Cheat sheets

The most frequent decisions, condensed. All snippets compile against the 2026 API.

Layouts — add() signature

// VerticalLayout / HorizontalLayout — first the size, then the component
add(LAY_FILL, comp);   // -1f → fills the remaining space (the "elastic")
add(LAY_AUTO, comp);   //  0f → content's natural size
add(0.2f, comp);       // >0  → 20% of the container's total dimension

// GridLayout — ALL the widths, then ALL the components
add(0.35f, 0.65f, new Label("Nome"), new TextField(""));

// EvenlySpacedLayout — only the component (spaces evenly; does not size)
add(icone1); add(icone2);

// RelativeLayout — anchors (see matrix below)
add(comp, RelPos.AFTER, RelPos.CENTER_OF, RelSize.AUTOSIZE, RelSize.AUTOSIZE, refComp);

Detail per layout: ui/layouts/.

RelativeLayout — matrix

add(alvo, RelPos x, RelPos y, RelSize larg, RelSize alt [, Component ref] [, Gap outgap]);

Relative — responsive dimensions

Relative.ofFont(1.5f);                     // 1.5 × font height (scales with the UI)
Relative.ofScreen(0.8f);                   // 80% of the screen
Relative.ofScreen(0.5f, ScreenSize.MIN);   // 50% of the SMALLER side (adapts portrait/landscape)
Relative.ofPixels(24f);                    // fixed pixel (use as an exception)

Colors — ARGB 0xAARRGGBB

int opaco     = 0xFF2196F3;                       // alpha FF = fully visible
int invisivel = 0x002196F3;                       // ⚠️ alpha 00 → does NOT appear
int meio      = ColorUtils.withAlpha(0xFF2196F3, 128);  // 50% transparent
int escuro    = ColorUtils.darker(0xFF2196F3, 0.2f);
int claro     = ColorUtils.lighter(0xFF2196F3, 0.2f);
int mistura   = ColorUtils.lerpColor(corA, corB, 0.5f);

Alpha trap: an int without the alpha byte (0xRRGGBB) has alpha 0 → the component becomes invisible. Always include 0xFF... for opaque.

Threading — return/run

Component.onUI(() -> { ... });               // returns to the paint thread (from any thread)
Main.runOnPaintThread(() -> { ... });         // same, outside of a Component
Main.runOnPaintThreadAndWait(() -> { ... });  // same, blocking until it finishes
comp.onActionThread(c -> { ... });            // reacts to an event on a background thread
Component.repaint();                          // requests a new frame (render on demand)

Why: The paint thread.

See also

• Enums and UIConstants · Layouts · Colors (Ch. 11)