Motion is a statement about what just happened, so the kind follows the event. Something * arrived or left — fade. Something moved from here to there — position. Something is ongoing with * no known end — loop. Motion that answers none of those is decoration, and decoration is the first * thing a user reads as the app being slow.
* *None of the three owns a component. Each produces a number over time and hands it to * you; what the number means is the screen's business. That is why the same {@link LoopAnimation} * drives a colour here and could drive a radius, a rotation or an alpha elsewhere.
*/ public class R22Animation extends Recipe { private Label fading, moving, pulsing; private LoopAnimation loop; public String title() { return "Animation"; } public String note() { return "Styles.animationDuration is the house value — match it, so the app moves at one" + " speed. Anything the user waits through twice was too long the first time."; } public void build(Component body) throws Exception { head(body, 0xE65F, "Arriving and leaving", Tones.accent()); fading = label("I fade out and back", 1.5f, true, Styles.primaryColor, Position.START); body.add(LAY_AUTO, outgap(fading, 0, 0, 0, .4f)); button(body, "Fade it", this::fade); head(body, 0xE8D5, "Moving from here to there", Tones.support()); moving = label("I slide", 1.5f, true, Styles.textColor, Position.START); moving.testTag("anim.slide"); body.add(LAY_AUTO, outgap(moving, 0, 0, 0, .4f)); button(body, "Slide it", this::slide); head(body, 0xE627, "Ongoing, with no end", Tones.highlight()); pulsing = label("I pulse while something is happening", 1f, false, Styles.captionColor, Position.START); body.add(LAY_AUTO, outgap(pulsing, 0, 0, 0, .4f)); button(body, "Start / stop", this::togglePulse); } private void fade() { final AlphaAnimation a = new AlphaAnimation(1f, .1f, Styles.animationDuration); a.onUpdate(() -> { // getValue() is the number the animation is at right now. Turning it into an alpha is // this screen's decision, not the animation's. fading.getStyle() .textColor(ColorUtils.withAlpha(Styles.primaryColor.color(), a.getValue())); Screen.repaint(); }); // Reversing on complete, so the label ends where it started and the demo can be run twice. a.onComplete(() -> { final AlphaAnimation back = new AlphaAnimation(.1f, 1f, Styles.animationDuration); back.onUpdate(() -> { fading.getStyle() .textColor(ColorUtils.withAlpha(Styles.primaryColor.color(), back.getValue())); Screen.repaint(); }); back.start(); }); a.start(); } private void slide() { final PositionAnimation p = new PositionAnimation(0f, 8f, .45f); p.onUpdate(() -> { // An outgap in font units — so the distance is the same on every density, which a // distance in pixels is not. moving.getStyle() .outgap(Gap.ofFont(p.getValue(), 0, 0, 0)); // invalidateMeasure, not setValidLayout(false): the outgap is read by the PARENT's layout, // and invalidating only the label left it where it was - "Slide it" did nothing (iPhone, // 17/10/2026). moving.invalidateMeasure(); Screen.repaint(); }); p.onComplete(() -> { moving.getStyle() .outgap(Gap.ZERO); moving.invalidateMeasure(); Screen.repaint(); }); p.start(); } private void togglePulse() { if (loop != null && loop.isRunning()) { loop.stop(); pulsing.getStyle() .textColor(Styles.captionColor); Screen.repaint(); return; } loop = new LoopAnimation(1.2f); loop.onUpdate(() -> { pulsing.getStyle() .textColor(ColorUtils.lerpColor(Styles.captionColor.color(), Styles.primaryColor.color(), loop.getValue())); Screen.repaint(); }); loop.start(); } /** * Stopping what this screen started. * *A loop has no end of its own — it runs until told otherwise. Leaving one running when the * screen closes gives you a component that repaints forever, holding its whole tree alive, and * the symptom is a frame rate that drops a little more with every screen the user visits.
