Testing for Hold State :: Handle Graphics Objects (Graphics)

Graphics

Testing for Hold State

There are situations in which your M-file should change the visual appearance of the axes to accommodate new graphics objects. For example, if you want the M-file my_plot from the previous example to accept 3-D data, it makes sense to set the view to 3-D when the input data has z-coordinates.

However, to be consistent with the behavior of the MATLAB high-level routines, it is good practice to test whether hold is on before changing parent axes or figure properties. When hold is on, the axes and figure NextPlot properties are both set to add.

The M-file my_plot3 accepts 3-D data and also checks the hold state, using ishold, to determine whether it should change the view.

function my_plot3(x,y,z)
cax = newplot;
hold_state = ishold; % ishold tests the current hold state
LSO = ['- ';'--';': ';'-.'];
if nargin == 2
    hlines = line(x,y,'Color','k');
    if ~hold_state % Change view only if hold is off
        view(2)
    end
elseif nargin == 3
    hlines = line(x,y,z,'Color','k');
    if ~hold_state % Change view only if hold is off
        view(3)
    end
end
ls = 1;
for hindex = 1:length(hlines)
    if ls > length(LSO),ls = 1;end
    set(hlines(hindex),'LineStyle',LSO(ls,:))
    ls = ls + 1;
end

If hold is on when you call my_plot3, it does not change the view. If hold is off, my_plot3 sets the view to 2-D or 3-D, depending on whether there are two or three input arguments.

Example -- Using newplot Protecting Figures and Axes