Cljfx

受 react 和 re-frame 的启发,JavaFX 的声明式、功能性和可扩展的封装器。「Declarative, functional and extensible wrapper of JavaFX inspired by better parts of react and re-frame」

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Cljfx is a declarative, functional and extensible wrapper of JavaFX
inspired by better parts of react and re-frame.

Rationale

I wanted to have an elegant, declarative and composable UI
library for JVM and couldn't find one. Cljfx is inspired by react,
reagent, re-frame and fn-fx.

Like react, it allows to specify only desired layout, and handles
all actual changes underneath. Unlike react (and web in general) it does
not impose xml-like structure of everything possibly having multiple
children, thus it uses maps instead of hiccup for describing layout.

Like reagent, it allows to specify component descriptions using simple
constructs such as data and functions. Unlike reagent, it rejects using
multiple stateful reactive atoms for state and instead prefers composing
ui in more pure manner.

Like re-frame, it provides an approach to building large applications
using subscriptions and events to separate view from logic. Unlike
re-frame, it has no hard-coded global state, and subscriptions work on
referentially transparent values instead of ever-changing atoms.

Like fn-fx, it wraps underlying JavaFX library so developer can describe
everything with clojure data. Unlike fn-fx, it is more dynamic, allowing
users to use maps and functions instead of macros and deftypes, and has
more explicit and extensible lifecycle for components.

Installation and requirements

Cljfx uses tools.deps, so you can add this repo with latest sha as a
dependency:

 cljfx {:git/url "https://github.com/cljfx/cljfx" :sha "<insert-sha-here>"}

Cljfx is also published on Clojars, so you can add cljfx as a maven
dependency, current version is on this badge:

Cljfx on Clojars

Minimum required version of clojure is 1.10.

When depending on git coordinates, minimum required Java version is 11. When using maven
dependency, both Java 8 (assumes it has JavaFX provided in JRE) and Java 11 (via openjfx
dependency) are supported. You don't need to configure anything in this regard: correct
classifiers are picked up automatically.

Please note that JavaFX 8 is outdated and has problems some people consider severe: it
does not support HiDPI scaling on Linux, and sometimes crashes JVM on macOS Mojave. You
should prefer JDK 11.

Overview

Hello world

Components in cljfx are described by maps with :fx/type key. By
default, fx-type can be:

  • a keyword corresponding to some JavaFX class
  • a function, which receives this map as argument and returns
    another description
  • an implementation of Lifecycle protocol (more on that in extending
    cljfx
    section)

Minimal example:

(ns example
  (:require [cljfx.api :as fx]))

(fx/on-fx-thread
  (fx/create-component
    {:fx/type :stage
     :showing true
     :title "Cljfx example"
     :width 300
     :height 100
     :scene {:fx/type :scene
             :root {:fx/type :v-box
                    :alignment :center
                    :children [{:fx/type :label
                                :text "Hello world"}]}}}))

Evaluating this code will create and show a window:

The overall mental model of these descriptions is this:

  • whenever you need a JavaFX class, use map where :fx/type key has a
    value of a kebab-cased keyword derived from that class name
  • other keys in this map represent JavaFX properties of that class (also
    in kebab-case);
  • if prop x can be changed by user, there is a corresponding
    :on-x-changed prop for observing these changes

Renderer

To be truly useful, there should be some state and changes over time,
for this matter there is a renderer abstraction, which is a function
that you may call whenever you want with new description, and cljfx will
advance all the mutable state underneath to match this description.
Example:

(def renderer
  (fx/create-renderer))

(defn root [{:keys [showing]}]
  {:fx/type :stage
   :showing showing
   :scene {:fx/type :scene
           :root {:fx/type :v-box
                  :padding 50
                  :children [{:fx/type :button
                              :text "close"
                              :on-action (fn [_]
                                           (renderer {:fx/type root
                                                      :showing false}))}]}}})

(renderer {:fx/type root
           :showing true})

Evaluating this code will show this:

Clicking close button will hide this window.

Renderer batches descriptions and re-renders views on fx thread only
with last received description, so it is safe to call many times at
once. Calls to renderer function return derefable that will contain
component value with most recent description.

