Handles in Logical Expressions
Handle objects do not evaluate to logical
You must use the function that tests for the state of interest and
returns a logical value.
If Handle Is Valid
isgraphics to determine if a variable
contains a valid graphics object handle. For example, suppose
a variable in the workspace. Before operating on this variable, test
if isgraphics(hobj) ... end
You can also determine the type of object:
if isgraphics(hobj,'figure') ...% hobj is a figure handle end
If Result Is Empty
You cannot use empty objects directly in logical statements.
isempty to return a logical
value that you can use in logical statements.
Some properties contain the handle to other objects. In cases where the other object does not exist, the property contains an empty object:
close all hRoot = groot; hRoot.CurrentFigure
ans = 0x0 empty GraphicsPlaceholder array.
For example, to determine if there is a current figure by querying
CurrentFigure property, use the
hRoot = groot; if ~isempty(hRoot.CurrentFigure) ... % There is a current figure end
Another case where code can encounter an empty object is when
searching for handles. For example, suppose you set a figure’s
to the character vector
'myFigure' and you use
findobj to get the handle of this figure:
if isempty(findobj('Tag','myFigure')) ... % That figure was NOT found end
findobj returns an empty object if there
is no match.
If Handles Are Equal
There are two states of being equal for handles:
Any two handles refer to the same object (test with
The objects referred to by any two handles are the same class, and all properties have the same values (test with
Suppose you want to determine if
h is a handle
to a particular figure that has a value of
if h == findobj('Tag','myFigure') ...% h is correct figure end
If you want to determine if different objects are in the same
hLine1 = line; hLine2 = line; isequal(hLine1,hLine2)
ans = 1