組合框參數在德爾福

Question

沒有默認值

我工作的程序使用if語句添加一行到SQL的另一個組合框

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; 

的內容在運行時，這導致錯誤ComboBoxCountry.seltext沒有默認值，任何人都可以幫我糾正這個問題嗎？

Answer 1

SelText是不是你應該使用的財產。您需要爲選擇ItemIndex組合框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;