Atoms

Example above works, but it's not very convenient: what we'd really like
is to have a single global state as a value in an atom, derive our
description of JavaFX state from this value, and change this atom's
contents instead. Here is how it's done:

;; Define application state

(def *state
  (atom {:title "App title"}))

;; Define render functions

(defn title-input [{:keys [title]}]
  {:fx/type :text-field
   :on-text-changed #(swap! *state assoc :title %)
   :text title})

(defn root [{:keys [title]}]
  {:fx/type :stage
   :showing true
   :title title
   :scene {:fx/type :scene
           :root {:fx/type :v-box
                  :children [{:fx/type :label
                              :text "Window title input"}
                             {:fx/type title-input
                              :title title}]}}})

;; Create renderer with middleware that maps incoming data - description -
;; to component description that can be used to render JavaFX state.
;; Here description is just passed as an argument to function component.

(def renderer
  (fx/create-renderer
    :middleware (fx/wrap-map-desc assoc :fx/type root)))

;; Convenient way to add watch to an atom + immediately render app

(fx/mount-renderer *state renderer)

Evaluating code above pops up this window:

Editing input then immediately updates displayed app title.

Map events

Consider this example:

(defn todo-view [{:keys [text id done]}]
  {:fx/type :h-box
   :children [{:fx/type :check-box
               :selected done
               :on-selected-changed #(swap! *state assoc-in [:by-id id :done] %)
              {:fx/type :label
               :style {:-fx-text-fill (if done :grey :black)}
               :text text}]})

There are problems with using functions as event handlers:

  1. Performing mutation from these handlers requires coupling with that
    state, thus making todo-view dependent on mutable *state
  2. Updating state from listeners complects logic with view, making
    application messier over time
  3. There are unnecessary reassignments to on-selected-changed:
    functions have no equality semantics other than their identity, so on
    every change to this view (for example, when changing it's text),
    on-selected-changed will be replaced with another function with same
    behavior.

To mitigate these problems, cljfx allows to define event handlers as
arbitrary maps, and provide a function to a renderer that performs
actual handling of these map-events (with additional :fx/event key
containing dispatched event):

;; Define view as just data

(defn todo-view [{:keys [text id done]}]
  {:fx/type :h-box
   :spacing 5
   :padding 5
   :children [{:fx/type :check-box
               :selected done
               :on-selected-changed {:event/type ::set-done :id id}}
              {:fx/type :label
               :style {:-fx-text-fill (if done :grey :black)}
               :text text}]})

;; Define single map-event-handler that does mutation

(defn map-event-handler [event]
  (case (:event/type event)
    ::set-done (swap! *state assoc-in [:by-id (:id event) :done] (:fx/event event))))

;; Provide map-event-handler to renderer as an option

(fx/mount-renderer
  *state
  (fx/create-renderer
    :middleware (fx/wrap-map-desc assoc :fx/type root)
    :opts {:fx.opt/map-event-handler map-event-handler}))

You can see full example at examples/e09_todo_app.clj.

Interactive development

Another useful aspect of renderer function that should be used during
development is refresh functionality: you can call renderer function
with zero args and it will recreate all the components with current
description.

See walk-through in examples/e12_interactive_development.clj
as an example of how to iterate on cljfx app in REPL.

Special keys

Sometimes components accept specially treated keys. Main uses are:

  1. Reordering of nodes (instead of re-creating them) in parents that may
    have many children. Descriptions that have :fx/key during
    advancing get reordered instead of recreated if their position in
    child list is changed. Consider this example:

    (let [component-1 (fx/create-component
                        {:fx/type :v-box
                         :children [{:fx/type :label
                                     :fx/key 1
                                     :text "- buy milk"}
                                    {:fx/type :label
                                     :fx/key 2
                                     :text "- buy socks"}]})
          [milk-1 socks-1] (vec (.getChildren (fx/instance component-1)))
          component-2 (fx/advance-component
                        component-1
                        {:fx/type :v-box
                         :children [{:fx/type :label
                                     :fx/key 2
                                     :text "- buy socks"}
                                    {:fx/type :label
                                     :fx/key 1
                                     :text "- buy milk"}]})
          [socks-2 milk-2] (vec (.getChildren (fx/instance component-2)))]
      (and (identical? milk-1 milk-2)
           (identical? socks-1 socks-2)))
    => true
    

    With :fx/key-s specified, advancing of this component reordered
    children of VBox, and didn't change text of any labels, because their
    descriptions stayed the same.

