组合框参数在德尔福

Question

没有默认值

我工作的程序使用if语句添加一行到SQL的另一个组合框

procedure TFmNewGarage.ComboBoxCountryEnter(Sender: TObject); 
begin 
    ADOQueryCountry.SQL.Clear; 
    ADOQueryCountry.SQL.Add('SELECT DISTINCT Country'); 
    ADOQueryCountry.SQL.Add(' FROM TblBaseCar'); 
    ADOQueryCountry.Open; 
    while not ADOQueryCountry.Eof do 
    begin 
    ComboBoxCountry.Items.Add(ADOQueryCountry['Country']); 
    ADOQueryCountry.Next; 
    end; 
end; 

procedure TFmNewGarage.ComboBoxCountryChange(Sender: TObject); 
begin 
    SelA:=True; 
    ComboBoxManufacturer.Show; 
    ComboBoxCountry.Hide; 
end; 

procedure TFmNewGarage.ComboBoxManufacturerEnter(Sender: TObject); 
begin 
    ADOQueryManufacturer.SQL.Clear; 
    ADOQueryManufacturer.SQL.Add('SELECT DISTINCT Manufacturer'); 
    ADOQueryManufacturer.SQL.Add(' FROM TblBaseCar'); 
    if SelA=true then 
    ADOQueryManufacturer.SQL.Add(' WHERE Country=(ComboBoxCountry.seltext)'); 
    ADOQueryManufacturer.Open; 
    while not ADOQueryManufacturer.Eof do 
    begin 
    ComboBoxManufacturer.Items.Add(ADOQueryManufacturer['Manufacturer']); 
    ADOQueryManufacturer.Next; 
    end; 
end; 

的内容在运行时，这导致错误ComboBoxCountry.seltext没有默认值，任何人都可以帮我纠正这个问题吗？

Answer 1

SelText是不是你应该使用的财产。您需要为选择ItemIndex组合框Items值：

var 
Country: string; 
begin 
    ... 
    if ComboBoxCountry.ItemIndex <> -1 then 
    begin 
    Country := ComboBoxCountryItems[ComboBoxCountry.ItemIndex]; 
    ADOQueryManufacturer.SQL.Add('WHERE Country = ' + QuotedStr(Country)); 
    end; 
end;