JavaFX Stage

港控/mmm° 2023-10-14 18:57 14阅读 0赞

A JavaFX *Stage*, `javafx.stage.Stage`, represents a window in a JavaFX desktop application. Inside a JavaFX `Stage` you can insert a JavaFX `Scene` which represents the content displayed inside a window - inside a `Stage`.

When a JavaFX application starts up, it creates a root `Stage` object which is passed to the `start(Stage primaryStage)` method of the root class of your JavaFX application. This `Stage` object represents the primary window of your JavaFX application. You can create new `Stage` objects later in your application's life time, in case your application needs to open more windows.

## Creating a Stage ##

You create a JavaFX `Stage` object just like any other Java object: Using the `new` command and the `Stage` constructor. Here is an example of creating a JavaFX `Stage` object.

Stage stage = new Stage();

### Showing a Stage ###

Simple creating a JavaFX `Stage` object will not show it. In order to make the `Stage` visible you must call either its `show()` or `showAndWait()` method. Here is an example of showing a JavaFX `Stage`:

Stage stage = new Stage();
    stage.show();

#### show() vs. showAndWait() ####

The difference between the JavaFX `Stage` methods `show()` and `showAndWait()` is, that `show()` makes the `Stage` visible and the exits the `show()` method immediately, whereas the `showAndWait()` shows the `Stage` object and then blocks (stays inside the `showAndWait()` method) until the `Stage` is closed.

### Set a Scene on a Stage ###

In order to display anything inside a JavaFX `Stage`, you must set a JavaFX `Scene` object on the `Stage`. The content of the `Scene` will then be displayed inside the `Stage` when the `Stage` is shown. Here is an example of setting a `Scene` on a JavaFX `Stage`:

VBox vBox = new VBox(new Label("A JavaFX Label"));
    Scene scene = new Scene(vBox);
    
    Stage stage = new Stage();
    stage.setScene(scene);

### Stage Title ###

You can set the JavaFX `Stage` title via the `Stage` `setTitle()` method. The `Stage` title is displayed in the title bar of the `Stage` window. Here is an example of setting the title of a JavaFX `Stage`:

stage.setTitle("JavaFX Stage Window Title");

### Stage Position ###

You can set the position (X,Y) of a JavaFX `Stage` via its `setX()` and `setY()` methods. The `setX()` and `setY()` methods set the position of the upper left corner of the window represented by the `Stage`. Here is an example of setting the X and Y position of a JavaFX `Stage` object:

Stage stage = new Stage();
    
    stage.setX(50);
    stage.setY(50);

Please note, that it might be necessary to also set the width and height of the `Stage` if you set the X and Y position, or the stage window might become very small. See the next section for more information about setting the width and height of a `Stage`.

### Stage Width and Height ###

You can set the width and of a JavaFX `Stage` via its `setWidth()` and `setHeight()` methods. Here is an example of setting the width and height of a JavaFX `Stage`:

Stage stage = new Stage();
    
    stage.setWidth(600);
    stage.setHeight(300);

### Stage Modality ###

You can set window modality of a JavaFX `Stage`. The `Stage` modality determines if the window representing the `Stage` will block other windows opened by the same JavaFX application. You set the window modality of a JavaFX `Stage` via its `initModality()` method. Here is an example of setting the JavaFX `Stage` modality:

public class StageExamples extends Application {
        public static void main(String[] args) {
            launch(args);
        }
    
        @Override
        public void start(Stage primaryStage) {
            primaryStage.setTitle("JavaFX App");
    
            Stage stage = new Stage();
            stage.initModality(Modality.APPLICATION_MODAL);
            //stage.initModality(Modality.WINDOW_MODAL);
            //stage.initModality(Modality.NONE);
    
            primaryStage.show();
    
            stage.showAndWait();
    
        }
    }

Notice how this example is a full JavaFX application. The `start()` method is executed when the JavaFX application is launched (first `main()` is called which calls `launch()` which later calls `start()`).

Notice also, how a new JavaFX `Stage` object is created, its modality mode set, and then both the primary and the new `Stage` objects are made visible (shown). The second `Stage` has its modality set to `Modality.APPLICATION_MODAL` meaning it will block all other windows (stages) opened by this JavaFX application. You cannot access any other windows until this `Stage` window has been closed.

The `Modality.WINDOW_MODAL` modality option means that the newly created `Stage` will block the `Stage` window that "owns" the newly created `Stage`, but only that. Not all windows in the application. See the next section below to see how to set the "owner" of a `Stage`.

The `Modality.NONE` modality option means that this `Stage` will not block any other windows opened in this application.

The `Modality.APPLICATION_MODAL` and `Modality.WINDOW_MODAL` modality modes are useful for `Stage` objects representing windows that function as "wizards" or "dialogs" which should block the application or window until the wizard or dialog process is completed by the user. The `Modality.NONE` modality is useful for `Stage` objects representing windows that can co-exist, like different browser windows in a browser application.

