How to let ControlP5 Dropodownlist open up instead of down?

Question

Using this MWE from the documentation:

import controlP5.*;
import java.util.*;


ControlP5 cp5;

void setup() {
  size(400, 400);
  cp5 = new ControlP5(this);
  List l = Arrays.asList("a", "b", "c", "d", "e", "f", "g", "h");
  /* add a ScrollableList, by default it behaves like a DropdownList */
  cp5.addScrollableList("dropdown")
     .setPosition(100, 100)
     .setSize(200, 100)
     .setBarHeight(20)
     .setItemHeight(20)
     .addItems(l)
     // .setType(ScrollableList.LIST) // currently supported DROPDOWN and LIST
     ;
     
     
}

void draw() {
  background(240);
}

How can I get the dropdownlist to open up instead of down? I'm trying to place the list towards the lower edge of my screen. I could not find an option in the documentation.

Answer 1

Because of ControlP5's use of Java Generics inheritance is actually quite tricky in this case should ScrollableListView's display() method be overriden:

• ScrollableList extends Controller< ScrollableList >
• in java a class can subclass a single class, not multiple, hence the customized subclass like PopUpScrollableList would inherit Controller< ScrollableList > , not Controller< PopUpScrollableList >
• there are a bunch of properties accessed in ScrollableListView's display() which belong to ScrollableList which are either private or protected

TLDR; @laancelot's suggestion to clone the library, modify the ScrollableListView's display() method directly and recompiling the library sounds like the easier option compared subclassing to a custom scroll list.

That being said, setting up an IDE and compiling a java library might not be the friendliest thing for a beginner, hence I can recommend a hacky workaround: simply shift the list's y position so it appears to be above instead of bellow:

import controlP5.*;
import java.util.*;


ControlP5 cp5;

ScrollableList list;
int listX = 100;
int listY = 100;
int listWidth = 200;
int listHeight = 100;
int barHeight = 20;

void setup() {
  size(400, 400);
  cp5 = new ControlP5(this);
  List l = Arrays.asList("a", "b", "c", "d", "e", "f", "g", "h");
  /* add a ScrollableList, by default it behaves like a DropdownList */
  list = cp5.addScrollableList("dropdown")
     .setPosition(listX, listY)
     .setSize(listWidth, listHeight)
     .setBarHeight(barHeight)
     .setItemHeight(20)
     .addItems(l)
     // .setType(ScrollableList.LIST) // currently supported DROPDOWN and LIST
    ;
 
     
     
}

void draw() {
  // hack: shift the list up when it's open
  if(list.isOpen()){
    list.setPosition(listX, listY - listHeight + barHeight);
  }else{
    list.setPosition(listX, listY);
  }
  background(240);
}

It's not perfect visually, may be a potentially akward user experience, but it's the simplest option for this custom behaviour using ControlP5.

Alternatively it's worth looking at customising a different UI library or writin a custom list.

For the sake of argument, here's an modified version of the list example from theGuido library:

/**
 *    A list
 *
 *
 *    Make sure to try your scroll wheel!
 */

import de.bezier.guido.*;

Listbox listbox;
SimpleButton button;
Object lastItemClicked;

void setup ()
{
    size(400, 400);
    
    // make the manager
    
    Interactive.make( this );
    
    // create a list box
    listbox = new Listbox( 20, 30, width-40, height-80 );
    for ( int i = 0, r = int(10+random(100)); i < r; i++ )
    {
        listbox.addItem( "Item " + i );
    }
    listbox.visible = false;
    // create button
    button = new SimpleButton("pop-up list", 20, 350, width-40, 24 );
    
}

void draw ()
{
    background( 20 );
    listbox.visible = button.on;
    if ( lastItemClicked != null )
    {
        fill( 255 );
        text( "Clicked " + lastItemClicked.toString(), 30, 20 );
    }
}

public void itemClicked ( int i, Object item )
{
    lastItemClicked = item;
}

public class Listbox
{
    float x, y, width, height;
    
