Alert

Alert is CrossFly’s modal dialog box — the equivalent of a MessageBox/AlertDialog. It shows a title, a message (with automatic word-wrap) and one or more action buttons laid out in rows. Each button can have its own callback; without a callback, the button just closes the dialog. The visuals (colors, fonts, button layout) come from the active Skin.

🟢 · Package: dev.crossfly.ui · Extends: Window · Style: AlertStyle + WindowStyle

When to use

• Confirmations that require user acknowledgment (delete? save? discard?).
• Simple yes/no choices or a message that needs an “OK”.

When NOT to use

• Passive and ephemeral feedback (success/error/status) → use Hint.
• Contextual action list over an item (share/edit/delete) → use ActionSheet.

Appearance

A centered card with the title at the top, the message in the middle and a row of buttons at the bottom. By default the background is not dimmed — adjust WindowStyle.fadeBackground for the classic modal effect.

Complete example (copy, paste and run)

package com.exemplo;

import dev.crossfly.ui.*;
import dev.crossfly.ui.layout.*;

/** Runnable main screen. Point the launcher (classname) and run: gradlew :lwjgl3:run */
public class MainWindow extends Window
{
   @Override
   public void onShow() throws Exception
   {
      super.onShow();
      setLayout(new VerticalLayout());

      Button abrir = new Button("Abrir alerta");
      abrir.onAction(c ->
      {
         Alert a = new Alert("Excluir item",
            "Tem certeza que deseja excluir este item? Esta ação não pode ser desfeita.",
            "Excluir", "Cancelar");
         // Darkened background to reinforce the modality (alpha 0..255)
         WindowStyle ws = a.getStyle();
         ws.fadeBackground(150);
         // Button 0 = Delete -> executes, closes and gives feedback
         a.buttonAction(0, origin ->
         {
            a.hide();
            Hint.show("Item excluído", 2000);
         });
         // Button 1 = Cancel: no callback -> default already calls hide()
         a.show();
      });
      add(LAY_AUTO, abrir);
   }
}

The snippets below show only the core (what goes inside onShow()). To run them, place them in the MainWindow skeleton above.

Basic usage

// buttonTexts is optional varargs — if empty/null, becomes {"OK"}
Alert a = new Alert("Aviso", "Operação concluída com sucesso.", "OK");
a.show();

Constructors

⚠️ There is no static Alert.show(...) nor a constructor that fires a callback. Always instantiate with new Alert(...), register the per-button callbacks and call show().

Properties and customization

Callbacks and events

⚠️ The response does NOT come through show(onAnswer). Alert extends Window, not Picker — and Window.hide() only delivers onAnswer when this instanceof Picker. So, to react to each button, use buttonAction(index, action). There is no getAnswer() on Alert.

The callback type is Component.Action, whose method is void run(Component origin) — the lambda body does not return a value (no return null;).

States

• Button without a registered callback → receives the default action hide() (closes the dialog).
• Button with a callback → runs the callback; if the callback does not close it, the dialog stays open (call a.hide() yourself).
• “Back” gesture → honored if WindowStyle.canHide (default true).

Confirmation with dimmed background

Alert confirm = new Alert("Excluir item",
   "Tem certeza que deseja excluir este item? Esta ação não pode ser desfeita.",
   "Excluir", "Cancelar");

// Reinforces the modality by darkening the background (alpha 0..255)
WindowStyle ws = confirm.getStyle();
ws.fadeBackground(150);

// Button 0 = Delete -> executes, closes and gives feedback
confirm.buttonAction(0, origin ->
{
   excluirItem();
   confirm.hide();
   Hint.show("Item excluído", 2000);
});
// Button 1 = Cancel: no callback -> default already calls hide()

confirm.show();

Choose the button layout

Alert a = new Alert("Salvar", "Deseja salvar as alterações?", "Salvar", "Descartar");
a.style().buttonLayout(AlertStyle.ButtonLayout.IOS)  // IOS / FLUTTER / MATERIAL
         .maxButtonsPerRow(2);
a.show();

Best practices

• Use it for decisions that require acknowledgment. For passive feedback, prefer Hint.
• Keep few buttons — too many wrap into rows and make the dialog tall.
• Combine with fadeBackground whenever you want the classic modal effect.

Common mistakes

• Expecting a response via show(onAnswer) — that is exclusive to Picker. Register buttonAction(...).
• Accessing getButton(i) before show() — the buttons are created in onAdd and return null before that.
• Making the buttonAction lambda return a value — Action.run(...) is void.

See also

• Area guide: ui/ · Recipes: cookbook/
• Related components: ActionSheet · Hint