### Stage Owner ###

A JavaFX `Stage` can be *owned* by another `Stage`. You set the owner of a `Stage` via its `initOwner()` method. Here is an example of initializing the owner of a JavaFX `Stage`, plus set the modality of the `Stage` to `Modality.WINDOW_MODAL`:

public class StageExamples extends Application {
        public static void main(String[] args) {
            launch(args);
        }
    
        @Override
        public void start(Stage primaryStage) {
            primaryStage.setTitle("JavaFX App");
    
            Stage stage = new Stage();
            stage.initModality(Modality.WINDOW_MODAL);
    
            stage.initOwner(primaryStage);
    
            primaryStage.show();
    
            stage.showAndWait();
        }
    }

This example will open a new `Stage` which will block the `Stage` owning the newly created `Stage` (which is set to the primary stage).

### Stage Style ###

You can set the style of a JavaFX `Stage` via its `initStyle()` method. There are a set of different styles you can choose from:

DECORATED
        UNDECORATED
        TRANSPARENT
        UNIFIED
        UTILITY

A decorated `Stage` is a standard window with OS decorations (title bar and minimize / maximize / close buttons), and a white background.

An undecorated `Stage` is a standard window without OS decorations, but still with a white background.

A transparent `Stage` is an undecorated window with transparent background.

A unified `Stage` is like a decorated stage, except it has no border between the decoration area and the main content area.

A utility `Stage` is a decorated window, but with minimal decorations.

Here is an example of setting the style of a JavaFX `Stage`:

stage.initStyle(StageStyle.DECORATED);
    
    //stage.initStyle(StageStyle.UNDECORATED);
    //stage.initStyle(StageStyle.TRANSPARENT);
    //stage.initStyle(StageStyle.UNIFIED);
    //stage.initStyle(StageStyle.UTILITY);

Only the first line is actually executed. The rest are commented out. They are just there to show how to configure the other options.

### Stage Full Screen Mode ###

You can switch a JavaFX `Stage` into full screen mode via the `Stage` `setFullScreen()` method. Please note, that you may not get the expected result (a window in full screen mode) unless you set a `Scene` on the `Stage`. Here is an example of setting a JavaFX Stage to full screen mode:

VBox vbox = new VBox();
    Scene scene = new Scene(vbox);
    
    primaryStage.setScene(scene);
    primaryStage.setFullScreen(true);
    
    primaryStage.show();

### Stage Life Cycle Events ###

The JavaFX Stage can emit a few events you can listen for. These Stage events are:

*  Close Request
 *  Hiding
 *  Hidden
 *  Showing
 *  Shown

#### Close Stage Event Listener ####

You can listen for close events on a JavaFX Stage, meaning you can be notified when the user clicks the button with the X on, in the upper right corner of the Stage window. Listening for the Stage close event can be useful if you need to clean up some resources after the main Stage window is closed, or e.g. need to stop some threads etc. Here is an example of listening for Stage close events:

primaryStage.setOnCloseRequest((event) -> {
        System.out.println("Closing Stage");
    });

#### Hiding Stage Event Listener ####

You can attach a Stage hiding event listener to a JavaFX stage. The Stage hiding event listener is called before the Stage is being hidden, but after it has been requested hidden. Here is an example of attaching a Stage hiding event listener to a JavaFX Stage:

primaryStage.setOnHiding((event) -> {
        System.out.println("Hiding Stage");
    });

#### Hidden Stage Event Listener ####

You can attach a Stage hidden event listener to a JavaFX stage. The Stage hidden event listener is called after the Stage is hidden. Here is an example of attaching a Stage hidden event listener to a JavaFX Stage:

primaryStage.setOnHidden((event) -> {
        System.out.println("Stage hidden");
    });

#### Showing Stage Event Listener ####

You can attach a Stage showing event listener to a JavaFX stage. The Stage showing event listener is called after the Stage is requested shown, but before the Stage is shown. Here is an example of attaching a Stage showing event listener to a JavaFX Stage:

primaryStage.setOnShowing((event) -> {
        System.out.println("Showing Stage");
    });

#### Shown Stage Event Listener ####

You can attach a Stage shown event listener to a JavaFX stage. The Stage shown event listener is called after the Stage is shown. Here is an example of attaching a Stage shown event listener to a JavaFX Stage:

primaryStage.setOnShown((event) -> {
        System.out.println("Stage Shown");
    });

### Stage Keyboard Events ###

It is possible to listen for keyboard events on a JavaFX Stage. That way you can catch all keyboard events that occur while the Stage has focus. Here is an example that listens for the ESC and Return keys on the keyboard - when a JavaFX Stage has focus:

primaryStage.addEventHandler(KeyEvent.KEY_PRESSED,  (event) -> {
        System.out.println("Key pressed: " + event.toString());
    
        switch(event.getCode().getCode()) {
            case 27 : { // 27 = ESC key
                primaryStage.close();
                break;
            }
            case 10 : { // 10 = Return
                primaryStage.setWidth( primaryStage.getWidth() * 2);
            }
            default:  {
                System.out.println("Unrecognized key");
            }
        }
    });

转载：[JavaFX Stage][]

[JavaFX Stage]: https://jenkov.com/tutorials/javafx/stage.html