    ArrayList items;
    int itemHeight = 20;
    int listStartAt = 0;
    int hoverItem = -1;
    
    float valueY = 0;
    boolean hasSlider = false;
    boolean visible = true;
    
    Listbox ( float xx, float yy, float ww, float hh ) 
    {
        x = xx; y = yy;
        valueY = y;
        
        width = ww; height = hh;
        
        // register it
        Interactive.add( this );
    }
    
    public void addItem ( String item )
    {
        if ( items == null ) items = new ArrayList();
        items.add( item );
        
        hasSlider = items.size() * itemHeight > height;
    }
    
    public void mouseMoved ( float mx, float my )
    {
        if(!visible){
          return;
        }
        if ( hasSlider && mx > width-20 ) return;
        
        hoverItem = listStartAt + int((my-y) / itemHeight);
    }
    
    public void mouseExited ( float mx, float my )
    {
        if(!visible){
          return;
        }
        hoverItem = -1;
    }
    
    // called from manager
    void mouseDragged ( float mx, float my )
    {
        if(!visible){
          return;
        }
        if ( !hasSlider ) return;
        if ( mx < x+width-20 ) return;
        
        valueY = my-10;
        valueY = constrain( valueY, y, y+height-20 );
        
        update();
    }
    
    // called from manager
    void mouseScrolled ( float step )
    {
        if(!visible){
          return;
        }
        valueY += step;
        valueY = constrain( valueY, y, y+height-20 );
        
        update();
    }
    
    void update ()
    {
        if(!visible){
          return;
        }
        float totalHeight = items.size() * itemHeight;
        float itemsInView = height / itemHeight;
        float listOffset = map( valueY, y, y+height-20, 0, totalHeight-height );
        
        listStartAt = int( listOffset / itemHeight );
    }
    
    public void mousePressed ( float mx, float my )
    {
        if(!visible){
          return;
        }
        if ( hasSlider && mx > width-20 ) return;
        
        int item = listStartAt + int( (my-y) / itemHeight);
        itemClicked( item, items.get(item) );
    }

    void draw ()
    {
        if(!visible){
          return;
        }
        noStroke();
        fill( 100 );
        rect( x,y,this.width,this.height );
        if ( items != null )
        {
            for ( int i = 0; i < int(height/itemHeight) && i < items.size(); i++ )
            {
                stroke( 80 );
                fill( (i+listStartAt) == hoverItem ? 200 : 120 );
                rect( x, y + (i*itemHeight), this.width, itemHeight );
                
                noStroke();
                fill( 0 );
                text( items.get(i+listStartAt).toString(), x+5, y+(i+1)*itemHeight-5 );
            }
        }
        
        if ( hasSlider )
        {
            stroke( 80 );
            fill( 100 );
            rect( x+width-20, y, 20, height );
            fill( 120 );
            rect( x+width-20, valueY, 20, 20 );
        }
    }
}

public class SimpleButton
{
    float x, y, width, height;
    boolean on;
    
    String label = "";
    
    SimpleButton ( float xx, float yy, float w, float h )
    {
        x = xx; y = yy; width = w; height = h;
        
        Interactive.add( this ); // register it with the manager
    }
    
    SimpleButton ( String label, float xx, float yy, float w, float h )
    {
      this(xx, yy, w, h);
      this.label = label;
    }
    
    // called by manager
    
    void mousePressed () 
    {
        on = !on;
    }

    void draw () 
    {
        if ( on ) fill( 200 );
        else fill( 100 );
        
        rect(x, y, width, height);
        
        if ( on ) fill( 100 );
        else fill( 200 );
        
        text(label, x + 10, y + this.height * 0.65);
    }
}

The code is a lot more verbose in the sketch, but could be moved to a separate GUI tab. Hopefully because it is simpler it can be manipulated easier than ControlP5 for custom behaviours.