  2. Providing extra props available in certain contexts. If node is
    placed inside a pane, pane can layout it differently by looking into
    properties map of a node. Nodes placed in ButtonBar can have
    OS-specific ordering depending on assigned ButtonData. These
    properties can be specified via keywords namespaced by container's
    fx-type. Example:

    (fx/on-fx-thread
      (fx/create-component
        {:fx/type :stage
         :showing true
         :scene {:fx/type :scene
                 :root {:fx/type :stack-pane
                        :children [{:fx/type :rectangle
                                    :width 200
                                    :height 200
                                    :fill :lightgray}
                                   {:fx/type :label
                                    :stack-pane/alignment :bottom-left
                                    :stack-pane/margin 5
                                    :text "bottom-left"}
                                   {:fx/type :label
                                    :stack-pane/alignment :top-right
                                    :stack-pane/margin 5
                                    :text "top-right"}]}}}))
    

    Evaluating code above produces this window:

    For a more complete example of available pane keys, see
    examples/e07_extra_props.clj

Factory props

There are some props in JavaFX that represent not a value, but a way to
construct a value from some input:

  • :page-factory in pagination, you can use function receiving page
    index and returning any component description for this prop (see
    example in examples/e06_pagination.clj)
  • various versions of :cell-factory in controls designed to display
    multiples of items (table views, list views etc.). You can use
    functions that receive items and return descriptions for these props,
    but they are a bit different: created cells have their own lifecycle
    for performance reasons, and that imposes a restriction that you can't
    specify :fx/type in returned cell descriptions. There are various
    usage examples available in
    examples/e16_cell_factories.clj

Subscriptions and contexts

Once application becomes complex enough, you can find yourself passing
very big chunks of state everywhere. Consider this example: you develop
a task tracker for an organization. A typical task view on a dashboard
displays a description of that task and an assignee. Required state for
this view is plain and simple, just a simple data like that:

{:title "Fix NPE on logout during full moon"
 :state :todo
 :assignee {:id 42 :name "Fred"}}

Then one day comes a requirement: users of this task tracker should be
able to change assignee from the dashboard. Now, we need a combo-box
with all assignable users to render such a view, and required data becomes
this:

{:title "Fix NPE on logout during full moon"
 :state :todo
 :assignee {:id 42 :name "Fred"}
 :users [{:id 42 :name "Fred"}
         {:id 43 :name "Alice"}
         {:id 44 :name "Rick"}]}

And you need to compute it once in one place and then pass it along
multiple layers of ui to this view. This is undesirable:

  • it will lead to unnecessary re-renderings of views that just pass data
    further when it changes
  • it complects reasoning about what actually a view needs: is it just a
    task? or a task with some precomputed attributes?

To mitigate this problem, cljfx introduces optional abstraction called
context, which is inspired by re-frame's subscriptions. Context is a
black-box wrapper around application state map, with an api
function fx/sub to look inside wrapped state. fx/sub usage has 2
flavors:

  1. Keys: anything except function, will return corresponding value from
    wrapped map.
  2. Subscription functions: any function that receives context as first
    argument. fx/sub-scribing to such functions will lead to a call to
    this function, and it in turn may subscribe to other keys and
    subscription functions.

Returned values from subscription functions are memoized in this context
(so it actually is a memoization context), and subsequent sub calls
will result in cache lookup. The best thing about context is that not
only does it support updating wrapped values via swap-context and
reset-context, it also reuses this memoization cache to minimize
re-calculation of subscription functions in successors of this context.
This is done via tracking of fx/sub calls inside subscription
functions, and checking if their dependencies changed. Example:

(def context-1
  (fx/create-context
    {:tasks [{:text "Buy milk" :done false}
             {:text "Buy socks" :done true}]}))

