Wonderful timing, Yair. I’m building a complex gui with a lot of my debugging just printing to the screen. My next task/idea was to implement such a log panel. I want to make debugging easier, so I was thinking of making each of my logged messages also have a “debugLevel”. While testing, my application can have a low “debugThreshold”, so that all messages get shown. For production, I can set a higher debugThreshold so that only user-relevant message get shown.

In your experience, have you preferred something like this (ALL messages are generated by the application and sent to the logger, but they’re only printed if they have a high enough debugLevel), or something where you wrap each of your debug strings with:

 
if debugThreshold>3
    logMessage('hey ho')
end

The first method has the highest cost (all messages are created), while the second method is just a little more cumbersome (needing to wrap messages in if-statements inline with your application code).

By the way, there’s a little hiccup in the html parsing of “nargin<3" printing the full code of "nargin<3"

@Sven – thanks, the HTML hickup is fixed.

I normally prefer setting some global config indicating the minimal display level. Within the logging function, I then compare the severity of the reported message to the config value and bail out of the function if the message should not be logged. I normally use either 3 severity levels (INFO, WARN, ERROR) or 5 (DEBUG, INFO, WARN, ERROR, FATAL), with the default config level being either INFO or WARN. Naturally this can and should be wrapped in some nice logging class, but I never took the time to do this until now…

Thanks Yair, makes sense to me.

I’ve also mused about how, in the production version of any code, it would be great to just snip out all debug-level commands. I’ve considered putting in my own comment-based markup such as:

 
a = magic(3);
% $DEBUG-BEGIN$
if DEBUG_LEVEL > 0
  aStr = sprintf('%g,',a);
  fprintf('Contents of ''a'' are: %s\n',aStr)
end
% $DEBUG-END$
... % rest of code

With syntax like that, you could have the best both worlds. During testing you can run the original code and set the DEBUG_LEVEL to whatever prints your chosen output. Then for production you can have a script that automatically comments out code between $DEBUG-BEGIN$ and $DEBUG-END$ tags, which means that in the production version, you don’t even get the (minor) overhead of checking debug levels throughout the code.

But yes… sometimes it’s easier to think of a good idea than find the time to implement it 🙂

Hi Yair,

Another great post. I was just wondering if you could explain the following lines, which seem to do nothing.

currentHTML = char(jEditbox.getText);
jEditbox.setText(strrep(currentHTML,'',newText));

Is this a typo/bug, or am I missing something?

@Chris – it’s good that you noticed. This is in fact due to problematic rendering of the code by my blog server engine. The original code in the second line was jEditbox.setText(strrep(currentHTML,'</body>',newText)); and the purpose is to replace the HTML body-end tag with the new text.

Since I couldn’t get around my blog engine’s limitation, I have now replaced that line with the equivalent (although a little more obscure):

jEditbox.setText(strrep(currentHTML,[60 '/body>'],newText));

I’ve implemented this log, but I had a few questions about it. ^[22], and I was hoping you would weigh-in.

After getting some feedback on stackexchange, I have a way to dramatically improve performance. Instead of performing getText and setText, you can insert the new HTML at the end of the document in the following way

function logMessage(jEditbox, text)
text = [text ''];

% Place the HTML message segment at the bottom of the editbox
Doc = jEditbox.getDocument();
jEditbox.getEditorKit().read(java.io.StringReader(text), Doc, Doc.getLength());
jEditbox.setCaretPosition(Doc.getLength());
end

[…] to Yair Altman’s excellent post on undocumentedmatlab.com, I’ve tried to implement a GUI logging program using a rich editbox […]

Hi Yair,

I was using this for some time (from older posts).
But in R2013b (all prior versions work), the hyperlink feature broke. Not completely, but the mouse cursor doesn’t change to a hand when hovering over a hyperlink.

In addition the following code also does nothing:

jHelpLinkButton = java(findjobj(hButton));
jHelpLinkButton.setCursor(java.awt.Cursor.getPredefinedCursor(java.awt.Cursor.HAND_CURSOR));

When using a “com.mathworks.widgets.HyperlinkTextLabel” (from your book), also the hand cursor doesn’t appear, but at least, the label changes color when hovering.

Any idea, how I can get this working again?
An acceptable workaround would be to change the hyperlink style, so it has an alternate color when hovering over it. But I think I would have to change the default style for hyperlinks in the HTMLEditorKit…

@Holger – this is probably related to the fact thar R2013b started using Java 7, which is a major overhaul over the previous Java 6. I assume that this broke some functionality of the editbox. Since the underlying Java control is a standard ^[23], you can easily search the net for relevant reports of (and possible workarounds for) this issue. Let us know if you find something relevant.

Hello Yair,

is there a way to get rid of the vertical scrollbar? I tried to do so using

jScrollPane.setVerticalScrollBarPolicy(javax.swing.JScrollPane.VERTICAL_SCROLLBAR_NEVER)

but this has no effect.

Thanks,
Carsten

@Carsten – it should work, you’re probably doing something wrong. Perhaps you are updating the wrong handle, or updating the editbox’s contents via Matlab not Java (this resets the Java customizations).

[…] is to use small icon images checked and unchecked as part of the listbox item labels. As I explained last year, listboxes (like all other Matlab uicontrols that rely on underlying Java Swing […]

This is a cool stuff! I need to use rather text than html and am having a problem with getting the code to work. Since I need to put so many lines in the log, I thought something to append a new line would be computationally less demanding than setText (is that true?). I mean something like,

jEditbox.append(new_text);

Would this be possible?
Another question: Since I don’t know Java, I have no clue about what kind of member functions are available. How can one know that?

@Daisuke – there is no append method (by this or any other name) that I know of.

To list a Java object’s methods, you can use the builtin methods or methodsview functions, or one of my utilities: ^[24] or ^[25].