*/ @Override public void onRemove() { super.onRemove(); if (loop != null) loop.stop(); } private void button(Component body, String text, Runnable r) throws Exception { Button b = new Button(text); b.onAction(c -> r.run()); body.add(LAY_AUTO, outgap(b, 0, 0, 0, 1.2f)); } private void head(Component body, int icone, String t, PalColor tom) throws Exception { body.add(LAY_AUTO, Tones.head(icone, t, tom)); } } ``` ## Shared scaffolding Not part of this recipe, but read by it: the base class every recipe inherits its top bar and scrolling body from. ### dev/cf/recipe/Recipe.java ```java package dev.cf.recipe; import dev.cf.*; import dev.crossfly.ui.*; import dev.crossfly.ui.graphics.*; import dev.crossfly.ui.layout.*; import dev.crossfly.ui.skin.*; import dev.crossfly.ui.style.*; import static dev.crossfly.ui.Widgets.*; /** * Base of a recipe: one screen that shows one thing, and nothing else. * *A recipe is not a sample. A sample shows a component with all its knobs; a recipe answers a * question somebody actually has — "how do I put a filter sheet over a list?", "how do I make this * follow the theme?" — in as few lines as it takes, so the answer can be read in one screen and * copied without editing.
* *That is the whole design constraint: the boilerplate lives here, the substance lives in the * subclass. A recipe that spends twenty lines building a title bar teaches the title bar.
* *Write one as:
* *
* public class MyRecipe extends Recipe
* {
* public String title() { return "What this shows"; }
* public String note() { return "The one sentence worth knowing."; }
*
* public void build(Component body) throws Exception
* {
* body.add(LAY_AUTO, new Button("Tap"));
* }
* }
*
*/
public abstract class Recipe extends SampleWindow implements Described
{
@Override
public abstract String title();
/**
* The one thing a reader should take away — printed above the recipe, in caption tone.
*
* @return the note, or null for none
*/
@Override
public String note()
{
return null;
}
/**
* Builds the recipe.
*
* @param body a vertical, scrollable container with sensible padding — add to it and stop
* @throws Exception when building fails
*/
public abstract void build(Component body) throws Exception;
@Override
public void onAdd(boolean firstTime) throws Exception
{
addTopBar(title());
// The page, not the surface. addTopBar just set fullscreenColor to the surface,
// and on a white page a white card has no edges — see Tones.page(). Re-derived on restyle so
// a dark-mode flip does not leave the light page behind.
fullscreenColor = Tones.page();
onRestyle(() -> fullscreenColor = Tones.page());
contents.setLayout(new VerticalLayout(Position.START, Position.START));
contents.getStyle()
.ingap(Gap.ofFont(1f, 1f, 1f, 1f));
String n = note();
if (n != null)
contents.add(LAY_AUTO, outgap(nota(n), 0, 0, 0, 1f));
Component body = new Component();
body.setLayout(new VerticalLayout(Position.START, Position.START));
body.setScrollable(ScrollDirection.VERTICAL);
body.testTag("recipe.body");
contents.add(LAY_FILL, body);
build(body);
if (pinned != null)
{
// Measured again once its labels have sizes: the band's AUTO height is taken in the first
// layout, before them, and on the iPhone it showed only its first line - the odometer's
// "No text recognizer on this device." was set and never seen (17/10/2026).
final Component band = pinned;
onUI(band::invalidateMeasure);
}
if (pinned != null)
body.add(LAY_AUTO, new Component()
{
@Override
public int getAutoHeight()
{
// Room for the last row to scroll clear of the floating band.
return pinned.getAutoHeight();
}
});
}
/**
* The note, as a tinted band rather than three lines of grey.
*
* It is the one sentence the reader is meant to leave with, and it used to be the least * legible thing on the screen: caption-coloured, caption-sized, indistinguishable from the * captions further down that are only labels. A tone and a glyph cost nothing here — nobody has * to read the band to know what it is.
