invokeLater – Clojure docs and tutorials

(See my full list of Clojure Swing examples and tutorials at Clojure Swing Interop)

When dealing with files, its very handy to use file dialogs. Here’s a quick example of using a JFileChooser to select a file to slurp and print.

Note the use of (into-array [“txt”]) as an argument to the FileNameExtensionFilter constructor. This is because the file extensions are provided as a String... meaning a java.lang.String array.

Also note, the .showOpenDialog call uses nil instead of a JFrame . We do that because we don’t have a JFrame showing that we want to associate the file dialog with.

(ns swingproject.core
  (:gen-class)
  (:import
    [javax.swing SwingUtilities JFileChooser]
    [ javax.swing.filechooser FileNameExtensionFilter]))

(defn slurp-file [java-file-object]
  (let [contents (slurp java-file-object)]
    (println contents)))

(defn slurp-a-thon
  []

  ;; opening and using a file dialog
  (SwingUtilities/invokeLater
    #(let [my-filter (FileNameExtensionFilter.
                       "Text file to slurp"
                       (into-array  ["txt"]))
           my-file-chooser (doto (JFileChooser.)
                             (.setFileFilter my-filter))
           selection-option (.showOpenDialog my-file-chooser nil)
           selection-file (.getSelectedFile my-file-chooser )
           ]
       (if (= selection-option JFileChooser/APPROVE_OPTION)
         (future (slurp-file selection-file)))))

  ;;giving the program some time to print before exiting
  (Thread/sleep 60000)
  (System/exit 0))

(defn -main
  "entry point for app"
  [& args]
  (slurp-a-thon))

(ns swingproject.core

(:gen-class)

(:import

[javax.swing SwingUtilities JFileChooser]

[ javax.swing.filechooser FileNameExtensionFilter]))

(defn slurp-file [java-file-object]

(let [contents (slurp java-file-object)]

(println contents)))

(defn slurp-a-thon

[]

;; opening and using a file dialog

(SwingUtilities/invokeLater

#(let [my-filter (FileNameExtensionFilter.

"Text file to slurp"

(into-array ["txt"]))

my-file-chooser (doto (JFileChooser.)

(.setFileFilter my-filter))

selection-option (.showOpenDialog my-file-chooser nil)

selection-file (.getSelectedFile my-file-chooser )

]

(if (= selection-option JFileChooser/APPROVE_OPTION)

(future (slurp-file selection-file)))))

;;giving the program some time to print before exiting

(Thread/sleep 60000)

(System/exit 0))

(defn -main

"entry point for app"

[& args]

(slurp-a-thon))

(See my full list of Clojure Swing examples and tutorials at Clojure Swing Interop)

Every complex GUI uses message dialogs. When using Clojure Swing interop, you will use the JOptionPane for your message dialogs. Two keys to remember when using JOptionPane s, is that they should always be called from within the Event Dispatch Thread (EDT). Sometimes the JOptionPane is shown by an ActionListener that is already on the EDT, and sometimes you need to call invokeAndWait , because your current thread is not the EDT.

The other key point to remember with JOptionPane s is that you can associate the message dialog with a frame, or set the frame to nil . If a JOptionPane ‘s frame is set to nil , then the message dialog will center itself on the screen when it displays. If a JFrame is provided to the JOptionPane , then the message dialog will center itself on the JFrame it is associated with.

Here is a basic example that provides a button to click, and that displays a plain JOptionPane with a message. The ActionListener is called from the EDT, so the JOptionPane is being called from the EDT.

(ns swingproject.core
  (:gen-class)
  (:import
    [javax.swing SwingUtilities JFrame JButton JOptionPane]
    [java.awt FlowLayout]
    [java.awt.event ActionListener]))

(defn create-and-show-gui
  []

  (let [my-frame (doto (JFrame. "JOptionPane Example")
                   (.setDefaultCloseOperation JFrame/EXIT_ON_CLOSE)
                   (.setLocationRelativeTo nil))
        my-button (JButton. "Click ME!")
        content-pane (doto (.getContentPane  my-frame)
                       (.setLayout (FlowLayout.)))]