;; Simple subscription function that depends on :tasks key of wrapped map. Whenever value
;; of :tasks key "changes" (meaning whenever there will be created new context with
;; different value on :tasks key), subscribing to this function will lead to a call to
;; this function instead of cache lookup
(defn task-count [context]
  (count (fx/sub context :tasks)))

;; Using subscription functions:
(fx/sub context-1 task-count) ; => 2

;; Another subscription function depending on :tasks key of wrapped map
(defn remaining-task-count [context]
  (count (remove :done (fx/sub context :tasks))))

(fx/sub context-1 remaining-task-count) ; => 1

;; Indirect subscription function: it depends on 2 previously defined subscription
;; functions, which means that whenever value returned by `task-count` or
;; `remaining-task-count` changes, subscribing to this function will lead to a call
;; instead of cache lookup
(defn task-summary [context]
  (prn :task-summary)
  (format "Tasks: %d/%d"
          (fx/sub context remaining-task-count)
          (fx/sub context task-count)))

(fx/sub context-1 task-summary) ; (prints :task-summary) => "Tasks: 1/2"

;; Creating derived context that reuses cache from `context-1`
(def context-2
  (fx/swap-context context-1 assoc-in [:tasks 0 :text] "Buy bread"))

;; Validating that cache entry is reused. Even though we updated :tasks key, there is no
;; reason to call `task-summary` again, because it's dependencies, even though
;; recalculated, return the same values
(fx/sub context-2 task-summary) ; (does not print anything) => "Tasks: 1/2"

This tracking imposes a restriction on subscription functions: they
should not call fx/sub after they return (which is possible if they
return lazy sequence which may call fx/sub during element
calculation).

Using context in cljfx application requires 2 things:

  • passing context to all lifecycles in description graph, which is done
    by using fx/wrap-context-desc middleware
  • using special lifecycle (fx/fn->lifecycle-with-context) for function
    fx-types that uses this context

Minimal app example using contexts:

;; Define application state as context

(def *state
  (atom (fx/create-context {:title "Hello world"})))

;; Every description function receives context at `:fx/context` key

(defn root [{:keys [fx/context]}]
  {:fx/type :stage
   :showing true
   :scene {:fx/type :scene
           :root {:fx/type :h-box
                  :children [{:fx/type :label
                              :text (fx/sub context :title)}]}}})

(def renderer
  (fx/create-renderer
    :middleware (comp
                  ;; Pass context to every lifecycle as part of option map
                  fx/wrap-context-desc
                  (fx/wrap-map-desc (fn [_] {:fx/type root})))
    :opts {:fx.opt/type->lifecycle #(or (fx/keyword->lifecycle %)
                                        ;; For functions in `:fx/type` values, pass
                                        ;; context from option map to these functions
                                        (fx/fn->lifecycle-with-context %))}))

(fx/mount-renderer *state renderer)

Using contexts effectively makes every fx-type function a subscription
function, so no-lazy-fx-subs-in-returns restriction applies to them too.
On a plus side, it makes re-rendering very efficient: fx-type components
get re-rendered only when their subscription values change.

For a bigger example see
examples/e15_task_tracker.clj.

Another point of concern for context is cache. By default it will grow
forever, which at certain point might become problematic, and we may
want to trade some cpu cycles for recalculations to decrease memory
consumption. There is a perfect library for it:
core.cache. fx/create-context
supports cache factory (a function taking initial cache map and
returning cache) as a second argument. What kind of cache
to use is a question with no easy answer, you probably should try
different caches and see what is a better fit for your app.

Event handling on steroids

While using maps to describe events is a good step towards mostly pure
applications, there is still a room for improvement:

  • many event handlers dereference app state, which makes them coupled
    with an atom: mutable place
  • almost every event handler still mutates app state, which also makes
    them coupled
  • events are handled on JavaFX application thread, which may lead to
    responsiveness issues

Cljfx borrows solutions to all these problems from re-frame, providing
map event handler wrappers that allow having co-effects (pure inputs),
effects (pure outputs), and async handling. Lets walk through this
example event handler and see how we can make it pure:

(def *state
  (atom {:todos []}))

(defn handle [event]
  (let [state @*state
        {:keys [event/type text]} event]
    (case type
      ::add-todo (reset! *state (update state :todos conj {:text text :done false})))))

