Close uialert figure by button click

Question

Based on a MATLAB example, I added a close command in order to close the uifigure after pressing the OK button. However, in its current state the figure is closed automatically, rather than on the button click. How can I alter the below to have the figure close on click?

Code:

fig = uifigure;
message = {'Fire hazard!','Consider reducing temperature.'};
uialert(fig,message,'Warning',...
'Icon','warning');
close(fig)

Answer 1

You should use a callback in uialert:

fig = uifigure;
message = {'Fire hazard!','Consider reducing temperature.'};
uialert(fig, message, 'Warning', 'Icon', 'warning', ...
        'CloseFcn', @(~, ~)close(fig));  % This will be executed after Ok is pressed

The syntax @ is the Matlab way to define an anonymous function (Matlab calls these function handles, other languages usually call these lambdas). It allows passing functions as parameters to other functions. If your anonymous function needs to receive parameters, the syntax @(p1, p2, p3) can be used.

In the case of callbacks for uifigures, the callbacks always expect two parameters: fig and event. fig is the figure where the event happened, event is a structure describing the event. In the case above, since all you want to do is close the figure (and you already know which figure you want to close), you can ignore both parameters. The syntax in Matlab to tell that you are receiving a parameter that you purposefully are ignoring is by using a tilde (~) in the position of the parameter. This can be used anywhere actually, including in the definition of normal functions or when unpacking the return value. For example:

[U,~,V] = svd(A)

tells that you are not interested in the singular values of your SVD, only in left and right singular vectors.

You can read more about function handles in the Matlab documentation.