Setting the Stage (Creating a User Interface in JavaFX) Part 2

Obtaining Program Arguments

The first new concept introduced by this program is the ability to read the arguments passed into a JavaFX program. The javafx.application package includes a class named Application that has application lifecycle related methods such as launch(), init(), start(), and stop(). Another method in the Application class is getParameters(), which gives the application access to the arguments passed on the command-line, as well as unnamed parameters and <name,value> pairs specified in a JNLP file. Here’s the relevant code snippet from Listing 2-1 for your convenience:

Setting the Style of the Stage

We’re using the getParameters() method described previously to get an argument that tells us whether the stage style of the Stage instance should be its default (StageStyle.DECORATED), StageStyle.UNDECORATED, or StageStyle.TRANSPARENT. You saw the effects of each in the preceding exercise, specifically in Figures 2-2, 2-4, and 2-5.

Controlling Whether a Stage Is Resizable

As shown in the snippet below from Listing 2-1, to make this application’s window initially resizable we’re calling the setResizable() method of the Stage instance. To keep the resizable property of the Stage and the state of the resizable check box synchronized, the check box is bidirectionally bound to the resizable property of the Stage instance.

■ Tip A property that is bound cannot be explicitly set. In the code preceding the snippet, the resizable property is set with the setResizable() method before the property is bound in the next line.

Making a Stage Full Screen

Making the Stage show in full-screen mode is done by setting the fullScreen property of the Stage instance to true. As shown in the snippet below from Listing 2-1, to keep the fullScreen property of the Stage and the state of the fullScreen check box synchronized, the fullScreen property of the Stage instance is updated whenever the selected property of the checkBox changes.

Working with the Bounds of the Stage

The bounds of the Stage are represented by its x, y, width, and height properties whose values can be changed at will. This is demonstrated in the following snippet from Listing 2-1 where the Stage is placed near the top and centered horizontally on the primary screen after the Stage has been initialized.

We’re using the Screen class of the javafx.stage package to get the dimensions of the primary screen so that the desired position may be calculated.

■ Note We intentionally made the Stage in Figure 2-2 larger than the Scene contained within to make the following point. The width and height of a Stage include its decorations (title bar and border), which vary on different platforms. It is therefore usually better to control the width and height of the Scene (we show you how in a bit) and let the Stage conform to that size.

Drawing Rounded Rectangles

The following snippet from Listing 2-1 draws the sky-blue rounded rectangle that becomes the background for the transparent window example in Figure 2-5.

Dragging the Stage on the Desktop When a Title Bar Isn’t Available

The Stage may be dragged on the desktop using its title bar, but in the case where its StageStyle is UNDECORATED or TRANSPARENT, the title bar isn’t available. To allow dragging in this circumstance, we added the code shown in the following code snippet from Listing 2-1.

Event handlers are covered a little later in the topic, but as a preview, the handle() method of the anonymous class that is supplied to the onMouseDragged() method is called when the mouse is dragged. As a result, the values of the x and y properties are altered by the number of pixels that the mouse was dragged, which moves the Stage as the mouse is dragged.

Using UI Layout Containers

When developing applications that will be deployed in a cross-platform environment or are internationalized, it is good to use layout containers. One advantage of using layout containers is that when the node sizes change, their visual relationships with each other are predictable. Another advantage is that you don’t have to calculate the location of each node that you place in the UI.

The following snippet from Listing 2-1 shows how the VBox layout class, located in the javafx.scene.layout package, is used to arrange the Text, CheckBox, HBox, and Button nodes in a column. This snippet also shows that layout containers may be nested, as demonstrated by the HBox that arranges the Label and TextField nodes horizontally. Note that several lines of code are omitted from this snippet in order to see the layout nesting clearly:

 

 

 

 

Unlike the Group class, the VBox class arranges its contained nodes vertically, spacing them apart from each other by the number of pixels specified in the spacing property.

Ascertaining Whether the Stage Is in Focus

To know whether your JavaFX application is the one that currently is in focus (e.g., keys pressed are delivered to the application), simply consult the focused property of the Stage instance. The following snippet from Listing 2-1 demonstrates this.

Controlling the Z-Order of the Stage

In the event that you want your JavaFX application to appear on top of other windows or behind other windows onscreen, you can use the toFront() and toBack() methods, respectively. The following snippet from Listing 2-1 shows how this is accomplished.

Closing the Stage and Detecting When It Is closed

As shown in the following code snippet from Listing 2-1, you can programmatically close the Stage with its close() method. This is important when the stageStyle is undecorated or transparent, because the close button supplied by the windowing system is not present.

By the way, you can detect when there is an external request to close the Stage by using the onCloseRequest event handler as shown in the following code snippet from Listing 2-1.

To see this in action, run the application without any arguments so that it has the appearance of Figure 2-2 shown previously, and then click the close button on the decoration of the window.

■ Tip The onCloseRequest event handler is only called when there is an external request to close the window. This is why the "Stage is closing" message doesn’t appear in this example when you click the button labeled "close()".