### 35.4 GUI Utility Functions

These functions do not implement a GUI element but are useful when developing programs that do. The functions `uiwait`, `uiresume`, and `waitfor` are only available with the `qt` or `fltk` toolkits.

Function File: used = desktop ("-inuse")

  Return true if the desktop (GUI) is currently in use.

  See also: isguirunning.

Function File: data = guidata (h)
Function File: guidata (h, data)

  Query or set user-custom GUI data.

  The GUI data is stored in the figure handle h. If h is not a figure handle then it’s parent figure will be used for storage.

  data must be a single object which means it is usually preferable for it to be a data container such as a cell array or struct so that additional data items can be added easily.

  See also: getappdata, setappdata, get, set, getpref, setpref.

Function File: hdata = guihandles (h)
Function File: hdata = guihandles

  Return a structure of object handles for the figure associated with handle h.

  If no handle is specified the current figure returned by `gcf` is used.

  The fieldname for each entry of hdata is taken from the `"tag"` property of the graphic object. If the tag is empty then the handle is not returned. If there are multiple graphic objects with the same tag then the entry in hdata will be a vector of handles. `guihandles` includes all possible handles, including those for which `"HandleVisibility"` is `"off"`.

  See also: guidata, findobj, findall, allchild.

Built-in Function: have_window_system ()

  Return true if a window system is available (X11, Windows, or Apple OS X) and false otherwise.

  See also: isguirunning.

Built-in Function: isguirunning ()

  Return true if Octave is running in GUI mode and false otherwise.

  See also: have_window_system.

Function File: uiwait
Function File: uiwait (h)
Function File: uiwait (h, timeout)

  Suspend program execution until the figure with handle h is deleted or `uiresume` is called.

  When no figure handle is specified this function uses the current figure. If the figure handle is invalid or there is no current figure, this functions returns immediately.

  When specified, timeout defines the number of seconds to wait for the figure deletion or the `uiresume` call. The timeout value must be at least 1. If a smaller value is specified, a warning is issued and a timeout value of 1 is used instead. If a non-integer value is specified, it is truncated towards 0. If timeout is not specified, the program execution is suspended indefinitely.

  See also: uiresume, waitfor.

Function File: uiresume (h)

  Resume program execution suspended with `uiwait`.

  The handle h must be the same as the on specified in `uiwait`. If the handle is invalid or there is no `uiwait` call pending for the figure with handle h, this function does nothing.

  See also: uiwait.

Built-in Function: waitfor (h)
Built-in Function: waitfor (h, prop)
Built-in Function: waitfor (h, prop, value)
Built-in Function: waitfor (…, "timeout", timeout)

  Suspend the execution of the current program until a condition is satisfied on the graphics handle h.

  While the program is suspended graphics events are still being processed normally, allowing callbacks to modify the state of graphics objects. This function is reentrant and can be called from a callback, while another `waitfor` call is pending at the top-level.

  In the first form, program execution is suspended until the graphics object h is destroyed. If the graphics handle is invalid, the function returns immediately.

  In the second form, execution is suspended until the graphics object is destroyed or the property named prop is modified. If the graphics handle is invalid or the property does not exist, the function returns immediately.

  In the third form, execution is suspended until the graphics object is destroyed or the property named prop is set to value. The function `isequal` is used to compare property values. If the graphics handle is invalid, the property does not exist or the property is already set to value, the function returns immediately.

  An optional timeout can be specified using the property `timeout`. This timeout value is the number of seconds to wait for the condition to be true. timeout must be at least 1. If a smaller value is specified, a warning is issued and a value of 1 is used instead. If the timeout value is not an integer, it is truncated towards 0.

  To define a condition on a property named `timeout`, use the string `\timeout` instead.

  In all cases, typing CTRL-C stops program execution immediately.

  See also: waitforbuttonpress, isequal.