* * @param n the note text * @return the band * @throws Exception when building fails */ /** * Pins {@code c} to the bottom of the screen, in a band that FLOATS over the scrolling body: it * stays on screen however far the body is scrolled, and the body scrolls underneath it. That is the * place a recipe says what just happened. An answer at the top of the body went out of view as soon * as the person scrolled down to the button that produced it (14/10/2026). *
* The band is 80% OPAQUE (the surface at alpha 0xCC), as the user asked; it floats rather than
* sitting below the body because a transparency with nothing behind it cannot be seen -- the first
* version had the band under the body, and the person saw a plain bar. The body gets a spacer as
* tall as the band at its end, so its last row can still scroll clear of it.
*
* @param c the component to pin, usually the answer label
* @return {@code c}, to chain
* @throws Exception if the layout refuses
*/
protected
* Provides common infrastructure:
*
*
*
* Usage
*
* public class MySample extends SampleWindow {
* public void onAdd(boolean firstTime) throws Exception {
* if (!firstTime) return;
* initWindow();
* addTopBar("My Sample");
* // ... add content
* }
* }
*
*/
public abstract class SampleWindow extends Window
{
/** The main content area of the window, added by {@link #addTopBar(String, Button...)}, for subclasses to add their content into. */
protected Component contents;
// ─── Top bar ─────────────────────────────────────────────────────────────
/**
* Builds and adds a standard top bar with a back (←) button on the left,
* a centered title, and any optional extra buttons on the right.
*
* @param title the text shown in the bar
* @param rightButtons zero or more icon buttons placed aligned to the right
* @throws Exception if component construction fails
*/
protected void addTopBar(String title, Button... rightButtons) throws Exception
{
fullscreenColor = Styles.backColor.color();
setLayout(new VerticalLayout());
add(0f, buildTopBar(title, rightButtons));
add(LAY_FILL, contents = new Component());
contents.getStyle()
.ingap(Gap.ofFont(0, .5f, 0, .5f));
}
/**
* Same as {@link #addTopBar(String, Button...)}, but returns the bar component
* instead of adding it, for callers that need to position it manually.
*
* @param title the bar title
* @param rightButtons optional right-side icon buttons
* @return the assembled top-bar {@link Component}
* @throws Exception if component construction fails
*/
protected Component buildTopBar(String title, Button... rightButtons) throws Exception
{
Button btBack = barButton("\ue5c4", this::hide); // arrow_back
btBack.testTag("sample.back");
// Padded on every side, like the bar's right buttons: with none above and below, the target
// was the arrow itself, too small to hit on a small phone (iPhone 5s, 17/10/2026).
btBack.getStyle()
.ingap(Gap.ofFont(.75f))
.outgap(Gap.ofFont(0, 0, .25f, 0));
Component bar = new Component().style(barStyle);
bar.setLayout(new GridLayout(Position.START, Position.CENTER));
int n = 2 + rightButtons.length;
Object[] params = new Object[n * 2];
params[0] = 0f;
params[1] = 1f;
for (int i = 0; i < rightButtons.length; i++)
params[2 + i] = 0f;
params[n] = btBack;
params[n + 1] = new Label(title).style(barTitleStyle);
for (int i = 0; i < rightButtons.length; i++)
{
params[n + 2 + i] = rightButtons[i];
rightButtons[i].getStyle()
.ingap(Gap.ofFont(.75f));
}
bar.add(params);
return bar;
}
/**
* Creates a standard bar icon button (transparent, white icon, pressed feedback).
*
* @param materialIcon the Material Icon unicode codepoint string
* @param action the action to run when the button is tapped
* @return the configured {@link Button}
*/
protected Button barButton(String materialIcon, Runnable action)
{
return new Button(new MaterialIcon(materialIcon)).style(barButtonNormal)
.pressedStyle(barButtonPressed)
.onAction(e -> action.run());
}
}
```