Why does this work and this doesn't?
public Form1()
{
InitializeComponent();
comboBox1.DisplayMember = "Name";
comboBox1.ValueMember = "ID";
LoadUsersToComboBox();
}
PersonRepository peopleRepo = new PersonRepository();
private void LoadUsersToComboBox()
{
comboBox1.DataSource = peopleRepo.FindAllPeople().ToList();
}
private void button2_Click(object sender, EventArgs e)
{
LoadUsersToComboBox();
}
This method will load a comboBox with value only on the FIRST time, but not on subsequent attempts:
private void LoadUsersToComboBox()
{
comboBox1.DataSource = peopleRepo.FindAllPeople(); /*Return IQueryable<Person>*/
}
And this loads every time I call LoadUsersToComboBox():
private void LoadUsersToComboBox()
{
comboBox1.DataSource = peopleRepo.FindAllPeople().ToList();
}
Why does the first one only load the 开发者_JAVA百科first time?
Here is the code to the PeopleRepository class:
namespace SQLite_Testing_Grounds
{
public class PersonRepository
{
private ScansEntities3 db = new ScansEntities3();
public IQueryable<Person> FindAllPeople()
{
return db.People;
}
}
}
Solution is simple :
// This method returns the same reference every time
public IQueryable<Person> FindAllPeople()
{
return db.People;
}
As a result :
// Nothing changes, DataSource old value is still the same (same reference,
// even is the content of the People list does change).
comboBox1.DataSource = peopleRepo.FindAllPeople();
// ToList() creates a new object each time, so DataSource is assigned to a
// NEW object, and so calls a kind of invalidation of its visual.
comboBox1.DataSource = peopleRepo.FindAllPeople().ToList();
.
That's a data-binding basics, actually I'm not at all a WinForms guy (I know a lot more about WPF), but I think that internally, you have someting similar than :
private object dataSource;
public object DataSource {
get {
if (value != dataSource) {
dataSource = value;
RaisePropertyChanged("DataSource");
}
}
}
In this call, you are setting the datasource, but not the databind call to actually bind the data. Can you post the method where you call .databind?
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