Creating child controls

When a control creates another control (for performing some task), the other control is usually a “child control” (although TvControls does not enforce that). Usually the AddAsChild method is used to add the new control.

You can add a child control whenever you need, but there are some important things to keep in mind. Let’s see them all :)

Creating the child control

To add a child control you need a reference to the components tree. You can obtain this reference through the OnControlMounted method:

private IComponentTree _componentTree;
protected override void OnControlMounted(ITuiEngine engine)
{
    _componentTree = engine.UI;
}

When you need you can use the AddAsChild method. The following control adds the menu control:

 _componentTree.AddAsChild(menu, this);

Important! Remember that adding a component (thus adding a control too) is an asynchronous operation!

You can add a child control before adding the parent control, but in this case adding the child control will be deferred until the parent is added.

Setting the focus to a newly created component

There are several ways to do it. But, as adding a control is an asynchronous operation, the most obvious way to create a control and set the focus to it, do NOT work:

 _componentTree.AddAsChild(menu, this);
 menu.Metadata.Focus(); // probably won't work because menu could not be added yet!

You need to ensure that the component is created before setting the focus. A simple way is to add the OnComponentMounted event to the child control to focus the control when added:

_list = new TvList<MenuEntry>(builder);
_list.AsComponent()
    .Metadata.OnComponentMounted
    .AddOnce(ctx =>
    {
        _list.Metadata.Focus();
        // Can use also: ctx.ControlMetadata().Focus() if not reference to control is available
    });

Capturing the focus

A control can capture the focus. When the focus is captured only itself and their descendants can be focused. A typical example of capturing the focus is creating a Dialog. When the dialog is shown, you want to iterate only over the controls of the dialog.

A control can capture the focus by calling CaptureFocus() from its Metadata property.

CaptureFocus do not perform any focus change. If the focus is set to a control that is not descendant of the control that captured the focus, this control will be focused after calling CaptureFocus. However when the focus changes for any reason (like user pressing TAB) only the control that called CaptureFocus and its descendants could be focused.

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