;; usage:
(handle {:event/type ::add-todo :text "Buy milk"})
  1. Co-effects: wrap-co-effects

    It would be nice to not have to deref state atom and instead receive
    it as an argument, and that is what co-effects are for. Co-effect is
    a term taken from re-frame, and it means current state as data, as
    presented to event handler. In cljfx you describe co-effects as a map
    from arbitrary key to function that produces some data that is then
    passed to handler:

    (defn handle [event]
      ;; receive state as part of an event
      (let [{:keys [event/type text state]} event]
        (case type
          ::add-todo (reset! *state (update state :todos conj {:text text :done false})))))
    
    (def actual-handler 
      (-> handle
          (fx/wrap-co-effects {:state #(deref *state)})))
    
    ;; usage:
    (actual-handler {:event/type ::add-todo :text "Buy milk"})
    
  2. Effects: wrap-effects

    Instead of performing side-effecting operations from handlers, we can
    return data that describes how to perform these side-effecting
    operations. fx/wrap-effects uses that data to perform side effects.
    You describe effects as a map from arbitrary keys to side-effecting
    function. Wrapped handler in turn should return a seqable of
    2-element vectors. First element is a key used to find side-effecting
    function, and second is an argument to it:

    (defn handle [event]
      (let [{:keys [event/type text state]} event]
        (case type
          ;; Now handlers not only receive just data, they also return just data
          ;; Returning map is a convenience option that can be used as a return
          ;; value, and sequences like [[:state ...] [:state ...]] are fine too 
          ::add-todo {:state (update state :todos conj {:text text :done false})})))
    
    (def actual-handler
      (-> handle
          (fx/wrap-co-effects {:state #(deref *state)})
          (fx/wrap-effects {:state (fn [state _] (reset! *state state))})))
    

    In addition to value provided by wrapped handler, side-effecting
    function receives a function they can call to dispatch new events.
    While it's useless for resetting state, it can be useful in
    other circumstances. One is you can create a :dispatch effect that
    dispatches another events, and another is you can describe
    asynchronous operations such as http requests as just data. Examples
    of both can be found at examples/e18_pure_event_handling.clj.
    This approach allows to specify side effects in a few places, and
    then have easily testable handlers:

    (handle {:event/type ::add-todo
             :text "Buy milk"
             :state {:todos []}})
    => {:state {:todos [{:text "Buy milk", :done false}]}}
    ;; data in, data out, no mocks necessary! 
    
  3. Async handling: wrap-async

    Finally, you can wrap your handler with fx/wrap-async to offload
    event handling to background thread:

    (def actual-handler
      (-> handle
          (fx/wrap-co-effects {:state #(deref *state)})
          (fx/wrap-effects {:state (fn [state _] (reset! *state state))})
          (fx/wrap-async)))
    

    Note that it uses agents underneath, so you will need to call
    clojure.core/shutdown-agents on exit. Another thing to keep in mind
    is that there are couple of cases where you want event handling to
    be synchronous:

    • when syncing typed text in input fields with app state by using
      :text and :on-text-changed props to avoid text reverts when
      typing too fast;
    • when dispatching events on startup that prepare some views to avoid
      showing empty screens.

    In these cases you can put :fx/sync true to event map: that will
    block call to event handler until this event is processed.

How does it actually work

There are 3 main building blocks of cljfx: components, lifecycles and
mutators. Each are represented by protocols, here they are:

(defprotocol Component
  :extend-via-metadata true
  (instance [this]))

(defprotocol Lifecycle
  :extend-via-metadata true
  (create [this desc opts])
  (advance [this component desc opts])
  (delete [this component opts]))

(defprotocol Mutator
  :extend-via-metadata true
  (assign! [this instance coerce value])
  (replace! [this instance coerce old-value new-value])
  (retract! [this instance coerce value]))

Component is an immutable value representing some object in some state
(that object may be mutable — usually it's a javafx object), that also
has a reference to said object instance.

