动态加载JWplayer(Loading JWplayer dynamically)

 首先，有一个回归影响了这里的代码。 这个问题现在已经解决了。 Threepenny 0.6.0.3有一个临时修复，最终版本将包含在发布之后。 
 
 
 您提供的pastebin中的代码几乎是正确的。 唯一需要的改变是你不需要在按钮点击回调中使用接收sink - 在你的情况下，接收sink应该在行为和文本区域的内容之间建立永久连接，行为值响应于按钮单击事件。 
 
 为了完整起见，这是一个完整的解决方案： 
 
{-# LANGUAGE RecursiveDo #-}
module Main where

import Control.Applicative
import Control.Monad
import Data.Maybe

import qualified Graphics.UI.Threepenny as UI
import Graphics.UI.Threepenny.Core

main :: IO ()
main = startGUI defaultConfig setup

setup :: Window -> UI ()
setup w = void $ mdo
    return w # set UI.title "Simple example"

    listBox <- UI.listBox
        (pure ["First", "Second"]) bSelected (pure $ UI.string)
    button  <- UI.button # set UI.text "Button"
    display <- UI.textarea

    element listBox # set (attr "size") "10"

    getBody w #+ [element listBox, element button, element display]

    bSelected <- stepper Nothing $ rumors (UI.userSelection listBox)
    let eClick = UI.click button
        eValue = fromMaybe "No selection" <$> bSelected <@ eClick
    bValue    <- stepper "Initial value" eValue

    element display # sink UI.text bValue
 
 要带走的两件关键事项是： 
 
 
 
 listBox的Behavior (Maybe a)参数不仅设置初始选定值，而是确定应用程序整个生命周期中值的演变。 在这个例子中， facts $ UI.userSelection listBox只是bSelected ，可以通过Widgets模块的源代码验证。 
 
 
 在事件发生时采样行为的典型方法是通过(<@) （或<@>如果事件包含您希望使用的数据）。 
 

First of all, there was a regression which affected the code here. That issue is now solved. Threepenny 0.6.0.3 has a temporary fix, and the definitive one will be included in the release after that.
 
 
The code in the pastebin you provided is almost correct. The only needed change is that you don't need to use sink within the button click callback - in your case, sink should establish a permanent connection between a behavior and the content of the text area, with the behavior value changing in response to the button click events.
 
For the sake of completeness, here is a full solution:
 
{-# LANGUAGE RecursiveDo #-}
module Main where

import Control.Applicative
import Control.Monad
import Data.Maybe

import qualified Graphics.UI.Threepenny as UI
import Graphics.UI.Threepenny.Core

main :: IO ()
main = startGUI defaultConfig setup

setup :: Window -> UI ()
setup w = void $ mdo
    return w # set UI.title "Simple example"

    listBox <- UI.listBox
        (pure ["First", "Second"]) bSelected (pure $ UI.string)
    button  <- UI.button # set UI.text "Button"
    display <- UI.textarea

    element listBox # set (attr "size") "10"

    getBody w #+ [element listBox, element button, element display]

    bSelected <- stepper Nothing $ rumors (UI.userSelection listBox)
    let eClick = UI.click button
        eValue = fromMaybe "No selection" <$> bSelected <@ eClick
    bValue    <- stepper "Initial value" eValue

    element display # sink UI.text bValue
 
The two key things to take away are:
 
 
 
The Behavior (Maybe a) argument to listBox does not set just the initial selected value, but determines the evolution of the value throughout the lifetime of the application. In this example, facts $ UI.userSelection listBox is just bSelected, as can be verified through the source code of the Widgets module.
 
 
The typical way to sample a behavior on event occurrences is through (<@) (or <@> if the event carries data you wish to make use of).