The pickers, and the callback shape they all share.
\n\nEvery picker is a Window that answers:\nshow(answer -> …), where answer is null when the user cancelled. One\nshape for date, time, colour, file, photo, barcode and location — so learning one is learning\nall of them.
Handle the null. Cancelling is not an error and not an edge case; it is the most common\noutcome of opening a picker by mistake, and a callback that assumes an answer throws on a path\nevery user takes.
\n\nFor a date inside a form, do not open a picker by hand at all — a TextField in\nEditMode.DATE opens it for you and writes the answer back. See R10Form.
Every picker is a {@link dev.crossfly.ui.Window} that answers:\n * {@code show(answer -> …)}, where {@code answer} is {@code null} when the user cancelled. One\n * shape for date, time, colour, file, photo, barcode and location — so learning one is learning\n * all of them.
\n *\n *Handle the null. Cancelling is not an error and not an edge case; it is the most common\n * outcome of opening a picker by mistake, and a callback that assumes an answer throws on a path\n * every user takes.
\n *\n *For a date inside a form, do not open a picker by hand at all — a {@code TextField} in\n * {@code EditMode.DATE} opens it for you and writes the answer back. See {@link R10Form}.
\n */\npublic class R20Pickers extends Recipe\n{\n private Label answer;\n\n public String title()\n {\n return \"Pickers\";\n }\n\n public String note()\n {\n return \"show(answer -> …) on all of them, and answer is null when the user backed out. The\"\n + \" ones needing hardware live in R21, and the system file picker in R31 — those can be\"\n + \" refused.\";\n }\n\n public void build(Component body) throws Exception\n {\n answer = label(\"Nothing picked yet.\", 1f, false, Styles.captionColor, Position.START);\n answer.testTag(\"pickers.answer\");\n // Pinned below the scrolling body, so the answer stays in view (see Recipe.pin).\n pin(answer);\n\n open(body, 0xE878, \"Date\", () -> new DatePicker().show(a -> said(\"Date\", a)));\n open(body, 0xE8B5, \"Time\", () -> new TimePicker().show(a -> said(\"Time\", a)));\n open(body, 0xE916, \"Date range\", () -> new DateRangePicker().show(a -> said(\"Range\", a)));\n open(body, 0xE40A, \"Colour\", () -> new ColorPicker(Styles.primaryColor.color())\n .show(a -> said(\"Colour\", a)));\n }\n\n /** A row per picker: its glyph on a tonal tile, its name, and the whole card opens it. */\n private void open(Component body, int icone, String name, Runnable go) throws Exception\n {\n Card c = new Card();\n c.setLayout(new GridLayout(Position.START, Position.CENTER));\n c.getStyle()\n .outgap(Gap.ofFont(0, 0, 0, .5f))\n .pressable();\n c.testTag(\"pickers.\" + name.toLowerCase()\n .replace(' ', '.'));\n c.onAction(e -> go.run());\n c.add(0f, 1f, 0f, Tones.tile(icone, Tones.accent()),\n outgap(label(name, 1.2f, true, Styles.textColor, Position.START), .6f, 0, 0, 0),\n matglyph(0xE5CC, tertiary(), 1f)); // chevron_right\n body.add(LAY_AUTO, c);\n }\n\n /** One place that handles the answer, including the null every picker can return. */\n private void said(String what, Object a)\n {\n answer.setText(a == null ? what + \": cancelled\" : what + \": \" + a);\n answer.invalidateMeasure(); // the pinned band must grow with it (see Recipe.pin)\n Screen.repaint();\n }\n}\n" } ], "lines": 84, "sharedFiles": [ { "path": "dev/cf/recipe/Recipe.java", "name": "Recipe.java", "code": "package dev.cf.recipe;\n\nimport dev.cf.*;\nimport dev.crossfly.ui.*;\nimport dev.crossfly.ui.graphics.*;\nimport dev.crossfly.ui.layout.*;\nimport dev.crossfly.ui.skin.*;\nimport dev.crossfly.ui.style.*;\n\nimport static dev.crossfly.ui.Widgets.*;\n\n/**\n * Base of a recipe: one screen that shows one thing, and nothing else.\n *\n *A recipe is not a sample. A sample shows a component with all its knobs; a recipe answers a\n * question somebody actually has — \"how do I put a filter sheet over a list?\", \"how do I make this\n * follow the theme?\" — in as few lines as it takes, so the answer can be read in one screen and\n * copied without editing.
