vania@osf.ORG (Vania Joloboff) (06/12/90)
There has been a number of questions on the net concerning the Form widget. We expect the following guidelines, which will be added to 1.1 documentation, will help XmForm users. 1. Every child should have an attachment either on the left or the right. If initialization or XtSetValues leaves a widget without such an attachment, the result depends upon the value of XmNrubberPositioning. If XmNrubberPositioning is false, it is given an XmNleftAttchment of XmATTACH_FORM, and an XmNleftOffset equal to its current x value. If XmNrubberPositioning is true, it is given an XmNleftAttachment of XmATTACH_POSITION, with an XmNleftPosition that corresponds to the percentage of its x value relative to the width of the form. In either case, if the child has not been previously given an x value, its x value will be taken to be 0, which will place it at the left side of the form. 2. If you want to create a child without any attachments, and then later (e.g. after creating and managing it, but before realizing it), give it a right attachment via XtSetValues, rememeber to set its XmNleftAttachment to XmATTACH_NONE at the same time (because in previous step, it may have been defaulted to left). 3. The XmNresizable resource controls only whether a geometry request by the child will be granted. It has no effect on whether the child's size can be changed because of changes in geometry of the form or of other children. 4. If a child has attachments on both the left and the right sides, its size is completely controlled by the form. It can be shrunk below its minimum size, and geometry requests to change its width may be refused. 5. If a child has attachments on only its left or right side, it will stay at its preferred width. This may cause it to be clipped by the form or by other children. 6. If a child's left (or right) attachment is set to XmATTACH_SELF, the attachment is converted to an attachment of XmATTACH_POSITION, with a position that corresponds to x value of its left (or right) edge. To fix the position of a side at a specific x use XmATTACH_FORM (or XmATTACH_OPPOSITE_FORM) with the x value as the left (or right) offset. 7. Unmapping a child has no effect on the form except that the child is not mapped. 8. Unmanaging a child unmaps it. If no other child is attached to it, or if all children attached to it, and all children recursively attached to them are also all unmanaged, then all of those children are treated as if they did not exist in determining the size of the form. 9. To change the x value of a child you should simultaneously set its left attachment to either XmATTACH_SELF or XmATTACH_NONE. Otherwise, the request may not be granted. If resizable is false, the request will only be granted if the child's size can remain the same. All of the above is true of top and bottom attachments as well with top acting like left and bottom acting like right.