How-to-fill-a-ComboBox-with-Table-values


            Title: How to fill a ComboBox with Table-values.
Question: You will filter a Table with values from it own columns.
Answer:
Create Form1 with this Objects
 Table1 Table with Customer-Infos e.g.
 Firstname
 ....
 Month (string yyyymm with Secondary Index)
 ....
 DataSource1
 DBGrid1
 ComboBox1
 This procedure fills the Combobox with values from field Month.
 Your Table can have many Records with the sam value:
 200106
 200108
 200108
 200109
 200109
 200110
 ... and so on
 In the Combobox is only one Entry from every value stored:
 200106
 200108
 200109
 200110
 If you select one of this Entries, the Table ist filtered
 with this value
 private
 cFilter: string;
procedure TForm1.FillCombo;
var
 cMonth: string;
begin
 MtCombo.Items.clear;
 Table1.Filter := 'Month ''000000''';
 // first add one entry for select to 'Filter-Reset'
 MtCombo.Items.append('');
 Table1.open;
 // set the Month-Compare-value
 cMonth := '';
 // go thru the Table and get the values
 // for every existing value is only one loop produced
 // Missing values are ignored.
 // at start cMonth is empty and all Records are available.
 while not Table1.Eof do begin
 // Now add the Month-value from the first Record of 
 // this filter-set to the Combobox 
 MtCombo.Items.append(Table1['Monat']);
 // create the Month-Filter to Greater-Than-Current-Month
 cFilter := 'Month ''' + Table1['Month'] + '''';
 // save the Current Month for using after the last loop
 cMonth := Table1['Month'];
 // set the filter for the next loop now
 Table1.Filter := cFilter;
 end;
 // Select the first Combobox-Entry
 MtCombo.ItemIndex := MtCombo.Items.Count - 1;
 MtCombo.Text := cMonth;
 // and set the selectet value as filter
 Table1.filter := 'Month = ''' + MtCombo.Items[MtCombo.ItemIndex] + '''';
 cFilter := Table1.filter;
 Table1.first;
end;
// at Startup the Combobox is filled first
procedure TForm1.FormCreate(Sender: TObject);
begin
 FillCombo;
end;
// in the Combobox onChange event set the Table-Filter 
procedure TForm1.MtComboChange(Sender: TObject);
begin
 // look if currently filter is not ''
 // than create this value as an filter-expression
 if (MtCombo.Items[MtCombo.ItemIndex] '') then 
 Table1.filter := 'Month = ''' + MtCombo.Items[MtCombo.ItemIndex] + ''''
 else 
 // otherwise reset filter-expression because '' is selected
 Table1.Filter := '';
 Table1.Last;
 // save the last Filter-Settings
 cFilter := Table1.Filter;
end;
// if you produces new records with insert or append
// your field Month is also set to an new value (by
// your self). If this value other than the stored
// values in the Combobox, then you can call FillCombo
// to create the new Combobox-entries:
procedure TForm1.Table1AfterInsert(DataSet: TDataSet);
begin
 ...
 FillCombo;
end;
Regards
Kurt
VCL Delphi