\n *\n *That is the whole design constraint: the boilerplate lives here, the substance lives in the\n * subclass. A recipe that spends twenty lines building a title bar teaches the title bar.
\n *\n *Write one as:
\n *\n *\n * public class MyRecipe extends Recipe\n * {\n * public String title() { return \"What this shows\"; }\n * public String note() { return \"The one sentence worth knowing.\"; }\n *\n * public void build(Component body) throws Exception\n * {\n * body.add(LAY_AUTO, new Button(\"Tap\"));\n * }\n * }\n * \n */\npublic abstract class Recipe extends SampleWindow implements Described\n{\n @Override\n public abstract String title();\n\n /**\n * The one thing a reader should take away — printed above the recipe, in caption tone.\n *\n * @return the note, or null for none\n */\n @Override\n public String note()\n {\n return null;\n }\n\n /**\n * Builds the recipe.\n *\n * @param body a vertical, scrollable container with sensible padding — add to it and stop\n * @throws Exception when building fails\n */\n public abstract void build(Component body) throws Exception;\n\n @Override\n public void onAdd(boolean firstTime) throws Exception\n {\n addTopBar(title());\n\n // The page, not the surface. addTopBar just set fullscreenColor to the surface,\n // and on a white page a white card has no edges — see Tones.page(). Re-derived on restyle so\n // a dark-mode flip does not leave the light page behind.\n fullscreenColor = Tones.page();\n onRestyle(() -> fullscreenColor = Tones.page());\n\n contents.setLayout(new VerticalLayout(Position.START, Position.START));\n contents.getStyle()\n .ingap(Gap.ofFont(1f, 1f, 1f, 1f));\n\n String n = note();\n if (n != null)\n contents.add(LAY_AUTO, outgap(nota(n), 0, 0, 0, 1f));\n\n Component body = new Component();\n body.setLayout(new VerticalLayout(Position.START, Position.START));\n body.setScrollable(ScrollDirection.VERTICAL);\n body.testTag(\"recipe.body\");\n contents.add(LAY_FILL, body);\n build(body);\n if (pinned != null)\n {\n // Measured again once its labels have sizes: the band's AUTO height is taken in the first\n // layout, before them, and on the iPhone it showed only its first line - the odometer's\n // \"No text recognizer on this device.\" was set and never seen (17/10/2026).\n final Component band = pinned;\n onUI(band::invalidateMeasure);\n }\n if (pinned != null)\n body.add(LAY_AUTO, new Component()\n {\n @Override\n public int getAutoHeight()\n {\n // Room for the last row to scroll clear of the floating band.\n return pinned.getAutoHeight();\n }\n });\n }\n\n /**\n * The note, as a tinted band rather than three lines of grey.\n *\n * It is the one sentence the reader is meant to leave with, and it used to be the least\n * legible thing on the screen: caption-coloured, caption-sized, indistinguishable from the\n * captions further down that are only labels. A tone and a glyph cost nothing here — nobody has\n * to read the band to know what it is.
