ScalaFX – Alerts and Dialogs
March 18, 2015
Posted by on One of the new features on ScalaFX 8.0.40 are Alerts and Dialogs. Dialog API allows for opening a dialog window and returning result from the user. The result can be as simple as the type of button used to close the dialog. Custom dialog allows for returning an arbitrary result.
We will present examples of ScalaFX Alerts and Dialogs based on examples presented in JavaFX Dialogs blog post.
Simple Alerts
Information Alert
There are several predefined dialogs called alerts that can be easily presented to the user. A simplest alert can be shown with a single line of code:
new Alert(AlertType.Information, "Hello Dialogs!!!").showAndWait()
In general use you will typically customize it a bit more:
new Alert(AlertType.Information) { initOwner(stage) title = "Information Dialog" headerText = "Look, an Information Dialog" contentText = "I have a great message for you!" }.showAndWait()
initOwner()
specifies the owner for a dialog. It is not required, but specifying an owner is a good style. It allows the dialog to use the same icon as the owner. It also will let block the parent when dialog is shown modal.
Warning Alert
new Alert(AlertType.Warning) { initOwner(stage) title = "Warning Dialog" headerText = "Look, an Warning Dialog." contentText = "Careful with the next step!" }.showAndWait()
Error Alert
new Alert(AlertType.Error) { initOwner(stage) title = "Error Dialog" headerText = "Look, an Error Dialog." contentText = "Ooops, there was an error!" }.showAndWait()
Confirmation Alert
Alerts and dialogs can be used to query user for information. Every alert returns type of button that was pressed to close the dialog window. A simplest form is a confirmation dialog that indicates whether user pressed OK
or Cancel
buttons. Strictly speaking a dialog returns an Option
containing type of button pressed or None
.
// Create and show confirmation alert val alert = new Alert(AlertType.Confirmation) { initOwner(stage) title = "Confirmation Dialog" headerText = "Look, a Confirmation Dialog." contentText = "Are you ok with this?" } val result = alert.showAndWait() // React to user's selectioon result match { case Some(ButtonType.OK) => println("OK") case _ => println("Cancel or closed") }
You can create a dialog returning any content, an example will be shown later. First let see how to use custom buttons in an alert.
Alerts with Custom Buttons
We can customize the button in an alert by defining ButtonType
objects and passing them to Alert’s buttonTypes
property. Notice that we overwrite the content of the property (rather than append to it):
val ButtonTypeOne = new ButtonType("One") val ButtonTypeTwo = new ButtonType("Two") val ButtonTypeThree = new ButtonType("Three") val alert = new Alert(AlertType.Confirmation) { initOwner(stage) title = "Confirmation Dialog with Custom Actions" headerText = "Look, a Confirmation Dialog with Custom Actions." contentText = "Choose your option." // Note that we override here default dialog buttons, OK and Cancel, with new ones. buttonTypes = Seq(ButtonTypeOne, ButtonTypeTwo, ButtonTypeThree, ButtonType.Cancel) } val result = alert.showAndWait() result match { case Some(ButtonTypeOne) => println("... user chose "One"") case Some(ButtonTypeTwo) => println("... user chose "Two"") case Some(ButtonTypeThree) => println("... user chose "Three"") case _ => println("... user chose CANCEL or closed the dialog") }
Alerts with Custom Content
You are not limited to simple text in an alert. You can add your custom content. For instance, there is no predefined Alert for showing exceptions, but you can add your own implementation:
// Create expandable Exception. val exceptionText = { val ex = new FileNotFoundException("Could not find file blabla.txt") val sw = new StringWriter() val pw = new PrintWriter(sw) ex.printStackTrace(pw) sw.toString } val label = new Label("The exception stacktrace was:") val textArea = new TextArea { text = exceptionText editable = false wrapText = true maxWidth = Double.MaxValue maxHeight = Double.MaxValue vgrow = Priority.Always hgrow = Priority.Always } val expContent = new GridPane { maxWidth = Double.MaxValue add(label, 0, 0) add(textArea, 0, 1) } new Alert(AlertType.Error) { initOwner(stage) title = "Exception Dialog" headerText = "Look, an Exception Dialog." contentText = "Could not find file blabla.txt!" // Set expandable Exception into the dialog pane. dialogPane().expandableContent = expContent }.showAndWait()
Text Input Dialog
You can get simple text input using the TextInputDialog
. It works similar to alerts, but it returns an Option
containing the text entered by the use (alerts return the button pressed):
val dialog = new TextInputDialog(defaultValue = "walter") { initOwner(stage) title = "Text Input Dialog" headerText = "Look, a Text Input Dialog." contentText = "Please enter your name:" } val result = dialog.showAndWait() result match { case Some(name) => println("Your name: " + name) case None => println("Dialog was canceled.") }
Choice Dialog
There is also a predefined dialog for selecting from a list of available choices: ChoiceDialog
.The list can be collection of arbitrary objects. The choice dialog will return Option
selected by the user. You create the dialog by specifying default choice and the collection of available choices.
val choices = Seq("a", "b", "c") val dialog = new ChoiceDialog(defaultChoice = "b", choices = choices) { initOwner(stage) title = "Choice Dialog" headerText = "Look, a Choice Dialog." contentText = "Choose your letter:" } val result = dialog.showAndWait() result match { case Some(choice) => println("Your choice: " + choice) case None => println("No selection") }
Custom Dialog
Custom dialogs are created using Dialog class. Below is an example of a login dialog. Class Result
defines result returned by the dialog. The dialog contains a custom graphic, two input fields (“Username” and “Password”), and custom buttons (“Login” and “Cancel”).
case class Result(username: String, password: String) // Create the custom dialog. val dialog = new Dialog[Result]() { initOwner(stage) title = "Login Dialog" headerText = "Look, a Custom Login Dialog" } // Set the button types. val loginButtonType = new ButtonType("Login", ButtonData.OKDone) dialog.dialogPane().buttonTypes = Seq(loginButtonType, ButtonType.Cancel) // Create the username and password labels and fields. val username = new TextField() { promptText = "Username" } val password = new PasswordField() { promptText = "Password" } val grid = new GridPane() { hgap = 10 vgap = 10 padding = Insets(20, 100, 10, 10) add(new Label("Username:"), 0, 0) add(username, 1, 0) add(new Label("Password:"), 0, 1) add(password, 1, 1) } // Enable/Disable login button depending on whether a username was entered. val loginButton = dialog.dialogPane().lookupButton(loginButtonType) loginButton.disable = true // Do some validation (disable when username is empty). username.text.onChange { (_, _, newValue) => loginButton.disable = newValue.trim().isEmpty } dialog.dialogPane().content = grid // Request focus on the username field by default. Platform.runLater(username.requestFocus()) // When the login button is clicked, convert the result to a username-password-pair. dialog.resultConverter = dialogButton => if (dialogButton == loginButtonType) Result(username.text(), password.text()) else null val result = dialog.showAndWait() result match { case Some(Result(u, p)) => println("Username=" + u + ", Password=" + p) case None => println("Dialog returned: None") }
Summary
ScalaFX 8.0.40-R8 brings support for Alerts and Dialogs. There are several predefined dialogs: Information, Warning, Error, Confirmation, Text Input, and Choice. Predefined dialog allow some level of customization of their content and buttons. Source code for the examples of pre-defined dialogs, including customization, are in DialogsDemo.
Completely customized dialogs can be created using Dialog
class. Source code for a custom login dialog is in LoginDialogDemo.
To use ScalaFX 8.0.40 add following to your SBT:
libraryDependencies += "org.scalafx" %% "scalafx" % “8.0.40-R8”
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