Waiting for Controls to be Initialized

My form looks something like a three-pane email client. Left side is a grid with a list of people. Top right is the current person's detail record. Bottom right is a custom control with many checkboxes displaying the current person's areas of expertise:

[x] cooking [x] window cleaning [x] brain surgery

[x] massage-therapy [x] singing [ ] random acts of vandalism

When the form is opened, the focus goes to the first person listed in the grid on the left-side of the form,, and the grid's focused_row_changed event fires. In the handler for this event I get the current person's id, then fetch detail data for that person from the database and populate the detail record, and also fetch the person's areas-of-expertise rows and set the checkboxes. All of this is working fine except when the form is first opened, because then the custom control with its many checkboxes is not yet initialized.开发者_高级运维 At that point MyCustomControl is null.

if (null != MyCustomControl)
{
  MyCustomControl.SetCheckedValues( datasource);
}

What is the best practice design-pattern for handling this situation? What do I do here when my control isn't fully initialized yet?

if (null != MyCustomControl)
{
  MyCustomControl.SetCheckedValues( datasource);
} 
else 
{
  // ?? Wait around for a bit and keep trying every 100ms?
}

The way I have solved this in my controls when they have had this problem is to implement ISupportInitialize.

In your control, you would put something like:

public class MyCustomControl: ISupportInitialize
{
    private bool _initializing = false;

    private void BeginInit()
    {
        _initializing = true;
    }

    private void EndInit()
    {
        _initializing = false;
    }

    private void SomeMethodThatWouldRaiseAnEventDuringInit()
    {
        if (_initializing) return;
        //...
    }
}

The windows forms designer checks for your control implementing the interface, and produces this code in the .Designer.cs file:

((System.ComponentModel.ISupportInitialize)(this.customControl1)).BeginInit();
///
/// customControl1
///
this.customControl1.SelectedIndex = 0;  //this would normally raise the event
((System.ComponentModel.ISupportInitialize)(this.customControl1)).EndInit();

From what I understand, you are setting MyCustomControl.SetCheckedValues( datasource); when focused_row_changed event fires.

This also tends to happen when the form is just loading, which is generally not desired, because you end up with events telling things to load when, for example, a selected index is still -1.

The way I have been working around this is I have a global boolean in the form called doneLoading. It starts off false and becomes true when the Form_Shown() event gets called.

From there I just put an if(doneLoading) around any piece of code that needs to wait until the form is actually done loading before it is allowed to execute. In your case, I would do:

if(doneLoading)
{
MyCustomControl.SetCheckedValues( datasource);
}

Do your UI initialization functions in a subroutine that isn't called until after all the other UI elements are initialized, or base your calculations on the back-end values instead of the UI.

in response to comments and other posts, if you can't get anything else to work, you can add a 'refresh' button to the UI