\n *\n * @param n the note text\n * @return the band\n * @throws Exception when building fails\n */\n /**\n * Pins {@code c} to the bottom of the screen, in a band that FLOATS over the scrolling body: it\n * stays on screen however far the body is scrolled, and the body scrolls underneath it. That is the\n * place a recipe says what just happened. An answer at the top of the body went out of view as soon\n * as the person scrolled down to the button that produced it (14/10/2026).\n *\n * The band is 80% OPAQUE (the surface at alpha 0xCC), as the user asked; it floats rather than\n * sitting below the body because a transparency with nothing behind it cannot be seen -- the first\n * version had the band under the body, and the person saw a plain bar. The body gets a spacer as\n * tall as the band at its end, so its last row can still scroll clear of it.\n *\n * @param c the component to pin, usually the answer label\n * @return {@code c}, to chain\n * @throws Exception if the layout refuses\n */\n protected \n * Provides common infrastructure:\n * \n *
\n *\n * Usage
\n * \n * public class MySample extends SampleWindow {\n * public void onAdd(boolean firstTime) throws Exception {\n * if (!firstTime) return;\n * initWindow();\n * addTopBar(\"My Sample\");\n * // ... add content\n * }\n * }\n * \n */\npublic abstract class SampleWindow extends Window\n{\n /** The main content area of the window, added by {@link #addTopBar(String, Button...)}, for subclasses to add their content into. */\n protected Component contents;\n\n // ─── Top bar ─────────────────────────────────────────────────────────────\n\n /**\n * Builds and adds a standard top bar with a back (←) button on the left,\n * a centered title, and any optional extra buttons on the right.\n *\n * @param title the text shown in the bar\n * @param rightButtons zero or more icon buttons placed aligned to the right\n * @throws Exception if component construction fails\n */\n protected void addTopBar(String title, Button... rightButtons) throws Exception\n {\n fullscreenColor = Styles.backColor.color();\n setLayout(new VerticalLayout());\n add(0f, buildTopBar(title, rightButtons));\n add(LAY_FILL, contents = new Component());\n contents.getStyle()\n .ingap(Gap.ofFont(0, .5f, 0, .5f));\n }\n\n /**\n * Same as {@link #addTopBar(String, Button...)}, but returns the bar component\n * instead of adding it, for callers that need to position it manually.\n *\n * @param title the bar title\n * @param rightButtons optional right-side icon buttons\n * @return the assembled top-bar {@link Component}\n * @throws Exception if component construction fails\n */\n protected Component buildTopBar(String title, Button... rightButtons) throws Exception\n {\n Button btBack = barButton(\"\\ue5c4\", this::hide); // arrow_back\n btBack.testTag(\"sample.back\");\n // Padded on every side, like the bar's right buttons: with none above and below, the target\n // was the arrow itself, too small to hit on a small phone (iPhone 5s, 17/10/2026).\n btBack.getStyle()\n .ingap(Gap.ofFont(.75f))\n .outgap(Gap.ofFont(0, 0, .25f, 0));\n\n Component bar = new Component().style(barStyle);\n bar.setLayout(new GridLayout(Position.START, Position.CENTER));\n\n int n = 2 + rightButtons.length;\n Object[] params = new Object[n * 2];\n params[0] = 0f;\n params[1] = 1f;\n for (int i = 0; i < rightButtons.length; i++)\n params[2 + i] = 0f;\n params[n] = btBack;\n params[n + 1] = new Label(title).style(barTitleStyle);\n for (int i = 0; i < rightButtons.length; i++)\n {\n params[n + 2 + i] = rightButtons[i];\n rightButtons[i].getStyle()\n .ingap(Gap.ofFont(.75f));\n }\n\n bar.add(params);\n return bar;\n }\n\n /**\n * Creates a standard bar icon button (transparent, white icon, pressed feedback).\n *\n * @param materialIcon the Material Icon unicode codepoint string\n * @param action the action to run when the button is tapped\n * @return the configured {@link Button}\n */\n protected Button barButton(String materialIcon, Runnable action)\n {\n return new Button(new MaterialIcon(materialIcon)).style(barButtonNormal)\n .pressedStyle(barButtonPressed)\n .onAction(e -> action.run());\n }\n}\n"
}
],
"page": "https://crossfly.dev/examples/pickers",
"run": "https://crossfly.dev/playground/index.html?ex=pickers",
"runLocally": "gradlew lwjgl3:run --args=\"classname dev.cf.recipe.R20Pickers\"",
"license": "See crossfly.dev for licensing. The code is published to be copied into your own project."
}