Having a problem using String Lists

harrzack

(Repost with hopefully correct code paste and the somewhat arcane method of indicating code...)

I'm attempting to use String Lists to create a simple scrolling text display. Below is a test snippet to show the prob I'm having with String Lists. The For Loop moves each line up, starting from the top and moving down. It appears there is a bug or problem with the String List 'get' function. If you break inside the for loop that does the scroll, you see in the variables that 'line' keeps getting a NULL value - and I suspect this is why the scroll doesn't really work.

Are there any known problems with the String lists, or am I just not using it correctly?

Code follows:

String curmsg[];  // Holds current message loaded from data folder
StringList vp;      // Will hold each line to be displayed on the view port
String line;

int i, j, k, vpWdoSize = 21;



void setup() {
  size(500, 440); // Width, Height; X-coord, Y-coord
  vp = new StringList();
  setvp();
  frameRate(5);

}

void draw() {
  background(0);
  for ( i=vpWdoSize-1; i<=0; i--) {
    vp.set(i, vp.get(i-1));  // EG: Line 19 moves to line 20; then line 18 moves to 19, etc...
    text(vp.get(i),30,50);
  }
  vp.set(0,k++ +" new data");
  text(frameCount+" dummy",30,random(30,420));

}

void setvp(){
  for (i=0; i<vpWdoSize; i++) {
    vp.set(i,"mt-"+i );  // initialize the viewport array

  }
  k = 0;

harrzack

Sorry - I read that you are supposed to 'Copy as HTML' to post in the code - it did look good in the preview - now in the live listing it gets broke.... Why is is so @#_@#@ difficult to post code in a programming forum?????

GoToLoop

This forum uses Markdown rather than HTML:
https://forum.Processing.org/two/discussion/8045/how-to-format-code-and-text
https://en.Wikipedia.org/wiki/Markdown

harrzack

Ok - but struggling enough with Processing - no time to learn Markdown! :-(

I've tried it and still had bad results. Can I delete this post and try over?

GoToLoop

We can always edit our own posts! Just re-paste your code according to the "Format Code' article.

harrzack

Will give it a go. I did use the 'C' button previously, got the two tic marks, pasted my code between, and when I did a preview - it did NOT show any formatting - which is why I tried something else. Will try an edit now...

GoToLoop

Pasted first, highlight it and then CTRL+O.
If we hit CTRL+O 1st, we'll only get a pair of apostrophes.
That's only for 1 inline code statement.

harrzack

Yeah - finally got it - the paste/hightlight/C button sorta threw me... not intuitive but once you know it - pretty easy. Like trying to drive around in Phila, PA!

GoToLoop

I particularly don't rely on CTRL+O nor button C.
Instead still in the PDE: CTRL+T, CTRL+A, TAB, TAB, CTRL+C.
Only then CTRL + V here in the forum. :-bd

benja

I don't think there is anything wrong with Lists. You make a mistake in your for-loop. You start with i beeing 20 and the stop-condition is i<=0. That is true right from the start, so the code inside of the loop will never be executed.

But since we have a list, we can add and remove items from that list, which makes it easy to "scroll" the items. Here is an example:

void draw() {
  background(0);

  // copy first entry
  String tmp = vp.get(0);
  // remove first entry
  vp.remove(0);
  // add copy of first entry to the end of the list
  vp.push(tmp);

  // display all of the entries
  for ( int i=0; i<vp.size(); i++) {
    text(vp.get(i), 30, i*20);
  }
}

harrzack

benja - thanks for catching that error! Also wasn't aware of the .push feature. Figured I had to be doing something dumb.

GoToLoop

Also wasn't aware of the .push feature.

Neither moi! They still hadn't published those new methods in the reference either:
https://Processing.org/reference/StringList.html

But it's merely an alias for append():
https://Processing.org/reference/StringList_append_.html
https://GitHub.com/processing/processing/blob/master/core/src/processing/data/StringList.java#L164

/** Just an alias for append(), but matches pop() */
public void push(String value) {
  append(value);
}

There's also appendUnique(), but not pushUnique()! :P
https://GitHub.com/processing/processing/blob/master/core/src/processing/data/StringList.java#L318