File Dialogs in Clojure

On: April 7, 2021April 7, 2021 By: cljdude

(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))

Clojure JOptionPane

On: April 7, 2021April 7, 2021 By: cljdude

(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))

Clojure Swing: Invoke Later

On: April 3, 2021April 6, 2021 By: cljdude

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

When developing Swing GUIs for Clojure, understanding and using SwingUtilities/invokeLater is crucial.

Event Dispatch Thread

Don’t confuse “thread” in this case with Clojure threading macros such as -> and --> . Threading here refers to concurrency.

Swing GUI components are not safe to access concurrently. If two threads modify the same Swing component at the same time, the result is unpredictable. Java solved this problem by introducing the event dispatch thread. All modification Swing displays and component values should happen on the event dispatch thread.

There is only one event dispatch thread. You access it by creating a Java Runnable and passing it to SwingUtilities/invokeLater . Lucky for us, all Clojure functions are Java Runnables. Here’s the general format.

(defn my-gui-modifier []
  ;; Do some Swing changes here
  )

(defn modit []
  (SwingUtilities/invokeLater my-gui-modifier))

(defn my-gui-modifier []

;; Do some Swing changes here

)

(defn modit []

(SwingUtilities/invokeLater my-gui-modifier))

Warning

Remember, ALL the screen rendering and modifications to your Swing components happen on the event dispatch thread. That means, if you tie up the event dispatch thread doing something time consuming, your app will appear to hang. This creates a horrible user experience. Any runnables you create should complete quickly.

On a somewhat related note, any time a Swing component alerts you to an event or a value change, you will want to hand back that thread immediately and use a new thread to do any long tasks associated with the notifications.