Periodically Updated Static Text and Reading from Key-Value File

I have two questions concerning a GUI application I'm writing:

1. Is it possible to code a static text label so it periodically updates itself (from a database, or whatever) without interfering with the execution of the main application? The label would be used to cycle through news, updates, etc. That sort of thing.
2. Currently, my application sets user-supplied variables by running a script, generate_appvars. I'll be compiling soon, but want to preserve this method of reading in run params at runtime. I was thinking a key-value params file which I can read into a dynamically named struct, but am unsure of how to handle vector and cell assignments (k/v pairs key = [1, 3, 5] or key = {'this', 'that'} for instance). Thinking of using eval for the right hand assignment, but don't think it's the best solution. How do other people handle runtime parameters like this?

Thanks!

Answer 1

[Fangjun Jiang]

For 1, you can probably use a timer object and set up the callback to refresh your text label.

For 2, you can use the parameter file to specify your key-value pairs:

par1, 1
par2, 2
par3, 3

After reading in the files, try to organize the data as:

Keys={'par1','par2','par3'}; Values={1,2,3};

Then run

a=cell2struct(Values,Keys,2)

You will get a.par1, a.par2, a.par3 holding the correct value and you've avoided the notorious evil eval.

Answer 2

[Meric Ozturk]

Thanks guys, the timer suggestion worked perfectly. If anyone runs into problem #2, my implementation's below (based around Fangjun's suggestion). I'll add a function version to FEX when I get a chance. The code reads key-value assignments in matlab syntax into struct p, ignoring lines beginning with '#'.

%%Populate parameters struct from parameters.txt
fid = fopen('parameters.txt', 'r');
if fid < 0; error('Parameters file is missing. Please replace.'); end
% Extract key-value pairs from params file
keys = {}; values = {};
while ~feof(fid)
    this_line = fgets(fid);
    % Check to see if the line is a comment or whitespace
    switch this_line(1)
        case {'#', ' ', char(10)}
        otherwise
            % First token is key; second is value
            [keys{end+1} inds] = strtok(this_line, '=');
            values{end+1} = strtok(inds, '=');
            % If the value is convertible to num, convert to num
            if ~isnan(str2double(values{end}))
                values{end} = str2double(values{end});
            end
    end
end
fclose(fid);
% Remove extra padding from key-value pairs
keys = strtrim(keys); 
str_ind = cellfun(@ischar, values);
values(str_ind) = strtrim(values(str_ind));
% Remove extra ' ' around strings
data_type_ind = [];
for i = find(str_ind)
    str = values{i};
    if str(1) == ''''
        values{i} = str(2:end-1);
    else
        data_type_ind(end+1) = i;
    end
end
% Convert data type assignments to actual data types
% This may actually be a valid use of the eval function!
for i = data_type_ind
    eval(['values{i} = ' values{i} ';']);
end
% Construct parameter struct from read key-value pairs
p = cell2struct(values, keys, 2);

[Fangjun Jiang]

Good work!+1

Answer 3

[Walter Roberson]

1. No -- background activity always interferes with the execution of the main application.

Perhaps for your purposes it would be acceptable to code a timer whose callback fetched the data and set() the text control to the new content.

2. regexp() can help with the parsing -- though matching apostrophes can be a pain if your strings are allowed to include apostrophes.