Lifecycle is well, a lifecycle of a component. Component gets created
from a description once, advanced to new description zero or more times,
and then deleted. Cljfx is a composition of multiple different
lifecycles, each useful in their own place. opts is a map that
contains some data used by different lifecycles. 2 opt keys that are
used by default in cljfx are:

  • :fx.opt/type->lifecycle — used in dynamic lifecycle to select what
    lifecycle will be actually used for description based by value in
    :fx/type key.
  • :fx.opt/map-event-handler — used in event-handler lifecycle that
    checks if event handler is a map, and if it is, call function provided
    by this key when event happens. It should be noted, that such event
    handlers receive additional key in a map (:fx/event) that contains
    event object, which may be context dependent: for JavaFX change
    listeners it's a new value, for JavaFX event handlers it's an event,
    for runnables it's nil, etc.

Another notable lifecycle is cljfx.composite/lifecycle: it
manages mutable JavaFX objects: creates instance in create, advances
any changes to props (each individual prop may be seen as lifecycle +
mutator), and has some useful macros to simplify generating composite
lifecycles for concrete classes.

Finally, mutator is a part of prop in composite lifecycles that
performs actual mutation on instance when values change. It also
receives coerce function which is called on value before applying it.
Most common mutator is setter, but there are some other, for example,
property-change-listener, which uses addListener and
removeListener.

Extending cljfx

Cljfx might have some missing parts that you'll want to fill. Not
everything can be configured with lifecycle opts and renderer
middleware, and in that case you are encouraged to create and use
extension lifecycles. Fx-types in descriptions can be implementations of
Lifecycle protocol, and with this escape hatch you get a lot more
freedom. Since these lifecycles can introduce different meanings for
what descriptions mean in their context, they should stand out from
other keyword or function lifecycles, and convention is to have ext-
prefix in their names.

Included extension lifecycles

  1. fx/ext-instance-factory

    Using this extension lifecycle you can simply create a component
    using 0-argument factory function:

    (fx/instance
      (fx/create-component
        {:fx/type fx/ext-instance-factory
         :create #(Duration/valueOf "10ms")}))
    => #object[javafx.util.Duration 0x2f5eb358 "10.0 ms"]
    
  2. fx/ext-on-instance-lifecycle

    You can use this lifecycle to additionally setup/tear down instance
    of otherwise declaratively created value:

    (fx/instance
      (fx/create-component
        {:fx/type fx/ext-on-instance-lifecycle
         :on-created #(prn "created" %)
         :desc {:fx/type fx/ext-instance-factory
                :create #(Duration/valueOf "10ms")}}))
    ;; prints "created" #object[javafx.util.Duration 0x284cdce9 "10.0 ms"]
    => #object[javafx.util.Duration 0x284cdce9 "10.0 ms"]
    
  3. fx/ext-let-refs and fx/ext-get-ref

    You can create managed components outside of component tree using
    fx/ext-let-refs, and then use instances of them, possibly in
    multiple places, using fx/ext-get-ref:

    {:fx/type fx/ext-let-refs
     :refs {::button-a {:fx/type :button
                        :text "Press Alt+A to focus on me"}}
     :desc {:fx/type :v-box
            :children [{:fx/type :label
                        :text "Mnemonic _A"
                        :mnemonic-parsing true
                        :label-for {:fx/type fx/ext-get-ref
                                    :ref ::button-a}}
                       {:fx/type fx/ext-get-ref
                        :ref ::button-a}]}}
    

    One use case is for using references in props that expect nodes in a
    scene graph (such as label's :label-for), and another is having
    dialogs defined close to usage places, you can find an example of
    such dialog at examples/e22_button_with_confirmation_dialog.clj

  4. fx/ext-set-env and fx/ext-get-env

    You can put any values into component tree environment with fx/ext-set-env, and then
    retrieve values from this environment with fx/ext-get-env:

    {:fx/type fx/ext-set-env
     :env {::global-text-style {:-fx-text-fill :red}}
     :desc {:fx/type :v-box
            :children [{:fx/type fx/ext-get-env
                        :env {::global-text-style :style}
                        :desc {:fx/type :label 
                               ;; will receive :style prop that makes text red
                               :text "Hello world"}}]}}
    
  5. fx/ext-many

    Usually props that expect collections of elements already ask for a
    collection of descriptions, but there might be cases where you want to manage
    a coll even though you are asked for a single element. In this case you can
    use fx/ext-many to describe multiple of components, for example, to show
    multiple windows at once:

