How can I pass a variable (numeric) through a callback event when I pressed a key in my figure?

5 次查看（过去 30 天）
Guilherme Lima
Guilherme Lima 2021-10-20
回答： Walter Roberson 2025-4-30
Hello,
I have an issue;
I am collecting data in a while loop and I want to store this data in my callback event when I press a key in my figure.
This does not work at all.
Could you please help me in this topic?
My code example:
set(gcf, 'KeyPressFcn', {@GetData, calibration});
while true
pause(0.00001);
[calibration] = ml_CANapeReadCalibrationObject(moduleHandle(1,2), 'F_DE_f_1', 1);
sensorData = [sensorData; calibration(1)];
plot(sensorData);
drawnow;
disp('getting data');
end
function GetData(src, event, sensorData)
finalData = [finalData; sensorData];
pause(1);
end
  2 个评论
Jan
Jan 2021-10-20
This piece of code is not running. It is not clear if the callback is a nested function or not. "Does not run at all" is not useful to explain the problem. Do you get an error message?
Guilherme Lima
Guilherme Lima 2021-10-21
编辑：Guilherme Lima 2021-10-21
There is the following error message
Undefined function or variable 'finalData'.
Error in FinalVersion_lateral_FoV>GetData (line 155)
finalData = [finalData; sensorData];
Error while evaluating Figure KeyPressFcn.
What is happening is that my variable sensorData is empty inside the function.
In the loop while, the variable sensroData is receving the value properly, but when I press some button in the keyboard, the function GetData is not getting the value that is in the variable sensorData.
I hope that is clear now. Please, let know if it is not.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（2 个）

Walter Roberson
Walter Roberson 2025-4-30
set(gcf, 'KeyPressFcn', {@GetData, calibration});
That code does not bind "calibration" to whatever the then-current value of the variable "calibration" is. Instead, it reads the value of the variable "calibration" as of the time that the set() is performed, and sets the KeyPressFcn to use that recorded version of "calibration".
There is no syntax for setting the KeyPressFcn for retrieving the then-current value of a variable. You would have do something such as continually assigning the variable in the 'base' workspace, and telling the KeyPressFcn to evalin('base')
finalData = [finalData; sensorData];
finalData is not defined inside of that function. You would have to something such as making it a shared variable and making GetData a nested function.
Vedant Shah
Vedant Shah 2025-4-30
Hi @Guilherme Lima,
To store the data present in “sensorData”, it is essential to ensure that the callback function receives the correct value of the “sensorData” variable. The following approach can be utilized which makes use of “setappdata” and “getappdata”:
Firstly, modify the setting line to ensure that no data is passed in the callback function:
set(gcf, 'KeyPressFcn', @GetData);
The “setappdata” function can be used to store the variable “sensorData” . It can be added just before plotting it:
setappdata(gcf, 'sensorData', sensorData);
Additionally, the “GetData” function can be modified to make use of “getappdata” and to ensure that the “finalData” variable remain conistent:
function GetData(src, event)
sensorData = getappdata(src, 'sensorData');
persistent finalData
if isempty(finalData)
finalData = [];
end
finalData = [finalData; sensorData];
pause(1);
end
The use of the “persistent” keyword ensures consistency when saving values multiple times during code execution.
For further information, refer to the following MATLAB documentation links:

类别

在 Help Center 和 File Exchange 中查找有关 Structures 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by