OnActivate (C++)

Description

This example requires that a TApplicationEvents and a TListBox are on the form. Select the TApplicationEvents, double-click the OnActivate event, and add the following code to the handler. These events occur when the form gains or loses focus.

Code

void __fastcall TAppEventForm::ApplicationEventsActivate(TObject *Sender)
{
     lbOther->Items->Add("Event OnActivate");
}

void __fastcall TAppEventForm::ApplicationEventsDeactivate(TObject *Sender)
{
    lbOther->Items->Add("Event OnDeactivate");
}

Uses

• Vcl.AppEvnts.TCustomApplicationEvents.OnActivate ( fr | de | ja )
• Vcl.AppEvnts.TCustomApplicationEvents.OnDeactivate ( fr | de | ja )

Description

This example fills a list box with the names of TDataSources that are present and then fills a DBGrid on a second form with the data from the selected data source. The DBGrid is not filled in until Form2 is activated. Here is the code for Form1, which fills the list box.

Code

TForm1 *Form1;
TTable *Customers, *Blobs;
Boolean Form1Done = False;

void CreateCustSource()
{
  Customers = new TTable(Form1); // The owner will clean this up.
  Customers->Active = false; // The Table component must not be active.
  Customers->DatabaseName = "DBDEMOS";
  Customers->TableType = ttParadox;
  Customers->TableName = "CustInfo";
  Customers->Active = False;
  if (Customers->Exists) // Do not overwrite an existing table.
  {
	Customers->Close();
	Customers->DeleteTable();
  }
  // The Table component must not be active.
  // First, describe the type of table and give it a name.
  // Next, describe the fields in the table.
  Customers->FieldDefs->Clear();
  TFieldDef *pNewDef = Customers->FieldDefs->AddFieldDef();
  pNewDef->Name = "Field1";
  pNewDef->DataType = ftInteger;
  pNewDef->Required = true;
  pNewDef = Customers->FieldDefs->AddFieldDef();
  pNewDef->Name = "Field2";
  pNewDef->DataType = ftString;
  pNewDef->Size = 30;
  // Next, describe any indexes.
  Customers->IndexDefs->Clear();
  /* The first index has no name because it is a Paradox primary key. */
  Customers->IndexDefs->Add("","Field1", TIndexOptions() <<ixPrimary << ixUnique);
  Customers->IndexDefs->Add("Fld2Index","Field2", TIndexOptions() << ixCaseInsensitive);
  // Now that you have specified what you want, create the table.
  Customers->CreateTable();
  Customers->Active = True;
  for (int i = 1; i <= 20; i++)
	Customers->AppendRecord(ARRAYOFCONST((i*111, i*222)));
  Form1->CustomerDS->DataSet = Customers;
  Customers->Active = True;
}

void CreateBlobSource()
{
  int i;
  Blobs = new TTable(Form1);
  Blobs->DatabaseName = "DBDEMOS";
  Blobs->TableType = ttParadox;
  Blobs->TableName = "MyBlobInfo";
  Blobs->Active = False;
	// Do not overwrite an existing table.
//    if Blobs.Exists then
//      MessageDlg('CustInfo table already exists.', mtWarning, [mbOK], 0)
//    else
  if (Blobs->Exists)
  {
	Blobs->Close();
	Blobs->DeleteTable();
  };
  // The Table component must not be active. }
  // First, describe the type of table and give it a name. }
  // Next, describe the fields in the table. }
  Blobs->FieldDefs->Clear();
  TFieldDef *newDef = Blobs->FieldDefs->AddFieldDef();
  newDef->Name = "Field1";
  newDef->DataType = ftInteger;
  newDef->Required = True;
  newDef = Blobs->FieldDefs->AddFieldDef();
  newDef->Name = "Field2";
  newDef->DataType = ftBlob;
  newDef->Size = 30;
  // Next, describe any indexes. }
  Blobs->IndexDefs->Clear();
  // The first index has no name because it is a Paradox primary key. }
  TIndexDef *newIDef = Blobs->IndexDefs->AddIndexDef();
  newIDef->Name = "";
  newIDef->Fields = "Field1";
  newIDef->Options << ixPrimary;
/*
		with AddIndexDef do
        begin
          Name := 'Fld2Indx';
          Fields := 'Field2';
          Options := [ixCaseInsensitive];
        end;
*/
  // Call the CreateTable method to create the table. }
  Blobs->CreateTable();
  Blobs->Active = True;
  for (int i = 1; i <= 20; i++)
	Blobs->AppendRecord(ARRAYOFCONST((i*111, IntToStr(i*222))));
  Form1->BlobDS->DataSet = Blobs;
  Blobs->Active = True;
};


__fastcall TForm1::TForm1(TComponent* Owner)
  : TForm(Owner)
{
  CreateCustSource();
  CreateBlobSource();
  for (int i = 0; i < ComponentCount; i++)
  {
	if (Components[i]->ClassNameIs("TDataSource"))
	  ListBox1->Items->AddObject(Components[i]->Name,
		 dynamic_cast<TObject *>(Components[i]));
  }
}

void __fastcall TForm1::ListBox1MouseDown(TObject *Sender, TMouseButton Button, TShiftState Shift,
          int X, int Y)
{
  Form1Done = True;
}

Uses

• Vcl.Forms.TCustomForm.OnActivate ( fr | de | ja )
• System.Classes.TComponent.ComponentCount ( fr | de | ja )
• System.Classes.TComponent.Components ( fr | de | ja )