Custom Server Controls

Re: EnsureChildControls?

Brijesh50 — Fri, 26 Jun 2009 19:54:17 GMT

While reading an article on MSN for creating Custom Templated Control, the override method for DataBind calls CreateChildControls as follows

protected override CreateChildControls()

{

//Logic for creating TemplateContainer

//Logic for calling ITemplate.InstantiateIn()

//Logic for adding TemplateContainer to Controls Collection.

}

protected override DataBind()

{

CreateChildControls();

ChildControlsCreated = true;

base.DataBind();

}

Another book I was reading did have the same logic for CreateChildControls but on databind does the following

protected override DataBind()

{

EnusreChildControls();

base.DataBind();

}

I am confused as to whats the recommended practise?

Please Advise

Thanks

Brijesh

Re: EnsureChildControls?

scobrown — Tue, 24 Apr 2007 21:39:25 GMT

I guess the short and sweet answer is that CreateChildControls() is not called by the constructor.

Re: EnsureChildControls?

scobrown — Tue, 24 Apr 2007 21:36:01 GMT

Simple example: Lets say you have class FooObject with a string property Bar, and the following property Foo in your Control: 
 
private FooObject _foo;
public string Foo
{
    get
    {
        return _foo.Bar;
    }
    set
    {
        _foo.Bar = value;
    }
}

If you initialize _foo in CreateChildControls, then this code could throw a null reference error. The problem would occur if you try to set the value of Foo in the Designer:

Properties set in the Designer will be set at runtime before any calls to CreateChildControls. You could get lucky if some other property gets set before yours and it calls CreateChildControls. Imagine the .net runtime making the following series of call based on the above:

YourControl newControl = new YourControl();
newControl.Foo = "This will cause a null reference";
ParentControl.Controls.Add(newControl);

Anytime you are initializing an object in CreateChildControls, you should wrap it's property accessor with EnsureChildControls. Even if you do the following:

private FooObject _foo = new FooObject();
public string Foo
{
    get
    {
        return _foo.Bar;
    }
    set
    {
        _foo.Bar = value;
    }
}

If you set _foo to a new value in CreateChildControls(), the new value will have the default Bar value and not the new one. When creating a control, most properties you expose will operate on private variables whose value will be set in CreateChildControls(), so you should always add the EnsureChildControls.

EnsureChildControls?

nisarkhan — Tue, 24 Apr 2007 15:02:40 GMT

Could somebody give me a better feel for the why's and when's of EnsureChildControls?

I understand what it does ( calls CreateChildControls if needed ) , but I don't get when or why I would call it.

what's the senario?

Thanks