Check-in [e531f63c61]

A **frame** keeping a size without reason just feels like a bug and mostly leads to unwanted results.

Mostly, it looks just ugly, but there are critical use-cases, specially in scrolled frames.

When the BWidget autoscroll package is used, which displays scrollbars on demand, the scrollbars do not disappear if the contents is gone.
And there is nothing, a programmer can do, as the Configure event does not fire on the scrolled frame widget.

Another example is the scrolledwindow example by Emiliano in ticket 2863003fff <https://core.tcl.tk/tk/info/12006979562649c9> , where the solution 2 specific part may be removed \(or is ignored\).

A typical workaround is to configure the width/height manually after the last children was unmapped.
Unfortunately, this fact may not be determined for example by scrolling widgets etc. An eventual Configure binding is not firing.

Within this TIP, a new virtual event `<<NoManagedChild>>` is fired to inform about no remaining childs.

# Example
................................................................................
	requested frame height: 100

Technically, the frame ".c.f.i1" was packed into the client frame ".c.f".
The client frame ".c.f" changes its requested size to hold the new child, which invokes the Convigure event and adjustes the scrolling region of the canvas.
The new scrolling region is shown graphically by the scrollbar.

Then press the "-" button to remove the user widget. The console output is:
	-


So, the child widget ".c.f.i1" is destroyed, but the frame ".c.f" does not rechange its requested size to 1x1 \(initial value\) but stays at 100x100 showing an empty plane.
The scrollbar is not updated and the megawidget has no possibility to adjust that \(expect additional user action to inform that the last child was removed\).

One may also try to add two childs and to remove them. It gets clear, that the widget is resized on removel if it is not the last widget.

With the proposed patch applied, an additional event is fired the removal of the last widget would restore the initial frame size of 1x1 which would invoke the Configure event and the scrollbar would be adjusted.

................................................................................
	    .c.f configure -height 1
	    .c.f configure -height 0
        }
	bind .c.f <<NoManagedChild>> frameNoChild

# Reference Implementation

Emiliano has provided a ticket 2863003fff <https://core.tcl.tk/tk/info/2863003fff>  with the implementation in branch bug-d6b95ce492 <https://core.tcl.tk/tk/timeline?r=bug-d6b95ce492&nd&c=2016-09-21+06%3A32%3A55&n=200>.

This solution is now continued with the tag "tip518-event-last-child-unmanaged".

Koen Dankart and Francois Vogel have worked on the solution of the similar tip474, which is available in branch bug-d6b95ce492-alt: <http://core.tcl.tk/tk/timeline?r=bug-d6b95ce492-alt&nd&c=2016-09-22+09%3A16%3A21&n=200> .
This information may eventually also be relevant.

# Rejected Proposal

TIP 454 <https://core.tcl.tk/tips/doc/trunk/tip/454.md> has proposed to set the size of the widget automatically to 1x1 (the initial size if no widget packed/gridded).

Please read the discussion within the TIP which led to withdraw the proposal.

# Discussion

## Why not use the event name \<\<Configure\>\> ?

................................................................................

To invoke `<<Configure>>` instead `<<NoManagedChild>>` would trigger incompatibility 2 of TIP454.
Due to that, a new virtual event is proposed.

# Copyright

This document has been placed in the public domain.

A **frame** keeping a size without reason just feels like a bug and mostly leads to unwanted results.

Mostly, it looks just ugly, but there are critical use-cases, specially in scrolled frames.

When the BWidget autoscroll package is used, which displays scrollbars on demand, the scrollbars do not disappear if the contents is gone.
And there is nothing, a programmer can do, as the Configure event does not fire on the scrolled frame widget.

Another example is the scrolledwindow example by Emiliano in [ticket 2863003fff](https://core.tcl.tk/tk/info/12006979562649c9), where the solution 2 specific part may be removed \(or is ignored\).

A typical workaround is to configure the width/height manually after the last children was unmapped.
Unfortunately, this fact may not be determined for example by scrolling widgets etc. An eventual Configure binding is not firing.

Within this TIP, a new virtual event `<<NoManagedChild>>` is fired to inform about no remaining childs.

# Example
................................................................................
	requested frame height: 100

Technically, the frame ".c.f.i1" was packed into the client frame ".c.f".
The client frame ".c.f" changes its requested size to hold the new child, which invokes the Convigure event and adjustes the scrolling region of the canvas.
The new scrolling region is shown graphically by the scrollbar.

Then press the "-" button to remove the user widget. The console output is:

	-

So, the child widget ".c.f.i1" is destroyed, but the frame ".c.f" does not rechange its requested size to 1x1 \(initial value\) but stays at 100x100 showing an empty plane.
The scrollbar is not updated and the megawidget has no possibility to adjust that \(expect additional user action to inform that the last child was removed\).

One may also try to add two childs and to remove them. It gets clear, that the widget is resized on removel if it is not the last widget.

With the proposed patch applied, an additional event is fired the removal of the last widget would restore the initial frame size of 1x1 which would invoke the Configure event and the scrollbar would be adjusted.

................................................................................
	    .c.f configure -height 1
	    .c.f configure -height 0
        }
	bind .c.f <<NoManagedChild>> frameNoChild

# Reference Implementation

Emiliano has provided a [ticket 2863003fff](https://core.tcl.tk/tk/info/2863003fff) with the implementation in [branch bug-d6b95ce492](https://core.tcl.tk/tk/timeline?r=bug-d6b95ce492&nd&c=2016-09-21+06%3A32%3A55&n=200).

This solution is now continued with the tag "tip518-event-last-child-unmanaged".

Koen Dankart and Francois Vogel have worked on the solution of the similar tip474, which is available in [branch bug-d6b95ce492-alt](http://core.tcl.tk/tk/timeline?r=bug-d6b95ce492-alt&nd&c=2016-09-22+09%3A16%3A21&n=200).
This information may eventually also be relevant.

# Rejected Proposal

[TIP 454](454.md) has proposed to set the size of the widget automatically to 1x1 (the initial size if no widget packed/gridded).

Please read the discussion within the TIP which led to withdraw the proposal.

# Discussion

## Why not use the event name \<\<Configure\>\> ?

................................................................................

To invoke `<<Configure>>` instead `<<NoManagedChild>>` would trigger incompatibility 2 of TIP454.
Due to that, a new virtual event is proposed.

# Copyright

This document has been placed in the public domain.