在验证文本框/复选框之前，文本框/复选框的数据绑定值不正确

Question

I have a winforms checkbox that is bound to a property of an Entity Framework entity.

So for example, I have bindingSource.DataSource = myDog with a checkbox bound to the property IsSleeping , so that when the user checks the box, IsSleeping becomes true, and when the user unchecks the box, IsSleeping becomes false.

This works fine. The problem is that the value of IsSleeping is not updated until the checkbox is validated, which only occurs when focus moves away from the checkbox to something else. Thus, if I want something to happen when the box is unchecked:

private void IsSleepingCheckbox_CheckedChanged(object sender, EventArgs e)
{
    OnDogPropertyChanged(myDog);
    MyAnimalEntities.SaveChanges();
}

myDog.IsSleeping will still be true, until the checkbox's Validated is later raised. Thus, when poor myNaughtyKitty (who is listening to the DogPropertyChanged event) comes to eat out of myDog 's food dish thinking myDog is sleeping, myDog is really just waking up! Oh no!

Even worse , MyAnimalEntities.SaveChanges() does not see the changes to myDog yet, so the value of IsSleeping is never saved to the database. Moving the .SaveChanges() call to IsSleepingCheckbox_Validated does not solve this problem, because if the checkbox is toggled but then the form is closed without ever moving focus away from the checkbox, the checkbox is never validated and thus its state is never saved!

I imagine this must be a fairly common problem with databinding and checkboxes/textboxes, and indeed I've found a ton of posts on the subject online, but no one ever seems to have a solution. Has anyone been able to find a workaround for this?

Answer 1

You can change the Binding.DataSourceUpdateMode property to OnPropertyChanged (the default is OnValidation ), which will cause the data source to be updated when the user clicks the checkbox. Unfortunately, the CheckedChanged event still fires before the data source is updated.

To deal with this, you can handle the BindingSource.ListChanged event and move your SaveChanges code there.

bindingSource = new BindingSource();
bindingSource.DataSource = myDog;
checkBox1.DataBindings.Add(new Binding("Checked", bindingSource, "IsSleeping"));
checkBox1.DataBindings[0].DataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged;

bindingSource.ListChanged += new ListChangedEventHandler(bindingSource_ListChanged);

HTH

Answer 2

This is the appropriate way to make this work. Handle the CheckBox Validated Event

    /// <summary>
    /// Handles Check Box State if Changed
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void checkBoxBidSummaryItem_Validated(object sender, EventArgs e)
    {
        // Code to execute...
        _MyEntity.Save(_businessObject.SelectedBid);
    }