXUNUSED (event))
+{
+    int increment = wxAtoi( m_textIncrement->GetValue() );
+    if ( !increment )
+    {
+        wxLogWarning("Invalid increment value.");
+        return;
+    }
+
+    m_increment = increment;
+    m_spinctrl->SetIncrement(m_increment);
+    wxLogWarning("Setting increment to %d.", m_increment);
+}
+
 void SpinBtnWidgetsPage::OnButtonSetValue(wxCommandEvent& WXUNUSED(event))
 {
     if ( m_textValue->IsEmpty() )