# VFAQ (V COMMAND CONTROLS)

- How to dynamically modify list controls
- Does V have Text Edit controls?
- Changing size of dialogs
- History of values on menus
- Getting dynamic changes from TextIn Controls
- Grouping controls in a dialog
- Layout of Controls different in X and Windows
- vIcons as controls in a vCanvasPane
- Controlling width of Lists
- Waiting for computations

## How to dynamically modify list controls

Q:
  I need the ability to dynamically add/delete/modify items in a list box control.

  A:

  There are two ways to do this. You can modify the contents of the ORIGINAL list, and then call the SetValue function with the 'ChangeList' value. You can also create a new list, and call SetValue with the 'ChangeListPtr' value. These are explained in the reference manual in more detail.

  ## Does V have Text Edit controls?

  Q:
  Are there any text editors (or a text widget) out there written using V?

  A:

  V currently has a relatively complete text editor class. It will support standard keypad commands for standard line-oriented text. You can extend the command set of the editor, and it handles buffering for reasonably sized files. It can be extended to handle unlimited file sizes.

  ## Changing size of dialogs

  Q:
  With dialogs, and even command windows is there a way to set the minimum and/or maximum size allowed for the user to resize? Some dialogs just don't make any sense to allow the user to resize, while others would be really nice to allow the user to change the size on.

  A:

  Dialogs are whatever size they are. The X window manager does whatever it does to dialogs if you fiddle them, and I don't think I can fix V to freeze the sizes.

  ## History of values on menus

  Q:
  I have a field that I would like to maintain a ``history'' of, such that if the user enters a new value it will be added the the history. Something of a combination C_ComboBox and a C_TextIn. I'm certain you've seen this sort of thing under Windoze.

  A:

  Hmm... V does not allow you to dynamically add items to a menu. It does let you change the contents of a menu item. A good compromise might be to keep a history of the last 4 things in a menu (using blanks or until you fill in the field), and the full history in a dialog using a list or a combo box (which can now be totally dynamic in V 1.10).

  ## Getting dynamic changes from TextIn Controls

  Q:
  Upon completion of data entry into a single line text field, is there a way to retrieve the data from that field upon completion of text entry(signaled either by a carriage return or a tab key) rather than pressing a button to invoke the GetTextIn function?

  A:

  V can't do this. You could do this directly on X or on Windows, but the mechanism is completely different on each platform, so V has to hide it. On windows, pressing Return will terminate the dialog if there is a default button defined, but that helps only for one text in field, and it doesn't work on the X version. The next best alternative might be to put a "submit" button to the right of each field you want to work this way. A pain, but...

  Q:

  Is there a way to traverse a set of single line text fields per keystroke, as opposed to moving the mouse from one text field to another?

  A:

  This works on the Windows version right now, but doesn't work on the X Athena version. It might work for the Motif version when it is done.

  ## Grouping controls in a dialog

  Q:
  When designing a dialog window, I sometimes want to place a control to the right of several other controls. This can be done by giving cRightOf and cBelow (members of CommandObject) the right values. By this I can place a control to the right of another. I would like to place the control to the right of three other controls but as the size becomes dynamic, I don't know which one will be the largest. Is there a way to express this in the CommandObject structure? Or are there other ways to achieve this goal?

  A:

  The best way I know to get a control to the right of (or below or whatever) a group of other controls is to place the other controls in a frame. Since you can make the frame have no border, you can make it so it won't show on the displayed dialog. You can also use blank objects as space fillers to help control positions. Another thing that helps is padding the messages with blanks to get alignment right.

  Another trick is to make a control that will be as large as the largest control that gets generated, and then make it hidden. It will count in the size calculations, but not be displayed in the dialog. Hidden controls can occupy the same location on the dialog as the controls you want to see.

  Using borderless frames is the best tool that V has for controlling tricky layout, but even so, sometimes you still can't get everything placed exactly as you want. This is one of the compromises of the V design. Most of the time, you can design pretty good looking dialogs. Sometimes, you have to compromise, and get OK instead of perfect. All things considered, I hope most V users will find this a reasonable compromise.

  ## Layout of Controls different in X and Windows

  Q:
  I've got a problem with positioning the controls in a dialog box. The Linux version is working correct, but the same source, compiled with Borland, results in a dialog box with overlapping controls. Do you have a clue?