    (.addActionListener my-button
                        (reify ActionListener
                          (actionPerformed [this e]
                            (JOptionPane/showMessageDialog
                              my-frame
                              "Betcha always wanted a message in a JOptionPane!"))))
    (.add content-pane my-button)

    (.pack my-frame)
    (.setSize my-frame 300 200)
    (.setVisible my-frame true)))

(defn -main
  "entry point for app"
  [& args]
  (SwingUtilities/invokeLater create-and-show-gui))

(ns swingproject.core

(:gen-class)

(:import

[javax.swing SwingUtilities JFrame JButton JOptionPane]

[java.awt FlowLayout]

[java.awt.event ActionListener]))

(defn create-and-show-gui

[]

(let [my-frame (doto (JFrame. "JOptionPane Example")

(.setDefaultCloseOperation JFrame/EXIT_ON_CLOSE)

(.setLocationRelativeTo nil))

my-button (JButton. "Click ME!")

content-pane (doto (.getContentPane my-frame)

(.setLayout (FlowLayout.)))]

(.addActionListener my-button

(reify ActionListener

(actionPerformed [this e]

(JOptionPane/showMessageDialog

my-frame

"Betcha always wanted a message in a JOptionPane!"))))

(.add content-pane my-button)

(.pack my-frame)

(.setSize my-frame 300 200)

(.setVisible my-frame true)))

(defn -main

"entry point for app"

[& args]

(SwingUtilities/invokeLater create-and-show-gui))

Here is an example that shows a JOptionPane that displays from a normal thread. The EDT must be explicitly called with invokeAndWait . The four most common types of message dialogs are shown.

(ns swingproject.core
  (:gen-class)
  (:import
    [javax.swing SwingUtilities JOptionPane]))

(defn example-message-dialogs
  []

  ;; Default message dialog
  (SwingUtilities/invokeAndWait
    #(JOptionPane/showMessageDialog
       nil
       "This is the default style"))

  ;; Plain message dialog
  (SwingUtilities/invokeAndWait
    #(JOptionPane/showMessageDialog
       nil
       "This is the 'plain' style message dialog"
       "My Plain Title"
       JOptionPane/PLAIN_MESSAGE))

  ;; Warning message dialog
  (SwingUtilities/invokeAndWait
    #(JOptionPane/showMessageDialog
       nil
       "I'm a 'warning' message dialog"
       "My Warning"
       JOptionPane/WARNING_MESSAGE))

  ;; Error message dialog
  (SwingUtilities/invokeAndWait
    #(JOptionPane/showMessageDialog
       nil
       "This is the 'error' message dialog"
       "My Error"
       JOptionPane/ERROR_MESSAGE))
  )

(defn -main
  "entry point for app"
  [& args]
  (example-message-dialogs))

(ns swingproject.core

(:gen-class)

(:import

[javax.swing SwingUtilities JOptionPane]))

(defn example-message-dialogs

[]

;; Default message dialog

(SwingUtilities/invokeAndWait

#(JOptionPane/showMessageDialog

nil

"This is the default style"))

;; Plain message dialog

(SwingUtilities/invokeAndWait

#(JOptionPane/showMessageDialog

nil

"This is the 'plain' style message dialog"

"My Plain Title"

JOptionPane/PLAIN_MESSAGE))

;; Warning message dialog

(SwingUtilities/invokeAndWait

#(JOptionPane/showMessageDialog

nil

"I'm a 'warning' message dialog"

"My Warning"

JOptionPane/WARNING_MESSAGE))

;; Error message dialog

(SwingUtilities/invokeAndWait

#(JOptionPane/showMessageDialog

nil

"This is the 'error' message dialog"

"My Error"

JOptionPane/ERROR_MESSAGE))

)

(defn -main

"entry point for app"

[& args]

(example-message-dialogs))

Tag: invokeLater

File Dialogs in Clojure

Clojure JOptionPane