    (fx/on-fx-thread
      (fx/create-component
        {:fx/type fx/ext-many
         :desc [{:fx/type :stage
                 :showing true}
                {:fx/type :stage
                 :showing true}]}))
    

    See examples/e10_multiple_windows.clj
    and examples/e17_dialogs.clj

  6. fx/make-ext-with-props

    Using this function you can create extension lifecycles that handle whatever
    additional props you need. These props will be applied after props of
    original lifecycle. There are some predefined lifecycles providing extra
    props for controlling default selection models in TabPane, ListView,
    TableView, TreeView and TreeTableView, see examples/e27_selection_models.clj.

Examples of included extension lifecycles are available at
examples/e21_extension_lifecycles.clj.

Writing extension lifecycles

If that's not enough, you can write your own, but this requires more
thorough knowledge of cljfx: take a look at
cljfx.lifecycle namespace to see how other
lifecycles are implemented.

Wrapping other java-based JavaFX components

There is cljfx.composite/props macro to create a prop-map for
arbitrary Java class. Also there is a cljfx.composite/describe macro
that allows to construct a lifecycle from a class and a prop map, and
plenty of examples in cljfx.fx.* namespaces that can help you make
custom java components for JavaFX cljfx-friendly.

Combining it all together

Now that every piece is laid out, it's time to combine them into
application. What suits your needs is up to you, but if you plan to
build something non-trivial, you'll probably want to combine all of the
pieces, and easiest way to start is using create-app function. It
accepts app atom, event handler and function producing view description
and wires them all together:

(def app
  (fx/create-app *context
    :event-handler handle-event
    :desc-fn (fn [_]
               {:fx/type root-view})))

Using that as a starting point, you can build your application using
pure functions for everything: views, subscriptions, events.
create-app also allows some optional settings, such as :effects,
:co-effects and :async-agent-options for configuring event handling
and :renderer-middleware for configuring renderer. An example of such
application can be found at
examples/e20_markdown_editor.clj.

Gotchas

:fx/key should be put on descriptions in a list, not inside these descriptions

For example:

;; Don't do it, this won't work:

(defn item-view [{:keys [item]}]
  {:fx/type :label
   ;; Do not specify `:fx/key` here!
   :fx/key (:id item)
   :text (:title item)})

(defn item-list-view [items]
  {:fx/type :v-box
   :children (for [i items]
               {:fx/type item-view
                :item i})})

Lifecycle that manages lists of things (dynamics) can't see how it's
elements will unfold, so it needs to have :fx/key-s where it can see
them — in the element descriptions that it gets:

;; Do this to specify `:fx/key`-s:

(defn item-view [{:keys [item]}]
  {:fx/type :label
   :text (:title item)})

(defn item-list-view [items]
  {:fx/type :v-box
   :children (for [i items]
               {:fx/type item-view
                ;; Put `:fx/key` to description that is a part of a list
                :fx/key (:id i)
                :item i})})

Only mutable objects are described with :fx/type

Lifecycles describe how things change, and some things in JavaFX don't
change. For example, Insets class represents an immutable value, so
when describing padding you don't need a map with :fx/type key:

{:fx/type :region
 :padding {:top 10 :bottom 10 :left 10 :right 10}}

It doesn't have to be a map at all:

{:fx/type :region
 :padding 10}

How does it work? Instead of using lifecycle there is a coercion
mechanism that transforms values before assigning them to a model, most
of them are in cljfx.coerce namespace.

Coercion

Some notable coercion examples and approaches:

  • all enums and enum-like things can be expressed as kebab-cased
    keywords, for example :red for colors, :crosshair for cursors
  • you still can use actual instances of target classes, for example
    Cursor/CROSSHAIR for cursors
  • for classes with 1-arg constructors you can supply just that, for
    example url string for images
  • for classes with multi-arg constructors you can supply args as a map,
    for example map with :url and :background-loading for images
  • styles can be specified as maps, for example
    {:-fx-background-color :lightgray}
  • durations can be specified as vector like [10 :ms] or [2 :h]
  • key combinations can be vectors. There are 2 flavors of key
    combinations in JavaFX: KeyCodeCombination, created if last element of
    that vector is keyword, for example, [:ctrl :period], and
    KeyCharacterCombination, created if last element of that vector is
    string, for example [:ctrl "."]