  A:

  The documentation needs to be more explicit about this. It turns out that this is actually an inherent problem with V. If you had started out with Windows, you'd probably find the X version was OK. The problem is that not all controls are the same relative size on X and Windows. While dialogs with just buttons and label fields will generally work on both platforms, using lists, spinners, or progress bars will often give a good looking result on one platform, but not another.

  Fortunately, there are a couple of solutions for this problem. Both, however, involve being able to compile for both platforms. Of course, you wouldn't be seeing the problem at all if you weren't compiling on both platforms.

  Sometimes using a different control as the reference control works. For example, if you had a label and a spinner on one line, and want to put another label and spinner below, the natural tendency is to use the label since it is first. However, the spinner is taller on Windows, so will generate an overlap on the Windows version. Using the spinner as the reference rather than the label solves the problem.

  The other thing is to use borderless frames, and position controls relative to the frame rather than controls in the frame. By combining this and the above technique, you can usually design an attractive dialog that works on both platforms. The vDraw example program quick pick dialog uses these tricks to get a layout suitable for both platforms.

  I wish it were easier, but it is just not possible to get all controls the same relative size on all platforms. At least there is a way around the problem, even if it takes a bit more care. Usually, though, it just takes 20 or 30 minutes to clean up a dialog.

  ## vIcons as controls in a vCanvasPane

  Q:
  I'm working on a simple application for FreeBSD, and would like to use the V GUI toolkit. I have the following need for this application:

  The main window of the application will represent a group of objects as icons. Each icon will have an image and a name. When the user double-clicks on an icon, a dialog allowing the user to customize that object will be created/shown.

  Is there a straight forward method in V to represent a scrolling "icon arena", where each icon represents an object? I've thought about making each object and icon button and just adding all of them to a command window, but I don't quite see how to make the window scrollable.

  A:

  You will have to do some work, but this would be true for most any GUI toolkit.

  You can draw a V icon anywhere in the canvas of a command window. For each icon, you would have to track its X,Y position, and associated label. (A simple list would do.) You then map mouse clicks to the icon you've placed at the mouse location by searching your list. Use scroll bars in the canvas as needed, and adjust mouse coordinates to account for scrolling.

  A little work, but not that hard. The double click is harder. V does not support a separate message for double clicks. You can fake it by counting two clicks, or get close to real by using a timer. This limitation is mostly due to the Athena widget set on X.

  ## Controlling width of Lists

  Q:
  One more question, have you thought about my suggestion to let the user control the width of a C_List ?

  A:

  The way lists are supposed to work now is that V will use the width of the widest item in the list when first instantiated. So one possibility is to first create the list with a fake item that is as wide as the widest list item you expect, and then use ChangeList or ChangeListPtr to change to the actual list. The problem on Windows is that it is hard to dynamically resize the whole dialog, so I do the best I can by sizing the list to the widest item. This then determines the size and positions of all the other controls in a dialog with a list. In fact, I don't know how non-V Windows programs handle list size, if they really do. Windows dialogs are normally fixed size.

  ## Waiting for computations

  Q:
  Could you please tell me what's the best way to tackle the following problem? I would like to have a modal dialog that shows the user some useful information about a time-consuming operation. Basically, I want to open a modal dialog, start the computation and let the computation update the dialog's command objects. How can this be done? If the dialog is not modal it would be no problem, but I definitely want to block all input to the application. What I need is some routine to Show a modal dialog but returning immediately so that the program can proceed.

  A:

  This is a hard problem for V, unfortunately. X and Windows handle modal dialogs somewhat differently, so there is not a portable solution that V could support.

  But one suggestion is to add a "Begin Computation" button to the modal dialog. Then in the dialog's DialogCommand method, call the code to do the computation. That code should call vApp::CheckEvents periodically to keep the system working, but I think this will give you the effect you want, more or less. While the call to the computation would not return until it was done, the calls to vApp::CheckEvents would allow a Cancel button to work within the modal dialog, which would then need to call a routine in your code to set a cancel flag, or something like that. You could also set flags within the modal dialog that it is in the middle of a computation and behave accordingly.

  I haven't tried this, but I'm pretty sure this technique can work. It does require a "Begin" button, however, which might not work the way you want.

  I also think that you could keep a state flag of your own, and override all DialogCommand and WindowCommand methods to ignore any messages while in compute mode. I think the message from the V close box on X, or the system close box on Windows might go around these, but then that might still be how you want it to work - exit if the user says so.