C# Database: combobox value base on another combobox. How?

Fahad Aldaferi

I have an application that display some info from access 2016 database. - Form2 will display data from studentInfo table so Form2 will contain studentIDTextBox, studentNameComboBox, classComboBox, levelComboBox, studentDateDateTimePicker, nationalityComboBox, cityComboBox, provinceComboBox, blockTextBox...etc

levelComboBox:

SelectedValue: studentInfoBindingSource - Level
DataSource: studentLevelBindingSource
DisplayMember: Level
ValueMember: LevelID

classComboBox:

SelectedValue: studentInfoBindingSource - Class
DataSource: studentClassBindingSource
DisplayMember: Class
ValueMember: ClassID

Now my question is: Without effect the info has been display i want if i add a new item ( record ) to the database and when i choice a specific Level from levelComboBox it will change a list of classes within the selected Level in classComboBox and vice versa. How i can do that ?

I try to do that by using the code below but it is not good:

private void provinceComboBox_SelectedIndexChanged(object sender, EventArgs e)
{
var cityQuary =
from displayCity in student1516DataSet.city
where displayCity.ProvinceName == provinceComboBox.Text
select displayCity;
cityComboBox.DataSource = cityQuary.AsDataView();
}

7 Replies

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Hanif Hefaz10y ago
That great, it worked. by the way i just taught it may be related with references.
Fahad Aldaferi10y ago
HiHanif Hefaz, I think it is not related to references you just said
Hanif Hefaz10y ago
Have you used assembly references? try something like this
using.system.configuration
or google the related reference i think
Fahad Aldaferi10y ago
I have question How i can do the vice versa. Now i have a previous code which work fine with a little change on it like the code below so i want the user when he choice the city the app will directly assign the right Province only if provinceComboBox is empty.
private void provinceComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            if ( provinceComboBox.SelectedIndex != -1  )
            {
                var cityQuary =
                    from displayCity in student1516DataSet.city
                    where displayCity.ProvinceName == provinceComboBox.SelectedValue.ToString()
                    select displayCity;

                cityComboBox.DataSource = cityQuary.AsDataView();
            }
        }
I try this code with cityComboBox but it display some errors says "
An exception of type 'System.NullReferenceException' occurred in schoolManagments.exe but was not handled in user code
Additional information: Object reference not set to an instance of an object.
"
private void cityComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (provinceComboBox.SelectedIndex == -1)
            {
                var proviceQuary =
                    from displayProvice in student1516DataSet.city
                    where displayProvice.CityID == cityComboBox.SelectedValue.ToString()
                    select displayProvice;

                provinceComboBox.DataSource = proviceQuary.AsDataView();
            }
        }
Fahad Aldaferi10y ago
ThanksHanif Hefaz & Karthik Elumalai. Now the code work fine :)
privatevoidprovinceComboBox_SelectedIndexChanged(objectsender,EventArgse)
{
if(provinceComboBox.SelectedIndex>-1)
{
varcityQuary=
fromdisplayCityinstudent1516DataSet.city
wheredisplayCity.ProvinceName==provinceComboBox.SelectedValue.ToString()
selectdisplayCity;
cityComboBox.DataSource=cityQuary.AsDataView();
}
}
Karthik Elumalai10y ago
Hi fahad aldaferi,
I have personally posted the code snippet for select the dropdown values based on the other dropdown with simple example below.
http://www.c-sharpcorner.com/code/3066/simple-web-service-method-for-generating-country-state-and-city-in-dropdo.aspx
You can slightly change the as per your requirement and it will work fine.Hope it will be helpful ,kindly let me know your thoughts
thanks
karthik
Hanif Hefaz10y ago
follow these links i found them useful.
1-https://www.youtube.com/watch?v=rdAqkg6bGT0
2-https://www.youtube.com/watch?v=I_wwlZofCgk
3-https://www.safaribooksonline.com/library/view/.../ch01s03.html
4-www.c-sharpcorner.com/uploadfile/mahesh/combobox-in-C-Sharp/
5-www.c-sharpcorner.com/forums/get-a-combobox-value-from-one-from-to-other-form
Hope this will help you.