MATLAB Programming

10 Scheduling Program Execution with Timers
Note When you specify the callback commands directly as the value of the
callback function property, the commands are evaluated in the MATLAB
workspace.
Putting Commands in a Callback Function
Instead of specifying MATLAB commands directly as the value of a callback
property, you can put the commands in an M-file and specify the M-file as the
value of the callback property.
When you create a callback function, the first two arguments must be a
handle to the timer object and an event structure. An event structure contains
two fields: Type and Data. TheType field contains a text string that identifies
the type of event that caused the callback. The value of this field can be any of
the following strings: 'StartFcn', 'StopFcn', 'TimerFcn', or'ErrorFcn'.
The Data field contains the time the event occurred.
In addition to these two required input arguments, your callback function can
accept application-specific arguments. To receive these input arguments, you
must use a cell array when specifying the name of the function as the value
of a callback property. For more information, see “Specifying the Value of
Callback Function Properties” on page 10-17.
Example: Writing a Callback Function
This example implements a simple callback function that displays the type
of event that triggered the callback and the time the callback occurred. To
illustrate passing application-specific arguments, the example callback
function accepts as an additional argument a text string and includes this text
string in the display output. To see this function used with a callback property,
see“SpecifyingtheValueofCallbackFunction Properties” on page 10-17.
function my_callback_fcn(obj, event, string_arg)
txt1 = ' event occurred at ';
txt2 = string_arg;
event_type = event.Type;
event_time = datestr(event.Data.time);
10-16