Differences with JavaFX

There are some "synthetic" properties that provide needed functionality
usually used through some other API:

  • Canvas has a :draw prop that is a function that receives Canvas as
    an argument and should use it to draw on it (example)
  • MediaPlayer has :state prop that can be either :playing,
    :paused or :stopped, and will call play/pause/stop methods
    on media player when this prop is changed
  • :url prop of WebView will call load method on this view's web
    engine

No local mutable state

One thing that is easy to do in react/reagent, but actually complects
things, is local mutable state: every component can have it's own
mutable state that lives independently from overall app state. This
makes reasoning about state of the app harder: you need to take lots of
small pieces into account. Another problem is this state is unreliable,
because it is only here when a component is here. And if it gets
recreated, for example, after closing some panel it resides in and
reopening it back, this state will be lost. Sometimes we want this
behavior, sometimes we don't, and it's possible to choose whether this
state will be retained or not only if it's a part of a global app state.

No controlled props

In react, setting value prop on text input makes it controlled,
meaning it can't be changed unless there is also a change listener
updating this value on typing. This is much harder to do in JavaFX, so
there is no such thing. But you still can keep typed text in sync with
internal state by having both :text and :on-text-changed props (see
example in examples/e09_todo_app.clj)

More examples

There are various examples available in examples folder.
To try them out:

  1. Clone this repo and cd into it:
    git clone https://github.com/cljfx/cljfx.git
    cd cljfx 
    
  2. Ensure you have java 11 installed.
  3. Launch repl with :examples alias and require examples:
    clj -A:examples
    # Clojure 1.10
    # user=> (require 'e15-task-tracker)
    # nil ;; window appears
    

API stability, public and internal code

Newer versions of cljfx should never introduce breaking changes, so if
an update broke something, please file a bug report. Growth of cljfx
should happen only by accretion (providing more), relaxation (requiring
less) and fixation (bashing bugs).

This applies to public API of cljfx. cljfx.api namespace and all
behaviors that can be observed by using it are a public API. Other
namespaces have a docstring stating what is and is not a public API.

Current shapes of values implementing Lifecycle, Component and
Mutator protocols are internal and subject to change: treat them as
a protocol implementations only. Context is not a protocol, but it's
shape is internal too.

Keywords with fx namespace in component descriptions are reserved: new
ones may be introduced.

Getting help

Feel free to ask questions on Slack
or create an issue. Have a look at previously asked questions.

Food for thought

Internal list of ideas to explore:

  • missing observable maps: Scene's getMnemonics
  • :row-factory in tree-view/tree-table-view should be similar to cell
    factories
  • make exceptions more informative
  • are controlled props possible? (controls, also stage's :showing)
  • wrap-factory may use some memoizing and advancing
  • add tests for various lifecycles and re-calculations
  • update to same desc should be identical (component-vec)
  • expand on props and composite lifecycle. What's known about them:
    • ctor:
      • scene requires root, root can be replaced afterwards
      • xy-chart requires axis, they can't be replaced afterwards
    • prop in composite lifecycle may be a map or a function taking
      instance and returning prop!
    • changing media should re-create media player
  • big app with everything in it to check if/how it works (generative
    tests maybe?)
  • if animation is to be implemented, it probably should be done as in
    https://popmotion.io/
  • declarative timers? problem is to figure out start/loop semantics.
    Examples:
    • caret in custom text input may have timer that restarts on typing
    • flipbook animation player needs to restart timer on FPS settings
      change

主要指標

概覽
名稱與所有者cljfx/cljfx
主編程語言Clojure
編程語言Clojure (語言數: 4)
平台Linux, Mac, Windows
許可證MIT License
所有者活动
創建於2018-12-22 22:02:32
推送於2025-04-10 16:08:03
最后一次提交2025-04-10 18:07:59
發布數74
最新版本名稱1.9.5 (發布於 )
第一版名稱0.1.0 (發布於 )
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