Size policy for ComboBoxes

COMBOBOX form items had a special behavior in previous versions because they adapted their size to the maximum item of the value list. On one hand, this is very convenient because the programmer doesn't have to find the biggest string in the value list, and to estimate how large it will be on the screen (with proportional fonts the string with the highest number of characters is not automatically the largest string). On the other hand, this behavior often led to an unpredictable layout if the programmer didn't reserve enough space for the COMBOBOX.

The SIZEPOLICY attribute gives better control of the result.

<G "Combo makes edit2 too big"                     >
 [edit1]
 [combo   ]
 [edit2   ]
... 
ATTRIBUTES 
EDIT edit1=formonly.edit1; 
COMBOBOX combo=formonly.combo,
   ITEMS=((0,"Veeeeeeeery Loooooooooooooooong Item"),(1,"hallo")),
   DEFAULT=0; 
EDIT edit2=formonly.edit2; 
END

Figure 1. Use of SIZEPOLICY

In this case, the "combo" field gets very large as does "edit2", because it ends in the same grid column. It will confuse the end user if he can input only eight characters and the field is apparently much bigger. Two possibilities exist to surround this:

Use an HBox to prevent the edit2 from growing, and use HBoxes for all fields which start together with combo and are as large or bigger than combo:

 <G "Edit2 in HBox doesn't grow" >
 [edit1]
 [combo  :]
 [edit2  :]
 ...

Figure 2. Use of HBox

Use the new SIZEPOLICY attribute, and set it to fixed to prevent combo from getting bigger than the initial six characters (6+Button):

 <G "Combo has a fixed size">
 ...
 [combo   ]
 [edit2   ]
 ... 
 ATTRIBUTES
 ...
 COMBOBOX combo=formonly.combo,
    ITEMS = ((0,"Veeeeeeeery Looooooooooooooooong Item"),(1,"hallo")),
    DEFAULT=0, SIZEPOLOCY=FIXED ;
....

Figure 3. Use of SIZEPOLICY as fixed

In this example the edit2 dictates the maximum size of combo, because even if the SIZEPOLICY is fixed, the elements are aligned by the Grid.

To prevent this and have exactly six characters (numbers) in the ComboBox, you need to de-couple combo from edit2 by using an HBox.

<G "Combo has a fixed size,sample 0,in HBox"
... 
Combo [combo  :]
Edit2 [edit2  :]
... 
COMBOBOX combo=formonly.combo,
   ITEMS = ((0,"12345678 Looooooooooooooooong Item"),(1,"hallo")),
   DEFAULT=0, SIZEPOLICY=FIXED, SAMPLE="0";

Figure 4. Use of HBox

Now the wanted six numbers are displayed and combo does not grow to the size of edit2.